Stock Option Agreement - Cornerstone Properties Inc., Equity Office Properties Trust and Deutsche Bank AG


                             STOCK OPTION AGREEMENT

                  THIS STOCK OPTION AGREEMENT (this 'Agreement') is entered into
as of February 11, 2000, by and among CORNERSTONE PROPERTIES INC., a Nevada
corporation ('Cornerstone'), EQUITY OFFICE PROPERTIES TRUST, a Maryland real
estate investment trust ('EOP'), DEUTSCHE BANK AG der Deutschen Bank, a stock
corporation organized under German law ('Deutsche Bank'), and DEUTSCHER HEROLD
LEBENSVERSICHERUNGS-AG, a stock corporation organized under German law and an
indirect subsidiary of Deutsche Bank ('Deutscher Herold').

                  In consideration of the mutual covenants and agreements
contained herein and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, and intending to be legally bound
hereby, the parties hereto hereby agree as follows:


                                    ARTICLE I
                                THE STOCK OPTION

                  1.1 GRANT OF STOCK OPTION. Each of Deutsche Bank and Deutscher
Herold hereby grant to each of Cornerstone and EOP (each, a 'Purchaser') an
irrevocable option (the 'Stock Option') to purchase, subject to the terms
hereof, the number of fully paid and non-assessable shares of 7.0% Cumulative
Convertible Preferred Stock, with no par value, of Cornerstone ('Cornerstone
Preferred Stock') set forth on SCHEDULE A attached hereto opposite its name,
subject to adjustment pursuant to Section 5 hereof (such shares of Cornerstone
Preferred Stock held by Deutsche Bank and Deutscher Herold are referred to
collectively as the 'Option Shares'), at a purchase price of $18.00 in cash per
share of Cornerstone Preferred Stock or, if the Merger Agreement (as defined
herein) is amended to increase the price per share of a share of Cornerstone
common stock, no par value, in excess of $18.00 per share, then at a purchase
price in cash equal to such greater price per share of Cornerstone common stock,
no par value, as is so specified in the Merger Agreement, as so amended, in each
case together with the dividends accrued and unpaid to the date of the Option
Closing (the 'Purchase Price'), and in the manner set forth in Sections 1.2, 1.3
and 1.4 hereof.

                  1.2  EXERCISE OF THE STOCK OPTION.

                           (a) The Stock Option may be exercised by Cornerstone
or EOP, in whole but not in part, at any time or from time to time prior to
termination of the Stock Option in accordance with this Section 1.2 and Section
9.8 hereof.

                           (b) If at any time Cornerstone desires to exercise
the Stock Option, Cornerstone shall (1) deliver to each of Deutsche Bank and
Deutscher Herold a written notice (a 'Cornerstone Exercise Notice,' with the
date of the



Cornerstone Exercise Notice being hereinafter called the 'Cornerstone Notice
Date') notifying each of Deutsche Bank and Deutscher Herold of its exercise of
the Stock Option and (2) on the Cornerstone Notice Date, deliver to EOP a copy
of the Cornerstone Exercise Notice. The closing of such exercise by Cornerstone
of the Stock Option (the 'Cornerstone Option Closing') shall occur on the third
business day immediately following the Cornerstone Notice Date at a time and at
a place in New York, New York designated by Cornerstone in the Cornerstone
Exercise Notice. 'Business Day' means a business day in Frankfurt, Bonn and New
York.

                           (c) Subject to Section 1.2(d) hereof, if at any time
EOP desires to exercise the Stock Option, EOP shall (1) deliver to each of
Deutsche Bank and Deutscher Herold a written notice (an 'EOP Exercise Notice,'
with the date of the EOP Exercise Notice being hereinafter called the 'EOP
Notice Date') notifying each of Deutsche Bank and Deutscher Herold of its
exercise of the Stock Option and (2) on the EOP Notice Date, deliver to
Cornerstone a copy of the EOP Exercise Notice; PROVIDED, HOWEVER, that EOP shall
not be entitled to exercise the Stock Option or to deliver an EOP Exercise
Notice if Cornerstone has delivered a Cornerstone Exercise Notice in accordance
with the terms of this Agreement and the date for the Cornerstone Option Closing
corresponding to such Cornerstone Option Closing, as set forth in Section 1.2(b)
hereof, has not passed. Subject to Section 1.2(d) hereof, the closing of such
exercise by EOP of the Stock Option (the 'EOP Option Closing') shall occur on
the ninth business day immediately following the EOP Notice Date at a time and
at a place in New York, New York designated by EOP in the EOP Exercise Notice.

                           (d) Upon receipt of an EOP Exercise Notice,
Cornerstone shall have the right, exercisable at any time prior to 5:00 p.m.,
New York time, on the second business day after the EOP Notice Date, to (1)
deliver to each of Deutsche Bank and Deutscher Herold a Cornerstone Exercise
Notice notifying each of Deutsche Bank and Deutscher Herold of its exercise of
the Stock Option and (2) on the Cornerstone Notice Date, deliver to EOP a copy
of the Cornerstone Exercise Notice. If Cornerstone so exercises the Stock
Option, the Cornerstone Option Closing shall occur on the third business day
immediately following the Cornerstone Notice Date at a time and at a place in
New York, New York designated by Cornerstone in the Cornerstone Exercise Notice.
Upon Cornerstone's purchase of the Option Shares pursuant thereto, the EOP
Exercise Notice delivered pursuant to Section 1.2(d) shall be deemed of no force
or effect.

                           (e) Upon receipt of a Cornerstone Exercise Notice,
each of Deutsche Bank and Deutscher Herold shall be obligated, provided that the
conditions specified in Section 1.3 hereto shall be satisfied, to deliver to
Cornerstone a certificate or certificates evidencing the Option Shares held by
it, in accordance with the terms of this Agreement, on the third business day
immediately following the Cornerstone Notice Date.

                                      -2-


                           (f) On the date set for closing of any purchase of
Option Shares hereunder, each of Deutsche Bank and Deutscher Herold shall,
subject to satisfaction of the conditions specified in Section 1.3 hereof and
receipt of the Purchase Price therefor, deliver to Purchaser (i) a certificate
or certificates representing the Option Shares held by it, properly endorsed or
otherwise in proper form for transfer, and (ii) an irrevocable proxy in form
reasonably acceptable to Purchaser authorizing Purchaser or its designee to vote
such Option Shares on all matters submitted to a vote of the holders of
Cornerstone Preferred Stock.

                  1.3 CONDITIONS TO DELIVERY OF THE OPTION SHARES. The right of
each of Cornerstone or EOP to exercise the Stock Option and the obligation of
each of Deutsche Bank and Deutscher Herold to deliver the Option Shares held by
it upon the exercise of the Stock Option are subject to the following
conditions:

                           (a) Such delivery would not violate in any material
respect, or otherwise cause a material violation of, any material Law (as
defined herein), including, without limitation, under the Hart-Scott-Rodino
Antitrust Improvements Act of 1976, as amended ('Hart-Scott-Rodino'), applicable
to such exercise of Stock Option and the delivery of the Option Shares; and

                           (b) There shall be no preliminary or permanent
injunction or other order by any court of competent jurisdiction preventing or
prohibiting such exercise of the Stock Option or the delivery of Option Shares
in respect of such exercise.

