PLENUM PUBLISHING CORP
SC 14D1, 1998-06-16
PERIODICALS: PUBLISHING OR PUBLISHING & PRINTING
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<PAGE>
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                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                                 SCHEDULE 14D-1
 
 Tender Offer Statement Pursuant to Section 14(d)(1) of the Securities Exchange
                                  Act of 1934
 
                                      and
 
                                 SCHEDULE 13D*
 
                   under the Securities Exchange Act of 1934
 
                         PLENUM PUBLISHING CORPORATION
 
                           (Name of Subject Company)
 
                             PPC ACQUISITION CORP.
 
                              KLUWER BOSTON, INC.
 
                        WOLTERS KLUWER U.S. CORPORATION
                               WOLTERS KLUWER NV
 
                                   (Bidders)
 
                     COMMON STOCK, $.10 PAR VALUE PER SHARE
 
                         (Title of Class of Securities)
 
                            729093104 (COMMON STOCK)
 
                     (CUSIP Number of Class of Securities)
 
                              MR. JEFFREY K. SMITH
                      C/O KLUWER ACADEMIC PUBLISHERS B.V.
                                SPUIBOULEVARD 50
                            3300 A<#>Z</#> DORDRECHT
                                THE NETHERLANDS
 
                         TELEPHONE (011) 31 78 6392283
 
(Name, Address and Telephone Number of Person Authorized to Receive Notices and
                      Communications on Behalf of Bidders)
 
                                    COPY TO:
 
                             Arnold J. Schaab, Esq.
                       Pryor Cashman Sherman & Flynn LLP
                                410 Park Avenue
                            New York, New York 10022
                            Telephone (212) 326-0168
 
                           CALCULATION OF FILING FEE
 
<TABLE>
<CAPTION>
                TRANSACTION VALUATION**                                   AMOUNT OF FILING FEE***
<S>                                                       <C>
                    $258,003,448.50                                              $51,600.69
</TABLE>
 
*   This Statement also constitutes the Statement on Schedule 13D of PPC
    Acquisition Corp., Kluwer Boston, Inc., Wolters Kluwer U.S. Corporation and
    Wolters Kluwer nv filed with respect to the shares of Common Stock, par
    value $.10 per share, of Plenum Publishing Corporation beneficially owned by
    PPC Acquisition Corp., Kluwer Boston, Inc., Wolters Kluwer U.S. Corporation
    and Wolters Kluwer nv.
 
**  For purposes of calculating the filing fee only. This calculation assumes
    the purchase of 3,510,251 shares of common stock, $.10 par value, of Plenum
    Publishing Corporation, at $73.50 net per share in cash.
 
*** The amount of the filing fee, calculated in accordance with Rule 0-11(d) of
    the Securities Exchange Act of 1934, as amended, equals 1/50th of one
    percent of the aggregate value of cash offered by PPC Acquisition Corp. for
    such number of Shares.
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
<PAGE>
 
<TABLE>
<C>                                           <S>                   <C>
            CUSIP NO. 729093104                                        PAGE 2 OF PAGES 12
</TABLE>
 
<TABLE>
<C>        <S>
 
    1.     NAME OF REPORTING PERSONS
           S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
           PPC Acquisition Corp.
 
    2.                     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP                (a) /X/
                                                                                           (b) / /
 
    3.     SEC USE ONLY
 
    4.     SOURCE OF FUNDS
           AF
 
    5.     CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
           PURSUANT TO ITEMS 2(e) OR 2(f)                                                / /
 
    6.     CITIZENSHIP OR PLACE OF ORGANIZATION
           Delaware
 
    7.     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH
           REPORTING PERSON
           536,960 shares of
           Common Stock pursuant to
           the five Stock Purchase Agreements
           each dated as of June 10, 1998(1)
 
    8.     CHECK IF THE AGGREGATE AMOUNT IN ROW (7) EXCLUDES
           CERTAIN SHARES                                                                / /
 
    9.     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (7)
           15.3%
 
   10.     TYPE OF REPORTING PERSON
           CO
</TABLE>
 
(1) The Reporting Person disclaims beneficial ownership of such shares and this
    statement shall not be construed as an admission that the Reporting Person
    is the beneficial owner of any securities covered by this statement.
 
                                       2
<PAGE>
 
<TABLE>
<C>                                           <S>                   <C>
            CUSIP NO. 729093104                                        PAGE 3 OF PAGES 12
</TABLE>
 
<TABLE>
<C>        <S>
 
    1.     NAME OF REPORTING PERSONS
           S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
           Kluwer Boston, Inc.
 
    2.                     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP                (a) /X/
                                                                                           (b) / /
 
    3.     SEC USE ONLY
 
    4.     SOURCE OF FUNDS
           AF
 
    5.     CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
           PURSUANT TO ITEMS 2(e) OR 2(f)                                                / /
 
    6.     CITIZENSHIP OR PLACE OF ORGANIZATION
           Massachusetts
 
    7.     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH
           REPORTING PERSON
           536,960 shares of
           Common Stock pursuant to
           the five Stock Purchase Agreements
           each dated as of June 10, 1998(1)
 
    8.     CHECK IF THE AGGREGATE AMOUNT IN ROW (7) EXCLUDES
           CERTAIN SHARES                                                                / /
 
    9.     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (7)
           15.3%
 
   10.     TYPE OF REPORTING PERSON
           CO
</TABLE>
 
(1) The Reporting Person disclaims beneficial ownership of such shares and this
    statement shall not be construed as an admission that the Reporting Person
    is the beneficial owner of any securities covered by this statement.
 
                                       3
<PAGE>
 
<TABLE>
<C>                                           <S>                   <C>
            CUSIP NOS. 729093104                                       PAGE 4 OF PAGES 12
</TABLE>
 
<TABLE>
<C>        <S>
 
    1.     NAME OF REPORTING PERSONS
           S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
           Wolters Kluwer U.S. Corporation
 
    2.                     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP                (a) /X/
                                                                                           (b) / /
 
    3.     SEC USE ONLY
 
    4.     SOURCE OF FUNDS
           AF
 
    5.     CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
           PURSUANT TO ITEMS 2(e) OR 2(f)                                                / /
 
    6.     CITIZENSHIP OR PLACE OF ORGANIZATION
           Delaware
 
    7.     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH
           REPORTING PERSON
           536,960 shares of Common Stock pursuant to
           the five Stock Purchase Agreements each dated as of
           June 10, 1998(1)
 
    8.     CHECK IF THE AGGREGATE AMOUNT IN ROW (7) EXCLUDES
           CERTAIN SHARES                                                                / /
 
    9.     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (7)
           15.3%
 
   10.     TYPE OF REPORTING PERSON
           CO
</TABLE>
 
(1) The Reporting Person disclaims beneficial ownership of such shares and this
    statement shall not be construed as an admission that the Reporting Person
    is the beneficial owner of any securities covered by this statement.
 
                                       4
<PAGE>
 
<TABLE>
<C>                                           <S>                   <C>
            CUSIP NO. 729093104                                        PAGE 5 OF PAGES 12
</TABLE>
 
<TABLE>
<C>        <S>
 
    1.     NAME OF REPORTING PERSONS
           S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
           Wolters Kluwer nv
 
    2.                     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP                (a) /X/
                                                                                           (b) / /
 
    3.     SEC USE ONLY
 
    4.     SOURCE OF FUNDS
           BK; WC
 
    5.     CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
           PURSUANT TO ITEMS 2(e) OR 2(f)                                                / /
 
    6.     CITIZENSHIP OR PLACE OF ORGANIZATION
           The Netherlands
 
    7.     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH
           REPORTING PERSON
           536,960 shares of
           Common Stock pursuant to
           the five Stock Purchase Agreements
           dated as of June 10, 1998(1)
 
    8.     CHECK IF THE AGGREGATE AMOUNT IN ROW (7) EXCLUDES
           CERTAIN SHARES                                                                / /
 
    9.     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (7)
           15.3%
 
   10.     TYPE OF REPORTING PERSON
           CO
</TABLE>
 
(1) The Reporting Person disclaims beneficial ownership of such shares and this
    statement shall not be construed as an admission that the Reporting Person
    is the beneficial owner of any securities covered by this statement.
 
                                       5
<PAGE>
ITEM 1. SECURITY AND SUBJECT COMPANY.
 
    (a) The name of the subject company is Plenum Publishing Corporation, a
Delaware corporation (the "Company"), which has its principal executive offices
at 233 Spring Street, New York, New York, 10013.
 
    (b) The class of equity securities to which this statement relates is common
stock, par value $.10 per share. The information set forth in the Introduction
of the Offer to Purchase is incorporated herein by reference.
 
    (c) The information set forth in Section 6 ("Price Range of Shares;
Dividends") of the Offer to Purchase is incorporated herein by reference.
 
ITEM 2. IDENTITY AND BACKGROUND.
 
