Confidentiality Agreement - Wolters Kluwer US Corp. and Plenum Publishing Corp.


                                                                   April 8, 1998






Mr. Bruce Lenz
Executive Vice President & CFO (WK USA)
Wolters Kluwer US Corporation
161 North Clark Street
48th Flr.
Chicago, IL   60601


Dear Mr. Lenz:

        You have requested information from Plenum Publishing Corporation (the
'Company') in connection with your consideration of a possible acquisition by
you of the Company (an 'Acquisition Transaction'). As a condition to our
furnishing such information to you, we are requiring that you agree, as set
forth below, to treat confidentially such information, whether written or oral,
and any other information that the Company, its agents or its representatives
(including attorneys and financial advisors) furnishes to you or your directors,
officers, employees, agents, advisors, prospective bank or institutional
lenders, affiliates or representatives of your agents, advisors or prospective
lenders (all of the foregoing collectively referred to as 'your
Representatives'), whether furnished before or after the date of this letter,
and all notes, analyses, compilations, studies or other documents, whether
prepared by you or others, which contain or otherwise reflect such information
(collectively, the 'Evaluation Material').

        The term 'Evaluation Material' does not include information which (i)
becomes generally available to the public other than as a result of a disclosure
by you or your Representatives, (ii) was available to you on a non-confidential
basis prior to its disclosure to you by the Company, its representatives or its
agent, or (iii) becomes available to you on a non-confidential basis from a
source other than the Company 




('Source'), its representatives or its agents, provided that such Source is not,
to your knowledge after due inquiry, bound by a confidentiality agreement with
the Company, its representatives or its agents or otherwise, to your knowledge
after due inquiry, prohibited from transmitting the information to you or your
Representatives by a contractual, legal or fiduciary obligation and provided
that the existence of such Source is not disclosed to you in the Evaluation
Material.

        It is understood that you may disclose any of the Evaluation Material to
those of your Representatives who require such material for the purpose of
evaluating a possible Acquisition Transaction (provided that such
Representatives shall be informed by you of the confidential nature of the
Evaluation Material). You agree that the Evaluation Material will be kept
confidential by you and your Representatives and, except with the specific prior
written consent of the Company or as expressly otherwise permitted by the terms
hereof, will not be disclosed by you or your Representatives. You further agree
that you and your Representatives will not use any of the Evaluation Material or
any information obtained from the Evaluation Material for any reason or purpose
other than to evaluate a possible Acquisition Transaction.

        Without the prior written consent of the Company, you and your
Representatives will not disclose to any person (1) the fact that the Evaluation
Material has been made available to you or that you have inspected any portion
of the Evaluation Material, (2) the fact that any discussions or negotiations
are taking place concerning a possible Acquisition Transaction, or (3) any of
the terms, conditions or other facts with respect to any possible Acquisition
Transaction, including the status thereof, unless and only to the extent that
such disclosure (after making reasonable efforts to avoid such disclosure and
after advising and consulting with the Company about your intention to make, and
the proposed contents of such disclosure) is, in the opinion of your counsel,
required by applicable United States securities laws. The term 'person' as used
in this letter shall be broadly interpreted to include without limitation any
corporation, company, partnership and individual.

        In the event that you or any of your Representatives are requested or
required (by oral questions, interrogatories, requests for information or
documents, subpoena, Civil Investigative Demand or similar process) to disclose
any of the Evaluation Material, it is agreed that you or such Representative, as
the case may be, will provide the Company with prompt notice of such request(s)
so that it may seek an appropriate protective order or other appropriate remedy
and/or waive your or such Representative's compliance with the provisions of
this Agreement. In the event that such protective order or other remedy is not
obtained, or that the Company grants a waiver hereunder, you or such
Representative may furnish that portion (and only that portion) of the
Evaluation Material which, in the written opinion of your counsel, you are
legally compelled to disclose and will exercise your best efforts to obtain
reliable assurance that confidential treatment will




be accorded any Evaluation Material so furnished.

        In addition, you hereby acknowledge that you are aware (and that your
Representatives who are apprised of this matter have been or will be advised)
that the United States securities laws restrict persons with material non-public
information about a company obtained directly or indirectly from that company
from purchasing or selling securities of such company, or from communicating
such information to any other person under circumstances in which it is
reasonably foreseeable that such person is likely to purchase or sell such
securities.