                  1.4 CLOSING. At the Option Closing, Cornerstone or EOP, as
applicable, shall pay to each of Deutsche Bank and Deutscher Herold, upon
receipt of the certificate or certificates and proxy pursuant to Section 1.2(f),
the aggregate Purchase Price for Option Shares to be purchased by Cornerstone or
EOP, as applicable (net of any taxes required to be held pursuant to Section
1445 of the Internal Revenue Code of 1986, as amended), by wire transfer of
immediately available funds to an account(s) designated by each of Deutsche Bank
and Deutscher Herold at least two business days prior to the Option Closing.

                  1.5 ADJUSTMENTS UPON SHARE ISSUANCES, CHANGES IN
CAPITALIZATION, ETC. In the event of any change in the Cornerstone Preferred
Stock or in the number of outstanding shares of Cornerstone Preferred Stock by
reason of a stock dividend, split-up, recapitalization, combination, exchange of
shares or similar transaction or any other change in the corporate or capital
structure of Cornerstone (including, without limitation, the declaration or
payment of an extraordinary dividend in the form of cash, securities or other
property), the type and number of shares or securities to be delivered by
Deutsche Bank and Deutscher Herold upon exercise of the Stock Option shall be
adjusted appropriately.

                                      -3-


                                   ARTICLE II
               REPRESENTATIONS AND WARRANTIES OF DEUTSCHE BANK AND
                                DEUTSCHER HEROLD

                  Each of Deutsche Bank and Deutscher Herold hereby represents
and warrants to each of Cornerstone and EOP as follows:

                  2.1 AUTHORITY RELATIVE TO THIS AGREEMENT. It has all requisite
corporate power and authority to execute and deliver this Agreement, to perform
its obligations hereunder and to consummate the transactions contemplated hereby
to be consummated by it. The execution and delivery of this Agreement by it and
the consummation by it of the transactions contemplated hereby have been duly
authorized by all necessary corporate action, and no other corporate proceedings
on the part of it are necessary to authorize the execution and delivery of this
Agreement or to consummate the transactions contemplated hereby. This Agreement
has been duly executed and delivered by it and constitutes the legal, valid and
binding obligations of it, enforceable against it in accordance with its terms,
subject to applicable bankruptcy, insolvency, moratorium or other similar Laws
relating to creditors' rights and general principles of equity.

                  2.2 NO LIENS. The Option Shares shall be delivered free and
clear of all security interests, liens, claims, pledges, options, rights of
first refusal, agreements, limitations on voting rights, charges and other
encumbrances of any nature whatsoever (other than this Agreement).

                  2.3 NO VIOLATION. The execution and delivery of this Agreement
by it do not, the performance of its obligations hereunder by it will not, the
consummation by it of the transactions contemplated to be performed by it
hereunder will not and the exercise by Cornerstone or EOP of the Stock Option
hereunder will not, (i) violate or conflict with any provision of any judgment,
order, decree, statute, law, ordinance, rule or regulation (collectively,
'Laws') in effect on the date of this Agreement and applicable to it (it being
understood that neither Deutsche Bank nor Deutscher Herold makes any
representation or warranty with respect to Hart-Scott-Rodino); (ii) require it
to obtain any consent, waiver, approval, license or authorization or permit of,
or make any filing with, or notification to, any governmental entities, based on
laws, rules, regulations and other requirements of governmental entities in
effect as of the date of this Agreement (it being understood that neither
Deutsche Bank nor Deutscher Herold makes any representation or warranty with
respect to Hart-Scott-Rodino); (iii) require the consent, waiver, approval,
license or authorization of any person (other than a governmental entity and
other than the property trustee (Deckungsstocktreuhander) of Deutscher Herold);
(iv) violate, conflict with or result in a breach of any obligation under, or
constitute a default (or an event which with notice or the lapse of time or both
would become a default) under, or give to others any rights of, or result in
any, termination, amendment, acceleration or cancellation of, or loss of any
benefit or

                                      -4-


creation of a right of first refusal, or require any payment under, any
provision of any indenture, mortgage, note, bond, lien, lease, license,
agreement, contract, order, judgment, ordinance, permit or other instrument or
obligation to which it is a party or by which it is bound or subject to; or (v)
conflict with or violate the articles or certificate of incorporation or bylaws,
or the equivalent organizational documents, in each case as amended or restated,
of it.


                                   ARTICLE III
                  REPRESENTATIONS AND WARRANTIES OF CORNERSTONE

                  Cornerstone hereby represents and warrants to each of Deutsche
Bank and Deutscher Herold that it has all requisite corporate power and
authority to execute and deliver this Agreement, to perform its obligations
hereunder and to consummate the transactions contemplated hereby to be
consummated by Cornerstone. The execution and delivery of this Agreement by
Cornerstone have been duly authorized by the Board of Directors of Cornerstone.
This Agreement has been duly executed and delivered by Cornerstone and
constitutes the legal, valid and binding obligations of it, enforceable against
it in accordance with its terms, subject to applicable bankruptcy, insolvency,
moratorium or other similar laws relating to creditors' rights and general
principles of equity.


                                   ARTICLE IV
                            COVENANTS OF CORNERSTONE

                  Cornerstone hereby covenants and agrees that it shall acquire
Option Shares and/or other securities acquired upon its exercise of the Stock
Option for investment purposes only and not with a view to any distribution
thereof in violation of the Securities Act of 1933, as amended (the 'Securities
Act'), and immediately shall cancel the Option Shares upon their purchase by
Cornerstone hereunder.


                                    ARTICLE V
                      REPRESENTATIONS AND WARRANTIES OF EOP

                  EOP hereby represents and warrants to each of Deutsche Bank
and Deutscher Herold that it has all requisite trust power and authority to
execute and deliver this Agreement, to perform its obligations hereunder and to
consummate the transactions contemplated hereby to be consummated by EOP. The
execution and delivery of this Agreement by EOP have been duly authorized by the
Board of Trustees of EOP. This Agreement has been duly executed and delivered by
EOP and constitutes the legal, valid and binding obligations of it, enforceable
against it in accordance with its terms, subject to applicable bankruptcy,
insolvency,

                                      -5-


moratorium or other similar laws relating to creditors' rights and general
principles of equity.


                                   ARTICLE VI
                                COVENANTS OF EOP

                  EOP hereby covenants and agrees that it shall acquire Option
Shares and/or other securities acquired upon its exercise of the Stock Option
for investment purposes only and not with a view to any distribution thereof in
violation of the Securities Act, and shall not sell any such securities
purchased pursuant to this Agreement except in compliance with the Securities
Act.


                                   ARTICLE VII
                 COVENANTS OF DEUTSCHE BANK AND DEUTSCHER HEROLD

                  Each of Deutsche Bank and Deutscher Herold shall not, directly
or indirectly, and shall cause each of its affiliates not to, directly or
indirectly, (a) sell, transfer, pledge, encumber, assign or otherwise dispose
of, or enter into any contract, option or other agreement or understanding with
respect to the sale, transfer, pledge, encumbrance, assignment or other
disposition of, Option Shares, (b) grant any proxies for any Option Shares, (c)
deposit any Option Shares into a voting trust or enter into a voting agreement
with respect to any Option Shares, or tender any Option Shares in a transaction,
or (d) take any action which is intended to have the effect of preventing or
disabling Deutsche Bank or Deutscher Herold from performing its obligations
under this Agreement; PROVIDED, HOWEVER, that nothing herein shall prevent the
sale, transfer, pledge or assignment of any of such Option Shares, provided that
the purchaser, transferee, pledgee or assignee thereof agrees in writing to be
bound by the terms of this Agreement. To enable either of the Purchasers to
enforce the transfer restrictions contained in this Article VII, each of
Deutsche Bank and Deutscher Herold hereby consents to the placing of
stop-transfer orders with the transfer agent of the Cornerstone Preferred Stock.