    (a)-(d) and (g) This Statement is filed by PPC Acquisition Corp., a Delaware
corporation (the "Offeror"), Kluwer Boston, Inc., a Massachusettes corporation
(the "Parent"), Wolters Kluwer U.S. Corporation, a Delaware Corporation
("WKUS"), and Wolters Kluwer nv, a corporation organized under the laws of the
Netherlands ("Wolters Kluwer"). The information set forth in the Introduction,
Section 9 ("Certain Information Concerning Wolters Kluwer, Wolters Kluwer
International, WKUS, WK America, the Parent and the Offeror") and Schedule I
("Directors and Executive Officers of Wolters Kluwer, Wolters Kluwer
International, WKUS, WK America, the Parent and the Offeror") of the Offer to
Purchase is incorporated herein by reference.
 
    (e) and (f) During the last five years, none of WKUS, Wolters Kluwer, Parent
or the Offeror and, to the best knowledge of the Parent and the Offeror, none of
the persons listed in Schedule I of the Offer to Purchase has been (i) convicted
in a criminal proceeding (excluding traffic violations or similar misdemeanors)
or (ii) a party to a civil proceeding of a judicial or administrative body of
competent jurisdiction and as a result of such proceeding was or is subject to a
judgment, decree or final order enjoining future violations of, or prohibiting
activities subject to, federal or state securities laws or finding any
violations of such laws.
 
ITEM 3. PAST CONTACTS, TRANSACTIONS OR NEGOTIATIONS WITH THE SUBJECT COMPANY
 
    (a) The information set forth in Section 9 ("Certain Information Concerning
Wolters Kluwer, Wolters Kluwer International, WKUS, WK America, the Parent and
the Offeror") and Section 11 ("Background of the Offer: Past Contacts,
Transactions or Negotiations with the Company") of the Offer to Purchase is
incorporated herein by reference.
 
    (b) The information set forth in the Introduction, Section 8 ("Certain
Information Concerning the Company"), Section 9 ("Certain Information Concerning
Wolters Kluwer, Wolters Kluwer International, WKUS, WK America, the Parent and
the Offeror"), Section 11 ("Background of the Offer; Past Contacts, Transactions
or Negotiations with the Company") and Section 12 ("Purpose of the Offer and the
Merger; Plans for the Company") of the Offer to Purchase is incorporated herein
by reference.
 
ITEM 4. SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION
 
    (a)-(b) The information set forth in Section 10 ("Source and Amount of
Funds") of the Offer to Purchase is incorporated herein by reference.
 
    (c) Not applicable.
 
                                       6
<PAGE>
ITEM 5. PURPOSE OF THE TENDER OFFER AND PLANS OR PROPOSALS OF THE BIDDER.
 
    (a)-(e) The information set forth in the Introduction, Section 11
("Background of the Offer; Past Contacts, Transactions or Negotiations with the
Company") and Section 12 ("Purpose of the Offer and the Merger; Plans for the
Company") of the Offer to Purchase is incorporated herein by reference.
 
    (f) and (g) The information set forth in Section 7 ("Certain Effects of the
Transaction") of the Offer to Purchase is incorporated herein by reference.
 
ITEM 6. INTEREST IN SECURITIES OF THE SUBJECT COMPANY.
 
    (a) and (b) The information set forth in the Introduction, Section 9
("Certain Information Concerning Wolters Kluwer, Wolters Kluwer International,
WKUS, WK America, the Parent and the Offeror"), Section 11 ("Background of the
Offer; Past Contacts, Transactions or Negotiations with the Company") and
Section 12 ("Purpose of the Offer and the Merger; Plans for the Company") of the
Offer to Purchase is incorporated herein by reference. As a result of the
Offeror's conditional option to purchase the Shares beneficially owned by the
stockholders who are party to the five Stock Purchase Agreements, each dated as
of June 10, 1998 with the Offeror, Wolters Kluwer, WKUS, the Parent and the
Offeror may be deemed to beneficially own an aggregate of 536,960 Shares
(representing approximately 15.3% of the Shares outstanding on June 10, 1998, on
a fully diluted basis.) However, each of Wolters Kluwer, WKUS, the Parent and
the Offeror have disclaimed beneficial ownership to such shares, and this
statement shall not be construed as an admission that any of Wolters Kluwer,
WKUS, the Parent or the Offerer are the beneficial owners of any securities
covered by this statement.
 
ITEM 7. CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH RESPECT TO
THE SUBJECT COMPANY'S SECURITIES.
 
    The information set forth in the Introduction, Section 9 ("Certain
Information Concerning Wolters Kluwer, Wolters Kluwer International, WKUS, WK
America, the Parent and the Offeror"), Section 11 ("Background of the Offer;
Past Contacts, Transactions or Negotiations with the Company") Section 12
("Purpose of the Offer; and the Merger Plans for the Company") and Section 13
("Merger Agreement, the Purchase Agreements, the Option Agreement and the WKUS
Letter") of the Offer to Purchase is incorporated herein by reference.
 
ITEM 8. PERSONS RETAINED, EMPLOYED OR TO BE COMPENSATED
 
    The information set forth in the Introduction and Section 16 ("Fees and
Expenses") of the Offer to Purchase is incorporated herein by reference.
 
ITEM 9. FINANCIAL STATEMENTS OF CERTAIN BIDDERS
 
    The information set forth in Section 9 ("Certain Information Concerning
Wolters Kluwer, Wolters Kluwer International, WKUS, WK America, the Parent and
the Offeror ") of the Offer to Purchase is incorporated herein by reference.
 
ITEM 10. ADDITIONAL INFORMATION.
 
    (a) The information set forth in the Introduction, Section 9 ("Certain
Information Concerning Wolters Kluwer, Wolters Kluwer International, WKUS, WK
America, the Parent and the Offeror"), Section 11 ("Background of the Offer,
Past Contacts, Transactions and Negotiations with the Company") and Section 12
("Purpose of the Offer and the Merger; Plans for the Company") of the Offer to
Purchase is incorporated herein by reference.
 
                                       7
<PAGE>
ITEM 10. ADDITIONAL INFORMATION. (CONTINUED)
    (b) and (c) The information set forth in the Introduction and Section 15
("Certain Legal Matters") of the Offer to Purchase is incorporated herein by
reference.
 
    (d) The information set forth in Section 7 ("Certain Effects of the
Transaction") of the Offer to Purchase is incorporated herein by reference.
 
    (e) Not applicable.
 
    (f) The information set forth in the Offer to Purchase and the Letter of
Transmittal, copies of which are attached hereto as exhibits (a)(1) and (a)(2),
respectively, is incorporated herein by reference.
 
ITEM 11. MATERIAL TO BE FILED AS EXHIBITS.
 
<TABLE>
<S>        <C>
(a)(1)     Form of Offer to Purchase dated June 10, 1998.
(a)(2)     Form of Letter of Transmittal.
(a)(3)     Form of Notice of Guaranteed Delivery.
(a)(4)     Form of Letter from Credit Suisse First Boston Corporation to Brokers, Dealers,
           Commercial Banks, Trust Companies and Other Nominees.
(a)(5)     Form of Letter from Brokers, Dealers, Commercial Banks, Trust Companies and Other
           Nominees to Clients.
(a)(6)     Form of Letter from the Parent to participants of the Company's Profit Sharing
           Plan.
(a)(7)     Form of Guidelines for Certification of Taxpayer Identification Number on
           Substitute Form W-9.
(a)(8)     Summary Advertisement to be published in The Wall Street Journal on June 16, 1998.
(a)(9)     Joint Press Release issued by the Company and Wolters Kluwer on June 10, 1998
(b)        Not applicable.
(c)(1)     Agreement and Plan of Merger, dated as of June 10, 1998, among the Parent, the
           Offeror and the Company.
(c)(2)     Stock Purchase Agreement, dated as of June 10, 1998, between the Offeror and
           Martin Tash and Arlene Tash, together with a Guaranty of Parent.
(c)(3)     Stock Purchase Agreement, dated as of June 10, 1998, between the Offeror and Mark
           Shaw and Hally Shaw, together with a Guaranty of Parent.
(c)(4)     Stock Purchase Agreement, dated as of June 10, 1998, between the Offeror and
           Ghanshyam Patel and Anila Patel, together with a Guaranty of Parent.
(c)(5)     Stock Purchase Agreement, dated as of June 10, 1998, between the Offeror and
           Bernard Bressler, together with a Guaranty of Parent.
(c)(6)     Stock Purchase Agreement, dated as of June 10, 1998, between the Offeror and
           Teresa Bressler, together with a Guaranty of Parent.
(c)(7)     Stock Option Agreement, dated June 10, 1998 between the Parent and the Company.
(c)(8)     Letter, dated June 10, 1998, from WKUS to the Company.
(c)(9)     Confidentiality Agreement, dated as of April 6, 1998, between WKUS and Salomon
           Smith Barney.
(c)(10)    Exclusivity Agreement, dated as of June 4, 1998, between WKUS and the Company.
(d)        Not applicable.
(e)        Not applicable.
(f)        None.
</TABLE>
 
                                       8
<PAGE>
                                   SIGNATURE
 
    After due inquiry and to the best of my knowledge and belief, I certify that
the information set forth in this statement is true, complete and correct.
 