        You agree that for a period of one year from the date of this letter
agreement, neither you nor any of your affiliates, alone or with others, will in
any manner (1) acquire, agree to acquire, or make any proposal (or request
permission to make any proposal) to acquire any securities (or direct or
indirect rights, warrants or options to acquire any securities) or property of
the Company (other than property transferred in the ordinary course of the
Company's business), unless such acquisition, agreement or making of a proposal
shall have been expressly first approved (or in the case of a proposal,
expressly first invited) by the Company's Board of Directors, (2) except at the
specific written request of the Company, propose to enter into, directly or
indirectly, any merger or business combination involving the Company or any of
its subsidiaries, (3) solicit proxies from shareholders of the Company or
otherwise seek to influence or control the management or policies of the Company
or any of its affiliates, (4) form, join or in any way participate in a 'group'
(within the meaning of Section 13(d)(3) of the Securities Exchange Act of 1934)
with respect to any voting securities of the Company or any of its subsidiaries,
(5) otherwise act, alone or in concert with others, to seek to control or
influence the management, Board of Directors or policies of the Company, (6)
disclose any intention, plan or arrangement inconsistent with the foregoing or
(7) assist, advise or encourage (including by knowingly providing or arranging
financing for that purpose) any other person in doing any of the foregoing. You
also agree during such period not to (1) request the Company (or its directors,
officers, employees or agents), directly or indirectly, to amend or waive any
provisions of this paragraph (including this sentence), or (2) take any action
which might require the Company to make a public announcement regarding the
possibility of a business combination, merger or extraordinary transaction. You
hereby represent that neither you nor your affiliates beneficially own any
shares of the Common Stock of the Company.

        You agree that, without the prior written consent of the Company,
neither you nor those of your Representatives who are aware of the Evaluation
Material and/or the possibility of an Acquisition Transaction will initiate or
cause to be initiated or maintain (other than through Salomon Brothers Inc and
Smith Barney Inc. doing business as 'Salomon Smith Barney') any communications
with any officer, director, agent or employee of the Company concerning the
Company's business, operations, prospects or 




finances or the Evaluation Material or any possible Acquisition Transaction.
Moreover, you further agree that Salomon Smith Barney will arrange for
appropriate contacts for due diligence purposes and that all (a) communications
regarding any possible Acquisition Transaction, (b) requests for additional
information, (c) requests for facility tours or management meetings and (d)
discussions or questions regarding procedures, will be submitted or directed to
Salomon Smith Barney.

        You agree that, for a period of six months from the date hereof, without
the prior written consent of the Company, you will not solicit or cause to be
solicited any person employed by the Company or its subsidiaries or affiliates
at any time during such period and to whom you had been directly or indirectly
introduced or otherwise had contact with during or as the result of your review
of the Evaluation Material or your consideration of an Acquisition Transaction.

        You will promptly upon the written request of the Company deliver to the
Company all documents or other matter furnished by the Company to you or your
Representatives constituting Evaluation Material, together with all copies
thereof in the possession of you or your Representatives. In the event of such
request, all other documents or other matter constituting Evaluation Material,
or any analyses, compilations, studies or other documents containing or
reflecting your use of the Evaluation Material, in the possession of you or your
Representatives will be destroyed, with any such destruction confirmed by you in
writing to the Company.

        Although you understand that the Company has endeavored to include in
the Evaluation Material information known to it which it believes to be relevant
for the purpose of your investigation, you further understand that neither the
Company nor its agents or its representatives makes any representation or
warranty, express or implied, as to the accuracy or completeness of the
Evaluation Material. You agree that neither the Company nor its officers,
directors, stockholders, owners, affiliates, agents or representatives shall
have any liability to you or any of your Representatives or any other person
resulting from the use of the Evaluation Material by you or such
representatives. Only those representations and warranties that may be made to
you or affiliates in definitive written agreement for an Acquisition
Transaction, when, as and if executed and subject to such limitations and
restrictions as may be specified therein, shall have any legal effect, and you
agree that if you determine to engage in an Acquisition Transaction such
determination will be based solely on the terms of such written agreement and on
your own investigation, analysis and assessment of the business to be acquired.