                                      -6-


                                  ARTICLE VIII
                          WAIVER OF DISSENTERS' RIGHTS

                  Each of Deutsche Bank and Deutscher Herold hereby irrevocably
and forever waives any and all rights it may have under Chapter 92A of the
General Corporation Law of Nevada with respect to any of the transactions
contemplated by that certain Merger Agreement, dated as of February 11, 2000, by
and among EOP, EOP Partnership, Cornerstone and Cornerstone Partnership (the
'Merger Agreement'). Notwithstanding the foregoing, the foregoing waiver shall
be of no force or effect after December 31, 2000.


                                   ARTICLE IX
                                  MISCELLANEOUS

                  9.1 EXPENSES. Except as expressly provided herein to the
contrary, each party hereto shall pay all of its expenses in connection with the
transactions contemplated by this Agreement, including, without limitation, the
fees and expenses of its counsel and other advisors.

                  9.2 NOTICES. All notices and other communications given or
made pursuant hereto shall be in writing and shall be given (and shall be deemed
to have been duly given upon receipt) by delivery in person, by telecopy or
facsimile, by registered or certified mail (postage prepaid, return receipt
requested), or by a nationally recognized courier service to the parties at the
following addresses (or at such other address for a party as shall be specified
by like changes of address) or, if sent by telecopy or facsimile, to the parties
at the telecopier numbers specified below:


                                          
                  If to Cornerstone:         Cornerstone Properties Inc.
                                             126 East 56th Street
                                             New York, NY  10022
                                             Attention: Lee Van Boven, Esq.
                                             Telecopier: 650-345-8264

                  With a copy                King & Spalding
                  (which shall not           191 Peachtree Street
                  constitute notice) to:     Atlanta, GA 30303-1763
                                             Attention: William B. Fryer, Esq.
                                             Telecopier: 404-572-5100


                                      -7-



                                          
                  If to EOP:                 Equity Office Properties Trust
                                             Two North Riverside Plaza
                                             Chicago, IL 60606
                                             Attention: Stanley M. Stevens, Esq.
                                             Telecopier: 312-559-5021

                  With copies                Hogan & Hartson L.L.P.
                  (which shall not           555 13th Street, N.W.
                  constitute notice) to:     Washington, D.C. 20004
                                             Attention: J. Warren Gorrell, Jr., Esq.
                                                        George P. Barsness, Esq.
                                             Telecopier: 202-637-5910


                  If to Deutsche Bank:       Deutsche Bank AG
                                             Group Investments
                                             Taunusanlage 12
                                             60325 Frankfurt am Main
                                             GERMANY
                                             Attention: Lutz Robra
                                             Telecopier: 49 69 910-43583

                  With a copy                White & Case LLP
                  (which shall not           1155 Avenue of the Americas
                  constitute notice) to:     New York, NY 10036
                                             Attention: Duane D. Wall, Esq.
                                             Telecopier: (212) 819-8200


                  If to Deutscher Herold:    Deutscher Herold Lebensversicherungs-AG
                                                 der Deutschen Bank
                                             Poppelsdorfer Allee 25-33
                                             53115 Bonn
                                             GERMANY
                                             Attention: Mr. J. Klahn
                                             Telecopier: 49 228 268 3838

                  With copies                 White & Case LLP
                  (which shall not            1155 Avenue of the Americas
                  constitute notice) to:      New York, NY 10036
                                              Attention: Duane D. Wall, Esq.
                                              Telecopier: (212) 819-8200


                                      -8-


                  9.3 ENTIRE AGREEMENT. This Agreement constitutes the entire
agreement between the parties and supersedes all prior agreements and
understandings, both written and oral, between the parties, or any of them, with
respect to the subject matter hereof.

                  9.4 ASSIGNMENT. Neither this Agreement nor any rights or
obligations hereunder shall be assigned by operation of law or otherwise,
without the prior written consent of the other party hereto; PROVIDED, HOWEVER,
that EOP may assign this Agreement or any of its rights or obligations hereunder
to EOP Operating Limited Partnership, a Delaware limited partnership ('EOP
Partnership'), without the consent of any other party hereto; PROVIDED, FURTHER,
HOWEVER, that Cornerstone may assign this Agreement or any of its rights or
obligations hereunder to Cornerstone Properties Limited Partnership, a Delaware
limited partnership ('Cornerstone Partnership'), without the consent of any
other party hereto (PROVIDED, HOWEVER, that Cornerstone Partnership agrees to
cause Cornerstone to cancel the Option Shares immediately upon any purchase by
Cornerstone Partnership hereunder).

                  9.5 GOVERNING LAW. This Agreement, and all matters relating
hereto, shall be governed by, and construed in accordance with the laws of the
State of Maryland, regardless of the laws that might govern under applicable
principles of conflict of law theory.

                  9.6 CONSENT TO JURISDICTION; WAIVER OF JURY TRIAL. Each of
Deutsche Bank and Deutscher Herold hereby submits and consents to non-exclusive
personal jurisdiction in any action, suit or proceeding arising out of this
Agreement or the transactions contemplated hereby (and for no other purposes) in
a federal court located in the State of Maryland or in a Maryland state court.
Any process, summons, notice or document delivered by mail to the address set
forth in Section 9.2 shall be effective service of process for any action, suit
or proceeding in any Maryland state court or any federal court located in the
State of Maryland with respect to any matters to which Deutsche Bank or
Deutscher Herold has submitted to jurisdiction in this Section 9.6. Each of
Deutsche Bank and Deutscher Herold irrevocably and unconditionally waives any
objection to the laying of venue of any action, suit or proceeding arising out
of this Agreement or the transactions contemplated hereby in any Maryland state
court or any federal court located in the State of Maryland, and hereby
irrevocably and unconditionally waives and agrees not to plead or claim in any
such court that any such action, suit or proceeding brought in any such court
has been brought in an inconvenient forum. EACH OF DEUTSCHE BANK AND DEUTSCHER
HEROLD IRREVOCABLY WAIVES TRIAL BY JURY IN ANY ACTION, SUIT OR PROCEEDING WITH
RESPECT TO THIS AGREEMENT.

                  9.7 INJUNCTIVE RELIEF. The parties agree that in the event of
a breach of any provision of this Agreement irreparable damage would occur, the
aggrieved

                                      -9-


party would be without an adequate remedy at law and damages would be difficult
to determine. The parties therefore agree that in the event of a breach of any
provision of this Agreement, the aggrieved party may elect to institute and
prosecute proceedings in any court of competent jurisdiction to enforce specific
performance or to enjoin the continuing breach of such provision. By seeking or
obtaining such relief, the aggrieved party shall not be precluded from seeking
or obtaining any other relief to which it may be entitled at law or in equity.

                  9.8 TERMINATION. The Stock Option shall terminate upon the
earlier of: (i) the consummation of the Cornerstone Option Closing or the EOP
Option Closing hereunder; (ii) the date which is the tenth day after the
termination of the Merger Agreement; or (iii) December 31, 2000.