<TABLE>
<S>                                          <C>        <C>
Dated: June 16, 1998                         PPC Acquisition Corp.
 
                                             By:        /s/ JEFFREY K. SMITH
                                                        ------------------------------------------
                                                        Name: Jeffrey K. Smith
                                                        Title: President
</TABLE>
 
<PAGE>
                                   SIGNATURE
 
    After due inquiry and to the best of my knowledge and belief, I certify that
the information set forth in this statement is true, complete and correct.
 
<TABLE>
<S>                                          <C>        <C>
Dated: June 16, 1998                         Kluwer Boston, Inc.
 
                                             By:        /s/ JEFFREY K. SMITH
                                                        ------------------------------------------
                                                        Name: Jeffrey K. Smith
                                                        Title: President
</TABLE>
 
<PAGE>
                                   SIGNATURE
 
    After due inquiry and to the best of my knowledge and belief, I certify that
the information set forth in this statement is true, complete and correct.
 
<TABLE>
<S>                                          <C>        <C>
Dated: June 16, 1998                         Wolters Kluwer U.S. Corporation
 
                                             By:        /s/ PETER W. VAN WEL
                                                        ------------------------------------------
                                                        Name: Peter W. van Wel
                                                        Title: President and CEO
</TABLE>
 
<PAGE>
                                   SIGNATURE
 
    After due inquiry and to the best of my knowledge and belief, I certify that
the information set forth in this statement is true, complete and correct.
 
<TABLE>
<S>                                          <C>        <C>
Dated: June 16, 1998                         Wolters Kluwer nv
 
                                             By:        /s/ PETER W. VAN WEL
                                                        ------------------------------------------
                                                        Name: Peter W. van Wel
                                                        Title: Member, Executive Board
</TABLE>
<PAGE>
                                 EXHIBIT INDEX
 
<TABLE>
<CAPTION>
EXHIBIT
NO.                                                      DESCRIPTION
- ---------  --------------------------------------------------------------------------------------------------------
 
<S>        <C>
(a)(1)     Form of Offer to Purchase dated June 10, 1998.
 
(a)(2)     Form of Letter of Transmittal.
 
(a)(3)     Form of Notice of Guaranteed Delivery.
 
(a)(4)     Form of Letter from Credit Suisse First Boston Corporation to Brokers, Dealers, Commercial Banks, Trust
           Companies and Other Nominees.
 
(a)(5)     Form of Letter from Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees to Clients.
 
(a)(6)     Form of Letter from the Parent to participants in the Company's Profit Sharing Plan.
 
(a)(7)     Form of Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9.
 
(a)(8)     Summary Advertisement to be published in The Wall Street Journal on June 16, 1998.
 
(a)(9)     Joint Press Release issued by the Company and Wolters Kluwer on June 10, 1998.
 
(b)        Not applicable.
 
(c)(1)     Agreement and Plan of Merger, dated as of June 10, 1998, among the Parent, the Offeror and the Company.
 
(c)(2)     Stock Purchase Agreement, dated as of June 10, 1998, between the Offeror and Martin Tash and Arlene
           Tash, together with a Guaranty of Parent.
 
(c)(3)     Stock Purchase Agreement, dated as of June 10, 1998, between the Offeror and Mark Shaw and Hally Shaw,
           together with a Guaranty of Parent.
 
(c)(4)     Stock Purchase Agreement, dated as of June 10, 1998, between the Offeror and Ghanshyam Patel and Anila
           Patel, together with a Guaranty of Parent.
 
(c)(5)     Stock Purchase Agreement, dated as of June 10, 1998, between the Offeror and Bernard Bressler, together
           with a Guaranty of Parent.
 
(c)(6)     Stock Purchase Agreement, dated as of June 10, 1998, between the Offeror and Teresa Bressler, together
           with a Guaranty of Parent.
 
(c)(7)     Stock Option Agreement, dated June 10, 1998 between the Parent and the Company.
 
(c)(8)     Letter, dated June 10, 1998, from WKUS to the Company.
 
(c)(9)     Confidentiality Agreement, dated as of April 6, 1998, between WKUS and Salomon Smith Barney.
 
(c)(10)    Exclusivity Agreement, dated as of June 4, 1998 between WKUS and the Company.
 
(d)        Not applicable.
 
(e)        Not applicable.
 
(f)        None.
</TABLE>

<PAGE>
                           Offer to Purchase for Cash
 
                     All Outstanding Shares of Common Stock
 
                                       of
 
                         Plenum Publishing Corporation
 
                                       at
 
                              $73.50 Net Per Share
 
                                       by
 
                             PPC Acquisition Corp.
 
                      a direct wholly owned subsidiary of
 
                              Kluwer Boston, Inc.
 
     THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK
                                      CITY
        TIME, ON WEDNESDAY, JULY 15, 1998, UNLESS THE OFFER IS EXTENDED.
 
THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS, (i) THERE BEING VALIDLY
TENDERED BY THE EXPIRATION DATE AND NOT WITHDRAWN THAT NUMBER OF SHARES OF
 COMMON STOCK, PAR VALUE $.10 PER SHARE ("SHARES"), OF PLENUM PUBLISHING
   CORPORATION (THE "COMPANY") WHICH, TOGETHER WITH THE SHARES TO BE
    ACQUIRED PURSUANT TO THE PURCHASE AGREEMENTS SIMULTANEOUSLY WITH THE
     ACCEPTANCE OF SHARES PURSUANT TO THE OFFER, REPRESENT AT LEAST THAT
       NUMBER OF SHARES WHICH WOULD CONSTITUTE A MAJORITY OF THE SHARES
       OUTSTANDING ON A FULLY DILUTED BASIS, (ii) RECEIPT BY THE
         OFFEROR OF CERTAIN GOVERNMENTAL APPROVALS AND (iii) THE
          SATISFACTION OF CERTAIN OTHER TERMS AND CONDITIONS. SEE
          SECTION 14--"CERTAIN CONDITIONS TO THE OFFEROR'S
            OBLIGATIONS", WHICH        SETS FORTH IN FULL THE
                            CONDITIONS OF THE OFFER.
 
THE OFFER IS BEING MADE IN CONNECTION WITH THE AGREEMENT AND PLAN OF MERGER,
DATED AS OF JUNE 10, 1998, BY AND AMONG KLUWER BOSTON, INC., PPC ACQUISITION
   CORP. AND THE COMPANY. THE BOARD OF DIRECTORS OF THE COMPANY HAS
     UNANIMOUSLY APPROVED THE OFFER, THE MERGER AND THE MERGER AGREEMENT,
       HAS UNANIMOUSLY DETERMINED THAT THE OFFER AND THE MERGER ARE
          FAIR TO, AND IN THE BEST INTERESTS OF, THE COMPANY'S
              STOCKHOLDERS AND RECOMMENDS THAT THE COMPANY'S
                STOCKHOLDERS ACCEPT THE OFFER AND TENDER
                   THEIR SHARES PURSUANT TO
                                            THE OFFER.
 
                                   IMPORTANT
 
    Any stockholder desiring to tender Shares should either (i) complete and
sign the Letter of Transmittal or a facsimile thereof in accordance with the
instructions in the Letter of Transmittal and deliver the Letter of Transmittal
with the Shares and all other required documents to the Depositary, or follow
the procedure for book-entry transfer set forth in Section 3-- "Procedure for
Tendering Shares" or (ii) request such stockholder's broker, dealer, commercial
bank, trust company or other nominee to effect the transaction for the
stockholder. Stockholders having Shares registered in the name of a broker,
dealer, commercial bank, trust company or other nominee must contact such person
if they desire to tender their Shares.
 
    Any stockholder who desires to tender Shares and whose certificates
representing such Shares are not immediately available, or who cannot comply
with the procedures for book-entry transfer on a timely basis, may tender such
Shares pursuant to the guaranteed delivery procedure set forth in Section
3--"Procedure for Tendering Shares".
 
    Questions and requests for assistance or additional copies of this Offer to
Purchase, Letter of Transmittal or any other tender offer materials may be
directed to the Information Agent or the Dealer Manager at their respective
addresses and telephone numbers set forth on the back cover of this Offer to
Purchase.
 