        You also hereby agree that no contract or agreement providing for an
Acquisition Transaction will be deemed to exist between you and the Company
and/or the owners or stockholders of the Company unless and until a definitive
written agreement has been signed, executed and delivered by you and the Company
and/or




such owners or stockholders. Moreover, unless and until such a definitive
written agreement is entered into, executed and delivered, none of the Company,
its stockholders or its affiliates or you will be under any legal obligation of
any kind whatsoever with respect to any Acquisition Transaction except for the
matters specifically agreed to in this Agreement. You also hereby waive, in
advance, any claims (including, without limitation, claims for breach of
contract) in connection with any Acquisition Transaction or any other
transaction unless and until such a definitive, written agreement is entered
into, executed and delivered. For the purposes of this paragraph, a 'definitive
written agreement' does not include an executed letter of intent or any other
preliminary written agreement, nor does it include any written or oral
acceptance of any offer or bid.

        You understand that (a) the Company shall be free to conduct any process
with respect to a possible Acquisition Transaction as the Company in its sole
discretion shall determine (including, without limitation, by negotiating with
any prospective party and entering into a definitive written agreement without
prior notice to you or any other person), (b) any procedures relating to such
Acquisition Transaction may be changed at any time without notice to you or any
other person and (c) you shall not have any claim whatsoever against the Company
or Salomon Smith Barney or any of their respective directors, officers,
stockholders, owners, affiliates, agents or representatives, arising out of or
relating to any possible or actual Acquisition Transaction (other than those as
against parties to a definitive written agreement with you in accordance with
the terms thereof).

        You hereby agree to indemnify and hold harmless the Company from any
damage, loss, cost or liability arising out of or resulting from any
unauthorized use or disclosure by you or your Representatives of the Evaluation
Material or any information obtained from the Evaluation Material.

        You also acknowledge that money damages would be both incalculable and
an insufficient remedy for any breach of this Agreement by you or your
Representatives and that any such breach would cause the Company irreparable
harm. Accordingly, you agree that in the event of any breach of threatened
breach of this Agreement, the Company, in addition to any other remedies at law
or in equity it may have, shall be entitled, without the requirement of posting
a bond or other security, to equitable relief, including injunctive relief and
specific performance.

        You also hereby irrevocably and unconditionally consent to submit to 
the exclusive jurisdiction of the courts of the State of New York and of the 
United States of America located in the City of New York for any actions, 
suits or proceedings arising out of or relating to this Agreement and the 
transactions contemplated hereby (and you agree not to commence any action, 
suit or proceeding relating thereto except in such courts), and further agree 
that service of any process, summons, notice or document by U.S. 




registered mail to your address set forth above shall be effective service of
process for any action, suit or proceeding brought against you in any such
court. You hereby irrevocably and unconditionally waive any objection to the
laying of venue of any action, suit or proceeding arising out of this Agreement
or the transactions contemplated hereby in the courts of the State of New York
or the United States of America located in the City of New York, and hereby
further irrevocably and unconditionally waive and agree 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.

        The agreements set forth in this Agreement may be modified or waived
only by a separate writing signed by the Company and you expressly so modifying
or waiving such agreements.

        It is understood and agreed that no failure or delay by the Company in
exercising any right, power or privilege hereunder shall operate as a waiver
thereof, nor shall any single or partial exercise thereof preclude any other or
further exercise thereof or the exercise of any right, power or privilege
hereunder.

        The invalidity or unenforceability of any provision of this Agreement
shall not affect the validity or enforceability of any other provisions of this
letter agreement, which shall remain in full force and effect.

        This Agreement shall be governed by and construed in accordance with the
laws of the State of New York.




        If you are in agreement with the foregoing, please sign and return one
copy of this letter, which thereupon will constitute our Agreement with respect
to the subject matter hereof.

                                Very truly yours,

                                Plenum Publishing Corporation




                                By   /s/ Katherine A. Brown
                                   ----------------------------
                                     Title: Vice President
                                     Salomon Brothers Inc
                                     Smith Barney Inc.
                                       on behalf of
                                       Plenum Publishing Corporation




Confirmed and agreed to as of 
the date first above written:

Wolters Kluwer U.S. Corporation
-----------------------------------

By /s/ Bruce C. Lenz
   --------------------------------
   Title: Executive Vice President