                  9.9 COUNTERPARTS. This Agreement may be executed in any number
of counterparts, each of which shall be deemed to be an original and all of
which together shall constitute one and the same document.

                  9.10 SEVERABILITY. Any term or provision of this Agreement
which is invalid or unenforceable in any jurisdiction shall, as to such
jurisdiction, be ineffective to the extent of such invalidity or
unenforceability without rendering invalid or unenforceable the remaining terms
and provisions of this Agreement or affecting the validity or enforceability of
any of the terms or provisions of this Agreement in any other jurisdiction. If
any provision of this Agreement is so broad as to be unenforceable, such
provision shall be interpreted to be only so broad as to make it enforceable.

                  9.11 FURTHER ASSURANCES. Each party hereto shall execute and
deliver all such further documents and take all such further action as may be
necessary in order to consummate the transactions contemplated by this
Agreement.

                  9.12 THIRD PARTY BENEFICIARIES. Nothing in this Agreement,
expressed or implied, shall be construed to give any person other than the
parties hereto and their successors and permitted assigns any legal or equitable
right, remedy or claim under or by reason of this Agreement or any provision
contained herein.

                  9.13 AMENDMENT AND MODIFICATION. This Agreement may be
amended, modified and supplemented only by a written document executed by
Cornerstone, EOP, Deutsche Bank and Deutscher Herold.

                  9.14 TREATMENT OF CORNERSTONE PREFERRED STOCK IN THE MERGER.
Each share of Cornerstone Preferred Stock shall be converted in the Merger into
the right to receive $18.00, together with accrued and unpaid dividends to the
Effective Time of the Merger, in cash, as described in Section 1.10(b)(iii) of
the Merger Agreement.

                  9.15 PUT RIGHT. In the event that the Stock Option is not
exercised within two business days after the Effective Time of the Merger, each
of Deutsche

                                      -10-


Bank and Deutscher Herold shall have the right to require EOP to purchase the
Option Shares in the same manner and with the same effect as if EOP shall have
given an EOP Exercise Notice, whereupon EOP shall be required to purchase such
Option Shares in accordance with this Agreement.

                                      -11-



                  IN WITNESS WHEREOF, the parties have caused this Agreement to
be executed as of the date first written above by their respective officers
thereunto duly authorized.


                         CORNERSTONE PROPERTIES INC.

                         By:   /s/ John S. Moody
                         ---------------------------
                         Name:  John S. Moody
                         Title: President and Chief
                                Executive Officer


                         EQUITY OFFICE PROPERTIES TRUST

                         By:   /s/ Stanley M. Stevens
                         ----------------------------
                         Name:  Stanley M. Stevens
                         Title: Executive Vice President
                                and Chief Legal Counsel



                         DEUTSCHE BANK AG

                         By:   /s/ Lutz Robra             /s/ Gerald F. Bender
                         ---------------------------      ----------------------
                         Name:  Lutz Robra                Gerald F. Bender
                         Title: Director                  Senior Associate 
                                                            Director



                         DEUTSCHER HEROLD
                         LEBENSVERSICHERUNGS-AG

                         By:   /s/ K.R. Vias              /s/ J. Klahn
                         ---------------------------      ---------------------
                         Name:  K.R. Vias                 J. Klahn
                         Title: Director                  Director
 
                                      -12-


                                   SCHEDULE A

                           Cornerstone Properties Inc.
                    7% Cumulative Convertible Preferred Stock


Deutsche Bank AG                                         2,249,053 shares

Deutscher Herold Lebensversicherungs-AG                    781,250 shares




 TYPE:  EX-10.2
 SEQUENCE:  4
 DESCRIPTION:  EXHIBIT 10.2




                                                                    Exhibit 10.2


                                VOTING AGREEMENT

                                     (PGGM)


                  THIS VOTING AGREEMENT (this 'AGREEMENT') is entered into as of
February 11, 2000 by and among Equity Office Properties Trust, a Maryland real
estate investment trust ('EOP'), EOP Operating Limited Partnership, a Delaware
limited partnership ('EOP PARTNERSHIP'), WCP Services, Inc., a Delaware
corporation ('WCP'), and Stichting Pensioenfonds voor de Gezondheid, Geestelijke
en Maatschappelijke Belangen, a stichting formed according to the laws of the
Kingdom of The Netherlands ('PGGM').

                  WHEREAS, EOP, EOP Partnership, Cornerstone Properties, Inc., a
Nevada corporation ('Cornerstone'), Cornerstone Properties Limited Partnership,
a Delaware limited partnership ('CORNERSTONE PARTNERSHIP'), will enter into an
Agreement and Plan of Merger dated as of the date hereof (the 'MERGER
Agreement'), pursuant to which (i) Cornerstone Partnership will be merged with
and into EOP Partnership (the 'PARTNERSHIP MERGER'), with EOP Partnership as the
survivor of the Partnership Merger, and (ii) Cornerstone will be merged with and
into EOP (the 'MERGER'), with EOP as the survivor of the Merger (all capitalized
terms used but not defined herein shall have the meanings set forth in the
Merger Agreement);

                  WHEREAS, PGGM is the beneficial and record owner of 45,779,703
issued and outstanding shares of common stock, with no par value per share, of
Cornerstone (such shares, together with any shares acquired hereafter, the
'CORNERSTONE COMMON SHARES') as more particularly described on SCHEDULE 1;

                  WHEREAS, in accordance with the Recitals in the Merger
Agreement, PGGM desires to execute and deliver this Agreement solely in its
capacity as a holder of Cornerstone Common Shares; and

                  WHEREAS, to induce PGGM to enter into this Agreement, EOP, EOP
Partnership and WCP desire to make certain undertakings and agreements as set
forth herein.

                  NOW, THEREFORE, in consideration of the foregoing and for
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the parties hereto agree as follows:

SECTION 1.        DISPOSITION OF CORNERSTONE COMMON SHARES

                  During the period from the date hereof through the earlier of
(i) the date on which the Merger is consummated or (ii) 30 days after the date
on which



the Merger Agreement is terminated according to its terms (such period
hereinafter referred to as the 'TERM'), PGGM shall not, directly or indirectly,
(a) sell, transfer, pledge, encumber, assign or otherwise dispose of, or enter
into any contract, option or other agreement or understanding with respect to
the sale, transfer, pledge, encumbrance, assignment or other disposition of, any
Cornerstone Common Shares, (b) grant any proxies for any Cornerstone Common
Shares with respect to any matters described in Section 2(a) hereof (other than
a proxy directing the holder thereof to vote the Cornerstone Common Shares in a
manner required by Section 2(a) hereof), (c) deposit any Cornerstone Common
Shares into a voting trust or enter into a voting agreement with respect to any
Cornerstone Common Shares with respect to any matters described in Section 2(a)
hereof, or tender any Cornerstone Common Shares in a transaction other than a
transaction contemplated by the Merger Agreement, or (d) take any action which
is intended to have the effect of preventing or disabling PGGM from performing
its obligations under this Agreement; PROVIDED, HOWEVER, that nothing herein
shall prevent the sale, transfer, pledge, encumbrance, assignment or other
disposition of any of such Cornerstone Common Shares, provided that the
purchaser, transferee, pledgee or assignee thereof agrees in writing to be bound
by the terms of this Agreement.