                      The Dealer Manager for the Offer is:
 
                                     [LOGO]
 
June 16, 1998
<PAGE>
                               TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                                                                                                                PAGE
                                                                                                                -----
<S>                                                                                                          <C>
 
INTRODUCTION...............................................................................................           1
 
   1. Terms of the Offer...................................................................................           3
   2. Acceptance for Payment and Payment for Shares........................................................           4
   3. Procedure for Tendering Shares.......................................................................           5
   4. Withdrawal Rights....................................................................................           8
   5. Certain United States Federal Income Tax Considerations..............................................           9
   6. Price Range of Shares; Dividends.....................................................................          10
   7. Certain Effects of the Transaction...................................................................          10
   8. Certain Information Concerning the Company...........................................................          11
   9. Certain Information Concerning Wolters Kluwer, Wolters Kluwer International, WKUS, WK America, the
      Parent and the Offeror...............................................................................          13
  10. Source and Amount of Funds...........................................................................          15
  11. Background of the Offer; Past Contacts, Transactions or Negotiations with the Company................          16
  12. Purpose of the Offer and the Merger; Plans for the Company...........................................          17
  13. The Merger Agreement, the Purchase Agreements, the Option Agreement and the
       WKUS Letter.........................................................................................          18
  14. Certain Conditions to the Offeror's Obligations......................................................          29
  15. Certain Legal Matters................................................................................          30
  16. Fees and Expenses....................................................................................          32
  17. Miscellaneous........................................................................................          33
 
     Schedule I -- Directors and Executive Officers of Wolters Kluwer, Wolters Kluwer International, WKUS,
      WK America, the Parent and the Offeror...............................................................         I-1
</TABLE>
 
                                       i
<PAGE>
To the Holders of Common Stock,
par value $.10 per share, of Plenum Publishing Corporation:
 
                                  INTRODUCTION
 
    PPC Acquisition Corp., a Delaware corporation (the "Offeror") and a direct
wholly owned subsidiary of Kluwer Boston, Inc., a Massachusetts corporation (the
"Parent"), hereby offers to purchase all outstanding shares of Common Stock, par
value $.10 per share (the "Common Stock" or the "Shares"), of Plenum Publishing
Corporation, a Delaware corporation (the "Company"), at a purchase price of
$73.50 per Share net to the seller in cash (such price, or such higher price per
Share as may be paid in the Offer (as defined below), referred to herein as the
"Offer Price"), without interest thereon, upon the terms and subject to the
conditions set forth in this Offer to Purchase and in the related Letter of
Transmittal (which, together with any amendments or supplements thereto,
constitute the "Offer"). Tendering holders of record of Shares who tender
directly will not be obligated to pay brokerage fees or commissions or, except
as set forth in the Letter of Transmittal, transfer taxes on the purchase of
Shares by the Offeror pursuant to the Offer. Stockholders who hold their Shares
through a bank or broker should check with such institution as to whether they
charge any service fees. The Offeror will pay all charges and expenses of Credit
Suisse First Boston Corporation, which is acting as Dealer Manager for the Offer
(in such capacity, the "Dealer Manager"), Morgan Guaranty Trust Company of New
York (the "Depositary") and Georgeson & Company Inc. (the "Information Agent")
in connection with the Offer. See Section 16--"Fees and Expenses".
 
    THE BOARD OF DIRECTORS OF THE COMPANY HAS UNANIMOUSLY APPROVED THE OFFER,
THE MERGER (AS HEREINAFTER DEFINED) AND THE MERGER AGREEMENT (AS HEREINAFTER
DEFINED), HAS UNANIMOUSLY DETERMINED THAT THE OFFER AND THE MERGER ARE FAIR TO,
AND IN THE BEST INTERESTS OF, THE COMPANY'S STOCKHOLDERS, AND RECOMMENDS THAT
THE COMPANY'S STOCKHOLDERS ACCEPT THE OFFER AND TENDER THEIR SHARES IN THE
OFFER.
 
    THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS, THERE BEING VALIDLY
TENDERED BY THE EXPIRATION DATE (AS DEFINED BELOW) AND NOT WITHDRAWN THAT NUMBER
OF SHARES WHICH, TOGETHER WITH THE SHARES TO BE ACQUIRED PURSUANT TO THE
PURCHASE AGREEMENTS (AS DEFINED BELOW) SIMULTANEOUSLY WITH THE ACCEPTANCE OF
SHARES PURSUANT TO THE OFFER, REPRESENT AT LEAST THAT NUMBER OF SHARES WHICH
WOULD CONSTITUTE A MAJORITY OF THE SHARES OUTSTANDING ON A FULLY DILUTED BASIS
(THE "MINIMUM CONDITION"). THE OFFER IS ALSO CONDITIONED UPON RECEIPT BY THE
OFFEROR OF CERTAIN GOVERNMENTAL APPROVALS AND THE SATISFACTION OF OTHER TERMS
AND CONDITIONS. SEE SECTION 14--"CERTAIN CONDITIONS TO THE OFFEROR'S
OBLIGATIONS".
 
    Salomon Smith Barney, the Company's financial advisor, has delivered to the
Company's Board of Directors its written opinion that the consideration to be
received by the stockholders of the Company pursuant to the Offer and the Merger
is fair to such stockholders from a financial point of view. A copy of such
opinion is contained in the Company's Statement on Schedule 14D-9 which is being
distributed to the Company's stockholders.
 
    The Offer is being made pursuant to the Agreement and Plan of Merger, dated
as of June 10, 1998 (the "Merger Agreement"), by and among the Parent, the
Offeror and the Company. The Merger Agreement provides that, among other things,
as soon as practicable after the purchase of Shares pursuant to the Offer and
the satisfaction of the other conditions set forth in the Merger Agreement and
in accordance with the relevant provisions of the Delaware General Corporation
Law, as amended (the "Delaware GCL"), the Offeror will be merged with and into
the Company (the "Merger"). See Section 12--"Purpose of the Offer and the
Merger; Plans for the Company". Following consummation of the Merger, the
Company will continue as the surviving corporation (the "Surviving Corporation")
and will be a direct wholly owned subsidiary of the Parent. At the effective
time of the Merger (the "Effective Time"), each share of the Common Stock that
is issued and outstanding (other than shares held by the Parent, the Offeror,
any wholly owned subsidiary of the Parent or the Offeror, or in the treasury of
the Company,
 
                                       1
<PAGE>
which shall be cancelled, and shares held by stockholders who have properly
exercised appraisal rights under Delaware law, if any), will be converted into
the right to receive the Offer Price, without interest thereon, upon surrender
of the certificates formerly representing such Shares. See Section 5--"Certain
United States Federal Income Tax Considerations" for a description of certain
tax consequences of the Offer and the Merger. Wolters Kluwer U.S. Corporation, a
Delaware corporation ("WKUS"), has agreed to fund the obligations of the Parent
and the Offeror through available cash balances and existing bank credit lines
of Wolters Kluwer nv, a corporation organized under the laws of the Netherlands
("Wolters Kluwer"), pursuant to a letter, dated June 10, 1998, from WKUS to the
Company (the "WKUS Letter"). See Section 13--"The Merger Agreement, the Purchase
Agreements, the Option Agreement and the WKUS Letter".
 
    The Merger Agreement provides that, promptly after the Offeror acquires
Shares pursuant to the Offer, the Parent will be entitled to designate up to
that number of directors of the Board of Directors of the Company (rounded up to
the next whole number) as will make the percentage of the Company's directors
designated by the Parent equal to the aggregate voting power of the Shares held
by the Parent and any of its subsidiaries.
 
    The Offeror has entered into five Stock Purchase Agreements, each dated as
of June 10, 1998 (the "Purchase Agreements"), with the stockholders identified
therein (each a "Stockholder" and collectively, the "Stockholders") beneficially
owning an aggregate of 536,960 Shares representing approximately 15.3% of the
outstanding Shares on a fully diluted basis (the "Stockholders' Shares")
pursuant to which the Stockholders have, among other things, (i) agreed to
tender into the Offer all of the Stockholders' Shares and not withdraw any of
the Stockholders' Shares unless an election is made by the Offeror to purchase
the Stockholders' Shares and (ii) granted to the Offeror an option to purchase
the Stockholders' Shares exercisable in certain limited circumstances following
the Expiration Date or the termination of the Offer by the Offeror. In addition,
each Stockholder has agreed to appoint the Offeror under certain circumstances
as such Stockholder's proxy to vote such Stockholder's Shares on all matters in
connection with the consummation of the transactions contemplated by the Merger
Agreement and the Purchase Agreements. The tender by the Stockholders of the
Stockholders' Shares alone will not itself cause the Minimum Condition to be
satisfied.
 
    The Company has advised the Offeror that as of June 10, 1998, there were
3,510,251 Shares issued and outstanding. The Company has further advised the
Offeror that (i) as of June 10, 1998, the Company has no shares of capital stock
reserved for future issuance and the Company has no outstanding options to
purchase any shares of capital stock and (ii) since March 31, 1998, the Company
has not issued any shares of capital stock. As of the date hereof, neither the
Offeror nor the Parent beneficially owns any Shares. If the Offeror acquires at
least 1,755,126 Shares in the Offer (including the 536,960 Shares subject to the
Purchase Agreements), the Minimum Condition will be satisfied. Accordingly, the
Offeror would have sufficient voting power to approve the Merger without the
affirmative vote of any other stockholder. In the event that the Offeror
acquires 90% or more of the Shares, the Parent would be able to effectuate the
Merger by appropriate resolutions of the Boards of Directors of the Offeror and
the Company without any meeting or action by the stockholders of the Company.
 
