Letter Agreement - Wolters Kluwer U.S. Corp. and Plenum Publishing Corp.

                [LETTERHEAD OF WOLTERS KLUWER U.S. CORPORATION]

Bruce C. Lenz
Executive Vice President
Chief Financial Officer

                                  June 10, 1998

Mr. Martin E. Tash
President
Plenum Publishing Corporation
233 Spring Street 
New York, New York 10013

Dear Mr. Tash:

      In consideration of the execution today of an agreement and plan merger by
and among our wholly owned subsidiary Kluwer Boston, Inc. and Plenum Publishing
Corporation which agreement is intended to result in the acquisition of all the
shares of Plenum Publishing Corporation at 73.50 per share for a total purchase
of approximately $258 million dollars, we hereby agree that we will fund the
obligations of our subsidiary and of PPC Acquisition Corp., our indirect
subsidiary, through available cash balances and existing bank credit lines of
Wolters Kluner nv. We hereby represent and warrant that there are available cash
balances and exiting bank credit lines which will enable us to meet this
obligation.

                                           Yours sincerely,                     
                                           
                                           WOLTERS KLUWER U.S. CORPORATION

                                           
                                           By:  /s/ Bruce C. Lenz
                                                ---------------------------
                                                Bruce C. Lenz
                                                Executive Vice President and
                                                Chief Financial Officer