SECTION 2.        VOTING

                  (a) During the Term, PGGM shall cast or cause to be cast all
votes attributable to the Cornerstone Common Shares, at any annual or special
meeting of shareholders of Cornerstone, including any adjournments or
postponements thereof, or in connection with any written consent or other vote
of Cornerstone shareholders, (i) in favor of adoption of the Merger Agreement
and approval of the Merger and the other transactions contemplated by the Merger
Agreement (including any amendments or modifications of the terms of the Merger
Agreement approved by the board of directors of Cornerstone that would not
materially adversely affect PGGM in its capacity as beneficial owner of
Cornerstone Common Stock), and (ii) against approval or adoption of any action
or agreement (other than the Merger Agreement or the transactions contemplated
thereby) made or taken in opposition to or in competition with the Merger or the
Partnership Merger.

                  (b) PGGM will retain the right to vote its Cornerstone Common
Shares, in its sole discretion, on all matters other than those described in
paragraph (a) of this Section 2, and PGGM may grant proxies and enter into
voting agreements or voting trusts for its Cornerstone Common Shares in respect
of such other matters.

SECTION 3.        NON-SOLICITATION

                  During the Term, PGGM (a) shall not, and shall not permit any
of its officers, directors, employees, Affiliates, agents, investment bankers,
financial advisors, attorneys, accountants, brokers, finders or other
representatives retained

                                      -2-


by it to, (i) invite, initiate, solicit or encourage, directly or indirectly,
any inquiries, proposals, discussions or negotiations or the making or
implementation of any Acquisition Proposal, or (ii) engage in any discussions or
negotiations with or provide any confidential or non-public information or data
to, any person relating to an Acquisition Proposal, or otherwise facilitate any
effort or attempt to make or implement an Acquisition Proposal; and (b) shall
notify EOP immediately if it receives any such inquiries or proposals, or any
requests for such information, or if any such negotiations or discussions are
sought to be initiated or continued with PGGM.

SECTION 4.        TAX MATTERS

                  (a) So long as there is no change in Section 1445 of the
Internal Revenue Code of 1986, as amended (the 'Code'), the Treasury Regulations
promulgated thereunder, or the published interpretations of the Internal Revenue
Service with respect thereto occurring after the date hereof (a 'Change in
Law'), EOP shall not withhold, and shall not cause to be withheld, any tax
pursuant to Section 1445 of the Code in respect of the Merger Consideration to
be paid to PGGM pursuant to the Merger. In the event that EOP believes that a
Change in Law has occurred, it shall deliver written notice thereof to PGGM. In
the event that PGGM shall deliver to EOP an opinion of nationally recognized tax
counsel reasonably satisfactory to EOP to the effect that, taking into account
the Change in Law, EOP is not required to withhold any amount of federal tax
with respect to any portion of the Merger Consideration payable to PGGM under
the Merger Agreement, then the obligation of EOP set forth in the first sentence
of this subparagraph (a) shall continue in effect.

                  (b) (i) EOP shall designate distributions paid by EOP to its
shareholders that have a record date during 2000 prior to the Closing Date as
'capital gain dividends' (as defined in Section 857(b)((3)(C)) of the Code) in
an amount equal to the lesser of (A) the distributions paid by EOP to its
shareholders that have a record date during 2000 prior to the Closing Date
(reduced by any amount designated by EOP pursuant to Section 858(a) of the Code
and the Treasury Regulations thereunder as being paid during 1999), or (B) the
amount of gain that is recognized by EOP during the period commencing on January
1, 2000 and ending on the date prior to the Closing Date with respect to the
disposition of 'United States real property interests' (as defined for purposes
of Section 897 of the Code) and that is otherwise eligible for designation as a
'capital gain dividend' under Section 857(b)(3)(C) of the Code, and (ii) it
shall cause the Form 1099s to be delivered to PGGM and the other EOP
shareholders with respect to the year 2000 to be prepared in a manner consistent
with the foregoing designation; PROVIDED, HOWEVER, that EOP makes no
representation or warranty to PGGM that the aforesaid designation will be
respected for federal income tax purposes and that EOP in no event shall have
any liability to PGGM by reason of a recharacterization by the Internal Revenue
Service of distributions paid by EOP to PGGM during or

                                      -3-


with respect to 2000 as 'capital gain dividends' or as otherwise including
income attributable to the disposition of 'United States real property
interests.' EOP also agrees not to withhold from amounts otherwise distributable
to PGGM any tax pursuant to Section 1445 attributable to 'capital gains
dividends' (within the meaning of Section 857(b)(3)(C) of the Code) distributed
by EOP to its shareholders in 1999.

                  (c) Upon request from PGGM made from time to time (but not
more frequently than once each calendar quarter), EOP shall endeavor to deliver
to PGGM within fifteen (15) business days after the request therefor a statement
(based upon reasonable inquiry) to the effect that, to the knowledge of EOP, EOP
qualifies as a 'domestically controlled REIT' (within the meaning of Section
897(h)(4)(B) of the Code) if such statement in fact would be true when made. For
purposes of such statement, reasonable inquiry shall include review of all
Schedule 13D and 13G filings made under the Exchange Act with the SEC with
respect to EOP during the lesser of the five calendar years preceding the date
of the statement or the period commencing July 1, 1997, all IRS Form 1042
filings made by or on behalf of EOP with respect to each of the five taxable
years preceding the date of the statement (or if shorter, the period commencing
July 1, 1997), the list of EOP's registered shareholders as of a date within 60
days of such statement (and to the extent reasonably available, as of a date
within 60 days of the end of each of the preceding five calendar years (or if
shorter, each of the calendar years commencing with 1997)), a report obtained by
EOP from a shareholders tracking service within 60 days of such statement (and
any similar reports in the possession of EOP or otherwise reasonably available
to EOP providing information as of a date within 60 days of the end of each of
the five preceding calendar years (or if shorter, each of the calendar years
commencing with 1997)), and a list of 'non-objecting beneficial owners' of
shares of EOP obtained as of a date within 60 days of such statement (and to the
extent reasonably available, as of a date within 60 days of the end of each of
the preceding five calendar years (or if shorter, each of the calendar years
commencing with 1997)). Such statement shall be accompanied by copies of the
information that has been obtained or relied upon by EOP for purposes of such
statement, PROVIDED THAT PGGM shall have executed an agreement with EOP to treat
such information as confidential and to use such information solely for the
purposes of evaluating the accuracy of such statement. In the event that EOP
should determine in good faith that it cannot provide to PGGM the requested
statement for any reason, EOP shall notify PGGM of such conclusion and the facts
that cause it to be unable to render such statement. In addition to, and without
limiting, the foregoing, in the event that the General Counsel of EOP shall have
actual knowledge that more than 40 percent, by fair market value, of the
outstanding equity interests of EOP are owned directly or indirectly by 'foreign
persons' (as that term is used for purposes of Section 897(h)(4)(B) of the
Code), EOP shall provide written notice thereof (together with a summary of the
relevant facts) to PGGM, PROVIDED THAT the only duty of inquiry of EOP shall be
as set forth in the first sentence of this subparagraph (c).