    The Offeror has been advised by the Company that, to the best of the
Company's knowledge, all of the Company's directors and executive officers
currently intend to tender all Shares owned by them pursuant to the Offer.
 
    THIS OFFER TO PURCHASE AND THE RELATED LETTER OF TRANSMITTAL CONTAIN
IMPORTANT INFORMATION WHICH SHOULD BE READ BEFORE ANY DECISION IS MADE WITH
RESPECT TO THE OFFER.
 
                                       2
<PAGE>
1. TERMS OF THE OFFER.
 
    Upon the terms and subject to the conditions of the Offer (including, if the
Offer is extended or amended, the terms and conditions of any extension or
amendment), the Offeror will accept for payment and pay for all Shares validly
tendered prior to the Expiration Date and not theretofore withdrawn in
accordance with Section 4--"Withdrawal Rights". The term "Expiration Date" means
12:00 Midnight, New York City time, on Wednesday, July 15, 1998, unless and
until the Offeror shall have extended the period of time for which the Offer is
open, in which event the term "Expiration Date" shall mean the latest time and
date at which the Offer, as so extended by the Offeror, shall expire.
 
    If the Offeror shall decide, in its sole discretion, to increase the
consideration offered in the Offer to holders of Shares and if, at the time that
notice of such increase is first published, sent or given to holders of Shares
in the manner specified below, the Offer is scheduled to expire at any time
earlier than the expiration of a period ending on the tenth business day from,
and including, the date that such notice is first so published, sent or given,
then the Offer will be extended until the expiration of such period of ten
business days. For purposes of the Offer, a "business day" means any day other
than a Saturday, Sunday or a federal holiday, and consists of the time period
from 12:01 a.m. through 12:00 Midnight, New York City time.
 
    THE OFFER IS CONDITIONED UPON SATISFACTION OF THE MINIMUM CONDITION AND THE
OFFEROR OBTAINING CERTAIN GOVERNMENTAL APPROVALS. THE MERGER AGREEMENT AND THE
OFFER MAY BE TERMINATED BY THE OFFEROR AND THE PARENT IF CERTAIN EVENTS OCCUR.
THE OFFER IS ALSO SUBJECT TO OTHER TERMS AND CONDITIONS. SEE SECTION
14--"CERTAIN CONDITIONS TO THE OFFEROR'S OBLIGATIONS". The Offeror expressly
reserves the right (but shall not be obligated), in accordance with applicable
rules and regulations of the United States Securities and Exchange Commission
(the "Commission"), and subject to the limitations set forth in the Merger
Agreement and described below, to waive any condition (other than the Minimum
Condition) to the Offer prior to the Expiration Date. If the Minimum Condition
or any of the other conditions set forth in Section 14--"Certain Conditions to
the Offeror's Obligations" have not been satisfied, by 12:00 Midnight, New York
City time, then on Wednesday, July 15, 1998 (or any other time then set as the
Expiration Date), the Offeror may, subject to the terms of the Merger Agreement
as described below, elect to (i) extend the Offer and, subject to applicable
withdrawal rights, retain all tendered Shares until the expiration of the Offer,
as extended, (ii) subject to complying with applicable rules and regulations of
the Commission, accept for payment all Shares so tendered and not extend the
Offer, or (iii) terminate the Offer and not accept for payment any Shares and
return all tendered Shares to tendering stockholders.
 
    Pursuant to the Merger Agreement, neither the Parent nor the Offeror may
decrease the price per Share or change the form of consideration payable in the
Offer, decrease the number of Shares sought to be purchased in the Offer, change
the conditions set forth in Section 14--"Certain Conditions to the Offeror's
Obligations" to the Merger Agreement, impose additional conditions to the Offer
or amend any other term of the Offer in any manner materially adverse to the
holders of the Shares. Subject to the terms of the Offer and the Merger
Agreement and the satisfaction or waiver of all the conditions of the Offer set
forth Section 14--"Certain Conditions to the Offeror's Obligations" to the
Merger Agreement as of the Expiration Date, the Parent and/or the Offeror will
accept for payment and pay for all Shares validly tendered and not properly
withdrawn pursuant to the Offer as soon as practicable after the Expiration
Date. Notwithstanding the foregoing, the Offeror may, without the consent of the
Company, (i) extend the Offer on one or more occasions for up to ten business
days for each such extension beyond the Expiration Date, if at the then
scheduled expiration date of the Offer any of the conditions to the Offeror's
obligation to accept for payment and pay for the Shares shall not be satisfied
or waived, until such time as such conditions are satisfied or waived, (ii)
increase the Offer Price and extend the Offer for any period required by any
rule, regulation, interpretation or provision of the Commission or the staff
thereof applicable to the Offer and (iii) extend the Offer for an aggregate
period of not more than 10 business days beyond the latest expiration date that
would otherwise be permitted under clause (i) or (ii) of this sentence
 
                                       3
<PAGE>
if there shall not have been tendered and not withdrawn pursuant to the Offer at
least 90% of the outstanding Shares.
 
    The Offeror also expressly reserves the right, at any time and from time to
time subject to the terms of the Merger Agreement and regardless of whether any
of the events set forth in Section 14--"Certain Conditions to the Offeror's
Obligations" shall have occured or shall have been determined by the Offeror to
have occured, (i) to extend the period of time during which the Offer is open
and thereby delay acceptance for payment of, and the payment for, any Shares
regardless of whether such Shares were theretofore accepted for payment, or to
terminate the Offer and not to accept for payment or pay for any Shares not
theretofore accepted for payment or paid for, upon the occurrence of any of the
conditions set forth in Section 14--"Certain Conditions to the Offeror's
Obligations," by giving written notice of such extension or termination to the
Depositary, and (ii) at any time or from time to time, to amend the Offer in any
respect. The Offeror's right to delay payment for any Shares or not to pay for
any Shares theretofore accepted for payment is subject to the applicable rules
and regulations of the Commission, including Rule l4e-l(c) under the Securities
Exchange Act of 1934, as amended (the "Exchange Act"), relating to the Offeror's
obligation to pay for or return tendered Shares promptly after the termination
or withdrawal of the Offer. Under no circumstances will interest be paid on the
purchase price for tendered Shares, whether or not the Offeror exercises its
right to extend the Offer. There can be no assurance that the Offeror will
exercise its rights to extend the Offer.
 
    Any extension of the period during which the Offer is open, delay in
acceptance for payment or termination or amendment of the Offer will be
followed, as promptly as practicable, by public announcement thereof, such
announcement in the case of an extension to be issued not later than 9:00 a.m.,
New York City time, on the next business day after the previously scheduled
Expiration Date in accordance with the public announcement requirements of Rules
14d-4(c) and 14e-l(d) under the Exchange Act. Without limiting the obligation of
the Offeror under such rule or the manner in which the Offeror may choose to
make any public announcement, the Offeror currently intends to make
announcements by issuing a press release to the Dow Jones News Service and
making any appropriate filing with the Commission.
 
    If, subject to the terms of the Merger Agreement, the Offeror makes a
material change in the terms of the Offer or the information concerning the
Offer, or if it waives a material condition of the Offer, the Offeror will
disseminate additional tender offer materials and extend the Offer if and to the
extent required by Rules 14d-4(c), 14d-6(d) and 14e-1 under the Exchange Act or
otherwise. The minimum period during which a tender offer must remain open
following material changes in the terms of the offer or the information
concerning the offer, other than a change in price or a change in percentage of
securities sought, will depend upon the facts and circumstances, including the
relative materiality of the terms or information changes. With respect to a
change in price or a change in percentage of securities sought, a minimum ten
business day period is generally required to allow for adequate dissemination to
stockholders and investor response.
 
    The Company has provided the Offeror its list of stockholders and security
position listings for the purpose of disseminating the Offer to holders of
Shares. This Offer to Purchase, Letter of Transmittal and other related
materials will be mailed to record holders of Shares whose names appear on the
Company's stockholder list and will be furnished to brokers, dealers, commercial
banks, trust companies and similar persons whose names, or the names of whose
nominees, appear on the stockholder list or, if applicable, who are listed as
participants in a clearing agency's security position listing for subsequent
transmittal to beneficial owners of Shares.
 