                                      -4-


                  (d) In the event that EOP shall make any distributions to PGGM
that it concludes in good faith would be subject to withholding of tax pursuant
to the last sentence of Section 1445(e)(3) of the Code and any Treasury
Regulations promulgated with respect thereto, EOP shall provide such reasonable
cooperation as PGGM may request in applying to the Internal Revenue Service for
a 'withholding certificate' that would reduce or eliminate the requirement for
such withholding; PROVIDED, HOWEVER, that PGGM shall be responsible for the
preparation and submission of the application for such withholding certificate
and that EOP shall not be precluded from withholding such tax unless and until a
'withholding certificate' is obtained (in which event EOP would not withhold tax
that, under the express terms of the 'withholding certificate,' is not required
to be withheld). In addition, in the event that PGGM shall provide to EOP an
opinion of nationally recognized tax counsel reasonably satisfactory to EOP to
the effect that EOP is not required pursuant to Section 1445(e)(3) of the Code
and any Treasury Regulations promulgated with respect thereto to withhold any
amount of federal tax with respect to any portion a distribution to PGGM, EOP
shall not withhold any such tax unless it shall conclude in good faith that a
Change in Law has occurred after the date of such opinion, in which event EOP
shall provide written notice thereof to PGGM. Thereafter, the preceding sentence
would not apply unless PGGM delivers an opinion of nationally recognized tax
counsel reasonably satisfactory to EOP reconfirming the original opinion, after
taking into account the Change in Law.

                  (e) The obligations of EOP set forth in subparagraphs (c) and
(d) shall terminate at such time as PGGM owns less than the lesser of (i) one
percent (1%) of the issued and outstanding EOP Common Shares or (ii) the number
of EOP Common Shares issued to PGGM in the Merger.

                  (f) PGGM agrees that, effective as of the Effective Time of
the Merger, all agreements and undertakings previously entered into by
Cornerstone or any Cornerstone Subsidiary with respect to tax matters,
including, without limitation, agreements restricting the sale or other
disposition of one or more assets owned by Cornerstone, Cornerstone Partnership,
or any Subsidiary of either Cornerstone or Cornerstone Partnership shall
terminate for events or transactions occurring after the Effective Time of the
Merger, and that neither EOP, EOP Partnership nor any Subsidiaries of either EOP
or EOP Partnership shall have any obligation or liability thereunder for events
or transactions occurring following the Effective Time of the Merger. Without
limiting the foregoing, such termination shall include the agreements of
Cornerstone and Cornerstone Partnership set forth in the letter dated June 22,
1998 from Cornerstone and Cornerstone Partnership to PGGM, the undertakings with
respect to tax matters set forth in the Amended and Restated Registration Rights
and Voting Agreement dated as of December 16, 1998 by and among Cornerstone,
PGGM, and Dutch Institutional Holding Company, Inc. (THE 'REGISTRATION RIGHTS
AGREEMENT'), and the policy of Cornerstone with

                                      -5-


respect to One Norwest Center, Denver, Colorado (and any properties acquired in
exchange therefor) adopted by its Board of Directors at a meeting on August 13,
1997.

SECTION 5.        CONSENT TO TRANSFER

                  To the extent required by any mortgage, pledge, security
agreement, deed of trust or other agreement or instrument entered into by
Cornerstone or any of its Affiliates with or for the benefit of PGGM, including,
without limitation, the agreements listed in item 5 on EXHIBIT A attached hereto
(collectively, the 'INSTRUMENTS'), PGGM agrees and acknowledges that, subject to
and effective as of the Effective Time of the Merger, without any further action
by Cornerstone, EOP, PGGM or any other party thereto or beneficiary thereof,
PGGM hereby consents to the transfer to EOP and its Affiliates as a result of
the Mergers and other transactions contemplated by the Merger Agreement of the
beneficial ownership interest of any of the Affiliates of Cornerstone who are a
party to the Instruments and to each other matter thereunder with respect to
which PGGM's consent is required in connection with the Mergers and other
transactions contemplated by the Merger Agreement.

SECTION 6.        REGISTRATION RIGHTS AGREEMENT

                  PGGM and EOP hereby agree and acknowledge that, subject to and
effective as of the Effective Time of the Merger, without any further action by
Cornerstone, EOP or PGGM, EOP and PGGM shall be bound by the Registration Rights
Agreement as the same is amended as follows:

                  (a) From and after the Effective Time of the Merger, (i) all
references in the Registration Rights Agreement to the 'Company' shall be deemed
to be references to EOP; (ii) all references therein to DIHC shall be deleted;
(iii) the references to 'that together own 25% or more of the issued and
outstanding Common Stock' in Sections 1.2(iii) and 1.2(iv) shall be deleted;
(iv) all references therein to 'Common Stock' shall refer to the EOP Common
Shares, (v) the 'Initial Percentage' shall mean 12% of the issued and
outstanding Common Stock; (vi) the 'Standstill Period' shall mean, with respect
to any Holder, a period of time commencing on the Effective Time of the Merger
and terminating ninety (90) days after the first date following the election of
PGGM's designees to EOP's Board of Trustees that no Trustee designated by PGGM
pursuant to Section 7 of this Voting Agreement remains a Trustee of EOP; and
(vii) all references therein to 'Units' shall refer to EOP OP Units.

                  (b) Section 2 shall be deleted in its entirety and all
references to Section 2 in the Registration Rights Agreement shall be deleted.

                                      -6-


                  (c) Section 3.1(a) shall be amended to delete the reference to
the specified Cornerstone Registration Statement and to cause the first line to
read as follows: 'Within 20 days after the request of PGGM following the
Effective Time of the Merger.'

                  (d) Section 7 shall be deleted in its entirety and all
references to Section 7 in the Registration Rights Agreement shall be deleted.

                  (e) Section 8 shall be amended as follows: (i) the reference
to 'that together with its Affiliates owns 25% or more of the issued and
outstanding shares of Common Stock' in Section 8 shall be deleted, and (ii) the
reference to 'Section 78.140 of the Nevada General Corporation Law' shall refer
to Section 2-419 of the Maryland General Corporation Law.

                  (f) Section 9 shall be amended as follows: (i) deleting 'and'
after the end of clause (I), (ii) adding 'and' after the end of clause (II), and
(iii) adding a new clause (III) as follows: '(III) by the Company in connection
with a Business Combination to which the Company is a party.'

                  (g) Section 11 shall be amended to refer to the address of EOP
set forth in the Merger Agreement.

                  (h) Sections 12 and 13 shall be deleted.

SECTION 7.        TRUSTEES

                  The trustees of EOP following the Merger shall consist of the
trustees of EOP immediately prior to the Effective Time of the Merger, who shall
continue to serve for the balance of their unexpired terms or their earlier
death, resignation or removal, together with John S. Moody, William Wilson III
and Jan van der Vlist, each of whom shall, no later than the third business day
after the Effective Time of the Merger, become a trustee with terms expiring in
2002, 2003 and 2003, respectively. Upon the expiration of the terms of Mr. van
der Vlist in 2003 and 2006, so long as PGGM and its Affiliates continue to own
in the aggregate 21,000,000 (as adjusted for stock splits, reverse stock splits,

                                      -7-


stock dividends and similar actions) or more of the issued and outstanding EOP
Common Shares at all times up to the meeting of shareholders at which trustees
are being elected in such years, EOP shall take all action necessary to nominate
Mr. van der Vlist for re-election as a trustee of EOP for an additional
three-year term at any special or annual meeting of shareholders at which
trustees are being elected (or in connection with a written consent in lieu of a
meeting pursuant to which trustees are proposed to be elected). In the event
that Mr. Van der Vlist shall fail to stand for re-election as aforesaid for any
reason in either 2003 or 2006 or in the event of his earlier death or
resignation, and so long as PGGM and its Affiliates continue to own in the
aggregate 21,000,000 (as adjusted for stock splits, reverse stock splits, stock
dividends and similar actions) or more of the issued and outstanding EOP Common
Shares at such time, EOP shall take all action necessary to nominate a
replacement designated by PGGM, which replacement shall be subject to the
approval of EOP if such replacement is not an officer, director or employee of
PGGM, for election or re-election as a trustee of EOP for an additional
three-year term at any special or annual meeting of shareholders at which
trustees are being elected (or in connection with a written consent in lieu of a
meeting pursuant to which trustees are proposed to be elected) or, in the case
of a vacancy, at a meeting of the Board of Trustees called for such purpose.
Except as expressly provided above in this Section 7, following their election
as trustees, such persons shall serve for their designated terms, subject to
their earlier death, resignation or removal.