2. ACCEPTANCE FOR PAYMENT AND PAYMENT FOR SHARES.
 
    Upon the terms and subject to the conditions of the Offer (including, if the
Offer is extended or amended, the terms and conditions of any such extension or
amendment), the Offeror will accept for payment and will pay for all Shares
validly tendered prior to the Expiration Date and not theretofore withdrawn in
accordance with Section 4--"Withdrawal Rights" promptly after the later to occur
of (a) the
 
                                       4
<PAGE>
Expiration Date and (b) subject to compliance with Rule 14e-l(c) under the
Exchange Act, the satisfaction or waiver of the conditions set forth in Section
14--"Certain Conditions to the Offeror's Obligations". WKUS has agreed to fund
the obligations of the Parent and the Offeror under the Merger Agreement in
accordance with the terms of the WKUS Letter. See Section 13--"The Merger
Agreement, the Purchase Agreements, the Option Agreement and the WKUS Letter".
Subject to compliance with Rule 14e-l(c) under the Exchange Act, the Offeror
expressly reserves the right to delay payment for Shares in order to comply in
whole or in part with any applicable law. See Section 1--"Terms of the Offer"
and Section 15--"Certain Legal Matters". In all cases, payment for Shares
tendered and accepted for payment pursuant to the Offer will be made only after
timely receipt by the Depositary of (i) certificates for such Shares or timely
confirmation (a "Book-Entry Confirmation") of a book-entry transfer of such
Shares into the Depositary's account at The Depository Trust Company (the
"Book-Entry Transfer Facility"), pursuant to the procedures set forth in Section
3--"Procedures for Tendering Shares", (ii) a properly completed and duly
executed Letter of Transmittal (or a manually signed facsimile thereof) with all
required signature guarantees or in the case of a book-entry transfer, an
Agent's Message (as defined below), and (iii) any other documents required by
the Letter of Transmittal.
 
    The term "Agent's Message" means a message transmitted by the Book-Entry
Transfer Facility to, and received by, the Depositary and forming a part of a
Book-Entry Confirmation, which states that the Book-Entry Transfer Facility has
received an express acknowledgment from the participant in the Book-Entry
Transfer Facility tendering the Shares that such participant has received and
agrees to be bound by the terms of the Letter of Transmittal and that the
Offeror may enforce such agreement against the participant.
 
    For purposes of the Offer, the Offeror will be deemed to have accepted for
payment, and thereby purchased, Shares validly tendered and not withdrawn as, if
and when the Offeror gives written notice to the Depositary of the Offeror's
acceptance of such Shares for payment. In all cases, payment for Shares
purchased pursuant to the Offer will be made by deposit of the purchase price
with the Depositary, which will act as agent for tendering stockholders for the
purpose of receiving payment from the Offeror and transmitting such payment to
tendering stockholders. If, for any reason whatsoever, acceptance for payment of
any Shares tendered pursuant to the Offer is delayed, or the Offeror is unable
to accept for payment Shares tendered pursuant to the Offer, then, without
prejudice to the Offeror's rights under Section 1--"Terms of the Offer", the
Depositary may, nevertheless, on behalf of the Offeror, retain tendered Shares,
and such Shares may not be withdrawn, except to the extent that the tendering
stockholders are entitled to withdrawal rights as described in Section
4--"Withdrawal Rights" below and as otherwise required by Rule 14e-l(c) under
the Exchange Act. Under no circumstances will interest be paid by the Offeror
because of any delay in making such payment.
 
    If any tendered Shares are not accepted for payment pursuant to the terms
and conditions of the Offer for any reason, or if certificates are submitted for
more Shares than are tendered, certificates for such unpurchased or untendered
Shares will be returned, without expense to the tendering stockholder (or, in
the case of Shares delivered by book-entry transfer to the Book-Entry Transfer
Facility, such Shares will be credited to an account maintained within the
Book-Entry Transfer Facility), as promptly as practicable after the expiration,
termination or withdrawal of the Offer.
 
    If, prior to the Expiration Date, the Offeror increases the price being paid
for Shares accepted for payment pursuant to the Offer, such increased
consideration will be paid to all stockholders whose Shares are purchased
pursuant to the Offer, whether or not such Shares were tendered prior to such
increase in consideration.
 
3. PROCEDURE FOR TENDERING SHARES.
 
    VALID TENDERS.  For Shares to be validly tendered pursuant to the Offer, a
properly completed and duly executed Letter of Transmittal (or a manually signed
facsimile thereof), with any required signature guarantees, or, in the case of a
book-entry transfer, an Agent's Message, and any other required
 
                                       5
<PAGE>
documents, must be received by the Depositary at the address set forth on the
back cover of this Offer to Purchase prior to the Expiration Date, or the
tendering stockholder must comply with the guaranteed delivery procedure set
forth below. In addition, either (i) certificates representing such Shares must
be received by the Depositary along with the Letter of Transmittal or such
Shares must be tendered pursuant to the procedure for book-entry transfer set
forth below, and a Book-Entry Confirmation must be received by the Depositary,
in each case prior to the Expiration Date, or (ii) the guaranteed delivery
procedures set forth below must be complied with. No alternative, conditional or
contingent tenders will be accepted. Delivery of documents to the Book-Entry
Transfer Facility in accordance with the Book-Entry Transfer Facility's
procedures does not constitute delivery to the Depositary.
 
    BOOK-ENTRY TRANSFER.  The Depositary will make a request to establish an
account with respect to the Shares at the Book-Entry Transfer Facility for
purposes of the Offer within two business days after the date of this Offer to
Purchase. Any financial institution that is a participant in the Book-Entry
Transfer Facility's system may make book-entry delivery of Shares by causing the
Book-Entry Transfer Facility to transfer such Shares into the Depositary's
account at the Book-Entry Transfer Facility in accordance with the Book-Entry
Transfer Facility procedures for transfer. Although delivery of Shares may be
effected through book-entry at the Book-Entry Transfer Facility prior to the
Expiration Date, (i) the Letter of Transmittal (or a manually signed facsimile
thereof), properly completed and duly executed, with any required signature
guarantees, or an Agent's Message in connection with a book-entry transfer and
any other required documents, must, in any case, be transmitted to and received
by the Depositary at the address set forth on the back cover of this Offer to
Purchase or (ii) the guaranteed delivery procedures described below must be
complied with.
 
    SIGNATURE GUARANTEE.  Signatures on the Letter of Transmittal must be
guaranteed by a member in good standing of the Securities Transfer Agents
Medallion Program, or by any other bank, broker, dealer, credit union, savings
association or other entity which is an "eligible guarantor institution," as
such term is defined in Rule l7Ad-15 under the Exchange Act (each of the
foregoing being referred to as an "Eligible Institution" and collectively, as
"Eligible Institutions"), unless the Shares tendered thereby are tendered (i) by
a registered holder of Shares who has not completed either the box labeled
"Special Delivery Instructions" or the box labeled "Special Payment
Instructions" on the Letter of Transmittal or (ii) for the account of any
Eligible Institution. If the certificates evidencing Shares are registered in
the name of a person or persons other than the signer of the Letter of
Transmittal, or if payment is to be made, or delivered to, or certificates for
unpurchased Shares are to be issued or returned to, a person other than the
registered owner or owners, then the tendered certificates must be endorsed or
accompanied by duly executed stock powers, in either case signed exactly as the
name or names of the registered owner or owners appear on the certificates, with
the signatures on the certificates or stock powers guaranteed by an Eligible
Institution as provided in the Letter of Transmittal. See Instructions 1 and 5
to the Letter of Transmittal.
 
    GUARANTEED DELIVERY.  If a stockholder desires to tender Shares pursuant to
the Offer and such stockholder's certificates for Shares are not immediately
available or time will not permit all required documents to reach the Depositary
prior to the Expiration Date or the procedure for book-entry transfer cannot be
completed on a timely basis, such Shares may nevertheless be tendered if all of
the following guaranteed delivery procedures are duly complied with:
 
        (i) the tender is made by or through an Eligible Institution;
 
        (ii) a properly completed and duly executed Notice of Guaranteed
    Delivery, substantially in the form made available by the Offeror, is
    received by the Depositary, as provided below, prior to the Expiration Date;
    and
 
       (iii) the certificates for all tendered Shares, in proper form for
    transfer (or a Book-Entry Confirmation), together with a properly completed
    and duly executed Letter of Transmittal (or a manually signed facsimile
    thereof), and any required signature guarantees, or, in the case of a book-
 
                                       6
<PAGE>
    entry transfer, an Agent's Message, and any other documents required by the
    Letter of Transmittal, are received by the Depositary within three trading
    days after the date of such Notice of Guaranteed Delivery. The term "trading
    day" is any day on which the NASDAQ National Market is open for business.
 
    The Notice of Guaranteed Delivery may be delivered by hand or transmitted by
facsimile transmission or mail to the Depositary and must include a guarantee by
an Eligible Institution in the form set forth in the Notice of Guaranteed
Delivery.
 
    THE METHOD OF DELIVERY OF SHARES, THE LETTER OF TRANSMITTAL AND ALL OTHER
REQUIRED DOCUMENTS, INCLUDING DELIVERY THROUGH THE BOOK-ENTRY TRANSFER FACILITY,
IS AT THE OPTION AND RISK OF THE TENDERING STOCKHOLDER. IF DELIVERY IS BY MAIL,
REGISTERED MAIL WITH RETURN RECEIPT REQUESTED, PROPERLY INSURED, IS RECOMMENDED.
 
    Notwithstanding any other provision hereof, payment for Shares accepted for
payment pursuant to the Offer will in all cases be made only after timely
receipt by the Depositary of (i) certificates for such Shares or the Book-Entry
Confirmation, (ii) a properly completed and duly executed Letter of Transmittal
(or a manually signed facsimile thereof), with all required signature
guarantees, or, in the case of a book-entry transfer, an Agent's Message, and
(iii) any other documents required by the Letter of Transmittal.
 
    BACKUP FEDERAL INCOME TAX WITHHOLDING.  TO PREVENT "BACKUP" WITHHOLDING WITH
RESPECT TO PAYMENT OF THE PURCHASE PRICE OF SHARES PURCHASED PURSUANT TO THE
OFFER OR PURSUANT TO THE MERGER, EACH STOCKHOLDER MUST EITHER PROVIDE THE
DEPOSITARY WITH SUCH STOCKHOLDER'S CORRECT TAXPAYER IDENTIFICATION NUMBER
("TIN") AND CERTIFY THAT SUCH STOCKHOLDER IS NOT SUBJECT TO BACKUP FEDERAL
INCOME TAX WITHHOLDING BY COMPLETING THE SUBSTITUTE FORM W-9 INCLUDED IN THE
LETTER OF TRANSMITTAL OR ESTABLISH SOME OTHER EXEMPTION TO BACKUP WITHHOLDING.
FOREIGN HOLDERS MUST SUBMIT A COMPLETED FORM W-8 TO AVOID BACKUP WITHHOLDING.
THIS FORM MAY BE OBTAINED FROM THE DEPOSITARY. SEE INSTRUCTIONS 8 AND 9 SET
FORTH IN THE LETTER OF TRANSMITTAL AND SECTION 5--"CERTAIN UNITED STATES FEDERAL
INCOME TAX CONSIDERATIONS".
 
    EXAMINATION OF VALIDITY.  All questions as to the form of documents and the
validity, eligibility (including time of receipt) and acceptance for payment of
any tender of Shares will be determined by the Offeror, in its sole discretion,
and whose determination will be final and binding on all parties. The Offeror
reserves the absolute right to reject any or all tenders of any Shares that are
determined by it not to be in proper form or the acceptance of or payment for
which may, in the opinion of the Offeror, be unlawful. The Offeror also reserves
the absolute right to waive any of the conditions of the Offer, subject to the
limitations set forth in the Merger Agreement, or any defect or irregularity in
the tender of any Shares. The Offeror's interpretation of the terms and
conditions of the Offer (including the Letter of Transmittal and the
Instructions to the Letter of Transmittal) will be final and binding on all
parties. No tender of Shares will be deemed to have been validly made until all
defects and irregularities have been cured or waived. None of the Offeror, the
Parent, the Dealer Manager, the Depositary, the Information Agent or any other
person will be under any duty to give notification of any defects or
irregularities in tenders or incur any liability for failure to give any such
notification.
 
    OTHER REQUIREMENTS.  By executing the Letter of Transmittal as set forth
above (including through delivery of an Agent's Message), a tendering
stockholder irrevocably appoints designees of the Offeror as such stockholder's
attorneys-in-fact and proxies, each with full power of substitution, in the
manner set forth in the Letter of Transmittal, to the full extent of such
stockholder's rights with respect to the Shares tendered by such stockholder and
accepted for payment by the Offeror (and any and all other Shares or other
securities issued or issuable in respect of such Shares on or after June 10,
1998). All such powers of attorney and proxies shall be considered coupled with
an interest in the tendered Shares. This appointment is effective when, and only
to the extent that, the Offeror accepts for payment the Shares deposited with
the Depositary. Upon acceptance for payment, all prior powers of attorney and
proxies given by the stockholder with respect to such Shares or other securities
or rights will, without further action, be revoked and no subsequent proxies may
be given or written consent executed (and, if given or executed, will not be
 
                                       7
<PAGE>
deemed effective). The designees of the Offeror will, with respect to the Shares
and other securities or rights, be empowered to exercise all voting and other
rights of such stockholder as they in their sole judgment deem proper in respect
of any annual or special meeting of the Company's stockholders, or any
adjournment or postponement thereof. The Offeror reserves the right to require
that, in order for Shares to be deemed validly tendered, immediately upon the
Offeror's payment for such Shares, the Offeror must be able to exercise full
voting and other rights with respect to such Shares and the other securities or
rights issued or issuable in respect of such Shares, including voting at any
meeting of stockholders (whether annual or special or whether or not adjourned)
in respect of such Shares.
 
    A tender of Shares pursuant to any one of the procedures described above
will constitute the tendering stockholder's acceptance of the terms and
conditions of the Offer, as well as the tendering stockholder's representation
and warranty that (i) such stockholder has the full power and authority to
tender, sell, assign and transfer the tendered Shares (and any and all other
Shares or other securities issued or issuable in respect of such Shares on or
after June 10, 1998) and (ii) when the same are accepted for payment by the
Offeror, the Offeror will acquire good and unencumbered title thereto, free and
clear of all liens, restrictions, charges and encumbrances and not subject to
any adverse claims. The Offeror's acceptance for payment of Shares tendered
pursuant to the Offer will constitute a binding agreement between the tendering
stockholder and the Offeror upon the terms and subject to the conditions of the
Offer.
 
4. WITHDRAWAL RIGHTS.
 
    Except as otherwise provided in this Section 4--"Withdrawal Rights", tenders
of Shares made pursuant to the Offer are irrevocable. Shares tendered pursuant
to the Offer may be withdrawn at any time prior to the Expiration Date and,
unless theretofore accepted for payment pursuant to the Offer, may also be
withdrawn at any time after Friday, August 14, 1998. If purchase of or payment
for Shares is delayed for any reason or if the Offeror is unable to purchase or
pay for Shares for any reason, then, without prejudice to the Offeror's rights
under the Offer, tendered Shares may be retained by the Depositary on behalf of
the Offeror and may not be withdrawn except to the extent that tendering
stockholders are entitled to withdrawal rights as set forth in this Section
4--"Withdrawal Rights", subject to Rule 14e-1(c) under the Exchange Act, which
provides that no person who makes a tender offer shall fail to pay the
consideration offered or return the securities deposited by or on behalf of
security holders promptly after the termination or withdrawal of the Offer.
 
    For a withdrawal of Shares tendered pursuant to the Offer to be effective, a
written, telegraphic, telex or facsimile transmission notice of withdrawal must
be timely received by the Depositary at the address set forth on the back cover
of this Offer to Purchase and must specify the name of the person who tendered
the Shares to be withdrawn, the number of Shares to be withdrawn and the name of
the registered holders, if different from the name of the person who tendered
such Shares. If certificates for Shares to be withdrawn have been delivered or
otherwise identified to the Depositary, then, prior to the release of such
certificates, the serial numbers shown on such certificates must be submitted to
the Depositary and, unless such Shares have been tendered by an Eligible
Institution, the signatures on the notice of withdrawal must be guaranteed by an
Eligible Institution. If Shares have been tendered pursuant to the procedures
for book-entry transfer set forth in Section 3--"Procedure for Tendering
Shares", any notice of withdrawal must also specify the name and number of the
account at the Book-Entry Transfer Facility to be credited with the withdrawn
Shares and must otherwise comply with such Book-Entry Transfer Facility's
procedures. All questions as to the form and validity (including time of
receipt) of notices of withdrawal will be determined by the Offeror, in its sole
discretion, and whose determination will be final and binding on all parties.
None of the Offeror, the Parent, the Dealer Manager, the Depositary, the
Information Agent or any other person will be under any duty to give
notification of any defects or irregularities in any notice of withdrawal or
incur any liability for failure to give any such notification.
 
                                       8
<PAGE>
    Any Shares properly withdrawn will be deemed not validly tendered for
purposes of the Offer, but may be retendered at any subsequent time prior to the
Expiration Date by following any of the procedures described in Section
3--"Procedure for Tendering Shares".
 
5. CERTAIN UNITED STATES FEDERAL INCOME TAX CONSIDERATIONS.
 
    The following is a summary of certain United States federal income tax
considerations of the Offer and the Merger to holders whose Shares are purchased
pursuant to the Offer or whose Shares are converted to cash in the Merger
(including pursuant to the exercise of appraisal rights). The discussion is for
general information only and does not purport to consider all aspects of United
States federal income taxation that may be relevant to holders of Shares. The
discussion is based on current provisions of the Internal Revenue Code of 1986,
as amended (the "Code"), existing, proposed and temporary regulations
promulgated thereunder and administrative and judicial interpretations thereof,
all of which are subject to change. The discussion applies only to holders of
Shares in whose hands Shares are capital assets within the meaning of Section
1221 of the Code, and may not apply to Shares received pursuant to the exercise
of employee stock options or otherwise as compensation, or to certain types of
holders of Shares (such as insurance companies, tax-exempt organizations and
broker-dealers) who may be subject to special rules under the United States
federal income tax laws. This discussion does not discuss the United States
federal income tax consequences to a holder of Shares who, for United States
federal income tax purposes, is a non-resident alien individual, a foreign
corporation, a foreign partnership or a foreign estate or trust, nor does it
consider the effect of any foreign, state or local tax laws.
 