SECTION 8.        CERTAIN AGREEMENTS

                  PGGM represents and warrants to EOP, EOP Partnership and WCP
that (a) the only pending claims asserted against PGGM or Robert T. Sorrentino,
Craig W. Johnston or Barrington H. Branch (the 'Individuals') under the
Indemnity Agreement, dated as of October 27, 1997, as thereafter amended, among
DIHC Holding Company, Inc., PGGM and Cornerstone (the 'Indemnity Agreement') or
any of the agreements listed in items 1, 2, 3 and 4 on EXHIBIT A attached hereto
(collectively, the 'Purchase Agreements') are (i) the Western Litigation (as
defined in the Indemnity Agreement) and (ii) the Massachusetts state tax claim
previously disclosed to EOP in writing (the 'Massachusetts Tax Claim'), and (b)
to its knowledge after reasonable inquiry, there is no basis for any further
claim, obligation, or liability of PGGM or any of the Individuals under the
Indemnity Agreement or any of the Purchase Agreements. EOP, EOP Partnership and
WCP hereby agree and acknowledge that, subject to and effective as of the
Effective Time of the Merger, without any further action by EOP, EOP
Partnership, WCP or PGGM, PGGM and the Individuals shall be released and
discharged from any and all claims, obligations or liabilities under the
Indemnity Agreement and the Purchase Agreements, including, without limitation,
with respect to or in connection with the Massachusetts Tax Claim (collectively,
the 'Released Claims'), EXCEPT for (x) any claims, obligations or liabilities
with respect to or in connection with the Western Litigation and (y) any claims,
obligations or liabilities a basis for which PGGM has or would have had
knowledge after reasonable inquiry as of the Effective Time (collectively (x)
and (y) being referred to as the 'Excluded Claims'). From and after the
Effective Time, EOP and EOP Partnership shall indemnify, defend and hold
harmless PGGM from and against any and all cost, claim, liability, damage or
expense (including, without limitation, reasonable attorneys' fees) with respect
to or in connection with the Released Claims and PGGM and the Individuals shall
be obligated under the Indemnity Agreement and the Purchase Agreements to EOP
and EOP Partnership with respect to or in connection with the Excluded Claims.

                                      -8-


SECTION 9.        REPRESENTATIONS AND WARRANTIES OF PGGM

                  PGGM represents and warrants to EOP and EOP Partnership as
follows:

                  (a) PGGM has the legal capacity, power, authority and right
(contractual or otherwise) to execute and deliver this Agreement and to perform
its obligations hereunder. PGGM has obtained all consents of third parties
necessary to enter into this Agreement and to perform its obligations hereunder,
including, without limitation, the amendments to the Registration Rights
Agreement.

                  (b) This Agreement has been duly executed and delivered by
PGGM and constitutes a valid and binding obligation of PGGM enforceable against
PGGM in accordance with its terms, subject to applicable bankruptcy, insolvency,
moratorium or other similar laws relating to creditors rights and general
principles of equity.

                  (c) The execution and delivery of this Agreement and the
consummation of the transactions herein contemplated will not conflict with or
violate any court order, judgment or decree applicable to PGGM, or conflict with
or result in any breach of or constitute a default (or an event which with
notice or lapse of time or both would become a default) under any contract or
agreement to which PGGM is a party or by which PGGM is bound or affected, which
conflict, violation, breach or default would materially and adversely affect
PGGM's ability to perform any of its obligations under this Agreement.

                  (d) Subject to any required filings under the Securities
Exchange Act of 1934 (the ' '34 Act'), PGGM is not required to give any notice
or make any report or other filing with any governmental authority in connection
with the execution or delivery of this Agreement or the performance of PGGM's
obligations hereunder and no waiver, consent, approval or authorization of any
governmental or regulatory authority or any other person or entity is required
to be obtained by PGGM for the performance of PGGM's obligations hereunder,
other than where the failure to make such filings, give such notices or obtain
such waivers, consents, approvals or authorizations would not materially and
adversely affect PGGM's ability to perform this Agreement.

                  (e) Cornerstone Common Shares set forth opposite PGGM on
SCHEDULE 1 hereto are the only Cornerstone Common Shares or other Cornerstone or
Cornerstone Partnership securities owned beneficially or of record by PGGM or
over which it exercises voting control.

                                      -9-


SECTION 10.       REPRESENTATIONS AND WARRANTIES OF EOP AND EOP PARTNERSHIP

                  EOP and EOP Partnership represent and warrant to PGGM as
follows:

                  (a) Each of EOP and EOP Partnership has the legal capacity,
power, authority and right (contractual or otherwise) to execute and deliver
this Agreement and to perform its obligations hereunder. Each of EOP and EOP
Partnership has obtained all consents of third parties necessary to enter into
this Agreement and to perform its obligations hereunder.

                  (b) This Agreement has been duly executed and delivered by EOP
and EOP Partnership and constitutes a valid and binding obligation of EOP and
EOP Partnership enforceable against them in accordance with its terms, subject
to applicable bankruptcy, insolvency, moratorium or other similar laws relating
to creditors rights and general principles of equity.

                  (c) The execution and delivery of this Agreement and the
consummation of the transactions herein contemplated will not conflict with or
violate any court order, judgment or decree applicable to EOP or EOP
Partnership, or conflict with or result in any breach of or constitute a default
(or an event which with notice or lapse of time or both would become a default)
under any contract or agreement to which EOP or EOP Partnership is a party or by
which EOP or EOP Partnership is bound or affected, which conflict, violation,
breach or default would materially and adversely affect EOP or EOP Partnership's
ability to perform any of its obligations under this Agreement.

                  (d) Subject to any required filings under the Securities
Exchange Act of 1934 (the ' '34 Act'), neither EOP nor EOP Partnership is
required to give any notice or make any report or other filing with any
governmental authority in connection with the execution or delivery of this
Agreement or the performance of its obligations hereunder and no waiver,
consent, approval or authorization of any governmental or regulatory authority
or any other person or entity is required to be obtained by EOP or EOP
Partnership for the performance of its obligations hereunder, other than where
the failure to make such filings, give such notices or obtain such waivers,
consents, approvals or authorizations would not materially and adversely affect
its ability to perform this Agreement.

SECTION 11.       FURTHER ASSURANCES

                  PGGM shall make such filings as may be required from time to
time under the '34 Act. The parties hereto shall, upon request by the other, do,
execute, acknowledge, deliver, record, re-record, file, re-file, register and
re-register any and all such further acts, deeds, conveyances, security
agreements, pledge agreements, mortgages, deeds of trust, trust deeds,
assignments, estoppel certificates, financing

                                      -10-


statements and continuation thereof, termination statements, notices of
assignment, transfers, certificates, assurances and other instruments as the
requesting party reasonably may request from time to time in order to effectuate
the purposes of this Agreement, including, without limitation, to perfect and
maintain the validity, effectiveness and priority of any of the Instruments and
the liens and security interests intended to be created thereby and better to
assure, convey, grant, assign, transfer, preserve, protect and confirm unto PGGM
the rights granted now or hereafter intended to be granted under the
Instruments.

SECTION 12.       DESCRIPTIVE HEADINGS

                  The descriptive headings herein are inserted for convenience
only and are not intended to be part of or to affect the meaning or
interpretation of this Agreement.

SECTION 13.       COUNTERPARTS

                  This Agreement may be executed in counterparts, each of which
when so executed and delivered shall be an original, but all of such
counterparts shall together constitute one and the same instrument.

SECTION 14.       ENTIRE AGREEMENT; ASSIGNMENT

                  This Agreement (i) constitutes the entire agreement and
supersedes all prior agreements and understandings, both written and oral, among
the parties hereto with respect to the subject matter hereof and (ii) shall not
be assigned by operation of law or otherwise; PROVIDED, HOWEVER, following the
Effective Time, this Agreement may be assigned by EOP in the same circumstances
as under the Registration Rights Agreement.

SECTION 15.       NOTICES.

                  All notices, requests, claims, demands and other
communications under this Agreement shall be in writing and shall be delivered
personally, sent by overnight courier (providing proof of delivery) to the
parties or sent by telecopy (providing confirmation of transmission) at the
following addresses or telecopy numbers (or at such other address or telecopy
number for a party as shall be specified by like notice):

                                      -11-


                      (a)   if to EOP or EOP Partnership, to:

                                 Equity Office Properties Trust
                                 EOP Operating Limited Partnership
                                 Two N. Riverside Plaza
                                 Chicago, IL 60606
                                 Attention: President
                                            Chief Counsel
                                 Fax No.: (312) 559-5021

                            with a copy to:

                                 Hogan & Hartson L.L.P.
                                 555 Thirteenth Street, N.W.
                                 Washington, D.C. 20004-1109
                                 Attention: J. Warren Gorrell, Jr., Esq.
                                            George P. Barsness, Esq.
                                 Fax No.: (202) 637-5910

                      (b)   if to Cornerstone or Cornerstone Partnership, to:

                                    Tower 56
                                    125 East 56th Street, 6th Floor New
                                    York, NY 10022 Attention: President
                                    Fax No.: (212) 605-7100

                            with a copy to:

                                    King & Spalding
                                    191 Peachtree Street
                                    Atlanta, GA 30303-1763
                                    Attention: William B. Fryer, Esq.
                                    Fax No.: (404) 572-5100

                      (c)   if to PGGM, to:

                                    Stichting Pensioenfonds voor de Gezondheid,
                                       Geestelijke en Maatschappelijke Belangen
                                    Utrechtseweg 44
                                    3714 HD Zeist
                                    The Netherlands
                                    Attention: Anneke C. van de Puttelaar
                                    Fax No.: 011 3130 696 3388

                                      -12-


                            with a copy to:

                                    Richards & O'Neil, LLP
                                    885 Third Avenue
                                    New York, NY 10022
                                    Attention: Ann F. Chamberlain, Esq.
                                    Fax No.: (212) 750-9022


All notices shall be deemed given only when actually received.


SECTION 16.       GOVERNING LAW; CONSENT TO JURISDICTION; WAIVER OF JURY TRIAL

                  (a) This Agreement shall be governed by and construed in
accordance with the laws of the State of Maryland without regard to the
principles of conflicts of laws thereof.

                  (b) PGGM hereby submits and consents to non-exclusive personal
jurisdiction in any action, suit or proceeding arising out of this Agreement or
the transactions contemplated hereby in a federal court located in the State of
Maryland or in a Maryland state court. Any process, summons, notice or document
delivered by mail to the address set forth in Section 15 hereof shall be
effective service of process for any action, suit or proceeding in any Maryland
state court or any federal court located in the State of Maryland with respect
to any matters to which PGGM has submitted to jurisdiction in this Section 16.
PGGM irrevocably and unconditionally waives any objection to the laying of venue
of any action, suit or proceeding arising out of this Agreement or the
transactions contemplated hereby in any Maryland state court or any federal
court located in the State of Maryland, and hereby irrevocably and
unconditionally waives and agrees not to plead or claim in any such court that
any such action, suit or proceeding brought in any such court has been brought
in an inconvenient forum. PGGM IRREVOCABLY WAIVES TRIAL BY JURY IN ANY ACTION,
SUIT OR PROCEEDING WITH RESPECT TO THIS AGREEMENT.

SECTION 17.       SPECIFIC PERFORMANCE

                  The parties hereto agree that if any of the provisions of this
Agreement were not performed in accordance with their specific terms or were
otherwise breached, irreparable damage would occur, no adequate remedy at law
would exist and damages would be difficult to determine, and that the parties
shall be entitled to specific performance of the terms hereof, in addition to
any other remedy at law or equity. Nothing contained herein shall release any
party from any liability

                                      -13-


arising from any breach of any of its representations, warranties, covenants or
agreements in this Agreement.

SECTION 18.       CAPACITY OF PGGM AND ITS OFFICERS, DIRECTORS AND EMPLOYEES.

                  PGGM has executed this Agreement solely in its capacity as a
stockholder of Cornerstone. Without limiting the foregoing, nothing in this
Agreement shall limit or affect any actions taken by any officer, director or
employee of PGGM in his capacity as an officer, director, employee or manager of
Cornerstone in connection with the exercise of Cornerstone's rights under the
Merger Agreement.



                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK.]


                                      -14-


                  IN WITNESS WHEREOF, the parties hereto have duly executed and
delivered this Voting Agreement, or have caused this Voting Agreement to be duly
executed and delivered in their names and on their behalf, as of the date first
written above.


                                     EQUITY OFFICE PROPERTIES TRUST

                                     By:   /s/ Stanley M. Stevens
                                     ----------------------------
                                     Name:  Stanley M. Stevens
                                     Title: Executive Vice President
                                            and Chief Legal Counsel


                                     EOP OPERATING LIMITED PARTNERSHIP

                                     By:  Equity Office Properties Trust, its
                                          general partner

                                     By:   /s/ Stanley M. Stevens
                                     ----------------------------
                                     Name:  Stanley M. Stevens
                                     Title: Executive Vice President
                                            and Chief Legal Counsel


                                     WCP SERVICES, INC.



                                     By:   /s/ John S. Moody
                                     ----------------------------
                                     Name:  John S. Moody
                                     Title: President


                                     PENSIOENFONDS VOOR DE
                                     GEZONDHEID, GEESTELIJKE EN
                                     MAATSCHAPPELIJKE BELANGEN


                                     By: /s/ Jan H.W.R. van der Vlist
                                        ----------------------------------------
                                     Name:  Jan H.W.R. van der Vlist
                                     Title: Attorney-in-Fact


                                      -15-





                                                                      SCHEDULE 1



                           # OF SHARES
     NAME OF                    OF
   RECORD AND              CORNERSTONE
   BENEFICIAL                 COMMON                                    TERMS OF
     OWNER                    STOCK               PLEDGEE                PLEDGE
                                                             

PGGM                        45,779,703         Not Applicable         Not Applicable



                                      -16-