    BECAUSE INDIVIDUAL CIRCUMSTANCES MAY DIFFER, EACH HOLDER OF SHARES SHOULD
CONSULT SUCH HOLDER'S OWN TAX ADVISOR TO DETERMINE THE APPLICABILITY OF THE
RULES DISCUSSED BELOW TO SUCH HOLDER AND THE PARTICULAR TAX EFFECTS TO SUCH
HOLDER OF THE OFFER AND THE MERGER, INCLUDING THE APPLICATION AND EFFECT OF
STATE, LOCAL AND OTHER INCOME TAX LAWS.
 
    The receipt of cash for Shares pursuant to the Offer or the Merger will be a
taxable transaction for United States federal income tax purposes. In general,
for United States federal income tax purposes, a holder of Shares will recognize
gain or loss equal to the difference between (i) the holder's adjusted tax basis
in the Shares sold pursuant to the Offer or converted to cash in the Merger and
(ii) the amount of cash received therefor. Gain or loss must be determined
separately for each block of Shares (i.e., Shares acquired at the same cost in a
single transaction) sold pursuant to the Offer or converted to cash in the
Merger. Assuming that Shares are held as a capital asset, such gain or loss will
be a capital gain or loss. Any such capital gain will be a long-term capital
gain taxable to a non-corporate holder at a maximum rate of 20% if the holder's
Shares have been held for more than 18 months on the date of sale (in the case
of the Offer) or the Effective Time of the Merger (in the case of the Merger); a
long-term capital gain taxable to a non-corporate holder at a maximum rate of
28% if the Shares have been held for more than one year but not more than 18
months on the date of the sale (or the Effective Time of the Merger) and a
short-term capital gain taxable to a non-corporate holder at a maximum rate of
up to 39.6% if the Shares have been held for one year or less on the date of
sale (or the Effective Time of the Merger).
 
    Payments in connection with the Offer or the Merger may be subject to
"backup withholding" at a rate of 31%, unless a holder of Shares (i) is a
corporation or comes within certain exempt categories and, when required,
demonstrates this fact or (ii) provides a correct TIN to the payor, certifies as
to no loss of exemption from backup withholding and otherwise complies with
applicable requirements of the backup withholding rules. A holder who does not
provide a correct TIN may be subject to penalties imposed by the Internal
Revenue Service. Any amount paid as backup withholding does not constitute an
additional tax and will be creditable against the holder's United States federal
income tax liability. Each holder of Shares should consult with his or her own
tax advisor as to his or her qualification for exemption from backup withholding
and the procedure for obtaining such exemption. Holders tendering their Shares
in the Offer may prevent backup withholding by completing the Substitute Form
W-9 included in the Letter of Transmittal. See Section 3--"Procedure for
Tendering Shares." Similarly, holders who convert their Shares
 
                                       9
<PAGE>
into cash in the Merger may prevent backup withholding by completing a
Substitute Form W-9 and submitting it to the paying agent for the Merger.
 
6. PRICE RANGE OF SHARES; DIVIDENDS.
 
    The Shares are traded in the over-the-counter market, with daily quotations
reported on the NASDAQ quotation system. The following table sets forth for the
periods indicated the high and low sales prices and dividends per Share as
reported in the Company's Form 10-K for the fiscal year ended December 31, 1997,
the Company's Form 10-Q for the first quarter ended March 31, 1998 and by
NASDAQ:
 
<TABLE>
<CAPTION>
                                                                                    HIGH        LOW     DIVIDENDS
                                                                                  ---------  ---------  ---------
<S>                                                                               <C>        <C>        <C>
Year Ended December 31, 1996:
First Quarter...................................................................         401/2        361/4      $.30
Second Quarter..................................................................         391/2        33       .30
Third Quarter...................................................................         39         323/4       .30
Fourth Quarter..................................................................         361/2        333/4       .30
Year Ended December 31, 1997:
First Quarter...................................................................         351/2        331/2      $.31
Second Quarter..................................................................         381/2        34       .31
Third Quarter...................................................................         50         373/8       .31
Fourth Quarter..................................................................         541/4        46       .31
Year Ended December 31, 1998:
First Quarter...................................................................         661/2        441/2      $.32(1)
</TABLE>
 
(1) Does not reflect the special dividend of 878,175 shares of Gradco Systems,
    Inc. which was distributed to the Company's stockholders on March 20, 1998.
 
    On February 24, 1998, the last full trading day prior to the public
announcement of the Company's initiation of the process to sell the Company, the
closing price per Share as reported on NASDAQ was $46.50. On June 9, 1998, the
last full trading day prior to the announcement of the Offer, the closing price
per Share as reported on NASDAQ was $67.50.
 
7. CERTAIN EFFECTS OF THE TRANSACTION.
 
    The purchase of the Shares by the Offeror pursuant to the Offer will reduce
the number of Shares that might otherwise trade publicly and will reduce the
number of holders of Shares, which will adversely affect the liquidity and
market value of the remaining Shares held by stockholders other than the
Offeror. The Company has advised the Offeror that, as of April 16, 1998, there
were approximately 442 stockholders of record and approximately 2,500 beneficial
owners of the Shares.
 
    MARKET FOR SHARES.  Depending upon the aggregate market value and per Share
price of any Shares not purchased pursuant to the Offer, the Shares may no
longer meet the standards for continued inclusion on the NASDAQ Stock Market
("NASDAQ") which requires that an issuer have at least 750,000 publicly held
shares with a market value of five million dollars held by at least 400
stockholders holding round lots and have net tangible assets of at least four
million dollars. If these standards are not met, the Shares might nevertheless
continue to be included on NASDAQ with quotations published on the NASDAQ's
"additional list" or in one of the "local lists." However, if the number of
holders of shares of common stock falls below 400, or if the number of publicly
held shares of common stock falls below 750,000, or if there are not at least
two market makers for such shares, NASDAQ rules provide that the common stock
would no longer be "qualified" for NASDAQ reporting, and NASDAQ would cease to
provide any quotations. Shares held directly or indirectly by an officer or
director of the Company, or by any beneficial owner of more than 10% of the
Shares, ordinarily will not be considered as being publicly held for this
purpose. If, as a result of the purchase of Shares pursuant to the Offer or
otherwise, the Common Stock no longer meets the requirements for continued
inclusion in any other tier of NASDAQ, and the Common Stock is no longer
included in any tier of NASDAQ, the market for such Shares could be adversely
affected.
 
                                       10
<PAGE>
    In the event the Common Stock no longer meets the requirements for inclusion
in any tier of NASDAQ, quotations might still be available from other sources.
The extent of the public market for such Shares and availability of such
quotations would, however, depend upon the remaining number of holders of such
Shares at such time, the interest in maintaining a market in the Shares on the
part of securities firms, the possible termination of registration under the
Exchange Act, as described below, and other factors.
 
    EXCHANGE ACT REGISTRATION.  The Shares are currently registered under the
Exchange Act. Such registration may be terminated upon application by the
Company to the Commission if there are fewer than 300 record holders of Shares.
It is the intention of the Offeror to seek to cause an application for such
termination to be made as soon after consummation of the Offer as the
requirements for termination of registration of the Shares are met. If such
registration were terminated, the Company would no longer legally be required to
disclose publicly in proxy materials distributed to stockholders the information
which it now must provide under the Exchange Act or to make public disclosure of
financial and other information in annual, quarterly and other reports required
to be filed with the Commission under the Exchange Act, and the officers,
directors and 10% stockholders of the Company would no longer be subject to the
"short-swing" insider trading reporting and profit recovery provisions of the
Exchange Act. Furthermore, if such registration were terminated, persons holding
"restricted securities" of the Company may be deprived of their ability to
dispose of such securities under Rule 144 promulgated under the Securities Act
of 1933, as amended (the "Securities Act").
 
    MARGIN REGULATIONS.  The Shares are currently "margin securities" under the
regulations of the Board of Governors of the Federal Reserve System (the
"Federal Reserve Board"), which has the effect, among other things, of allowing
brokers to extend credit on the collateral of the Shares. Depending upon factors
similar to those described above regarding listing and market quotations, it is
possible that, following the consummation of the Offer, the Shares would no
longer constitute "margin securities" for the purposes of the margin regulations
of the Federal Reserve Board and therefore could no longer be used as collateral
for loans made by brokers. If registration of Shares under the Exchange Act were
terminated, the Shares would no longer be "margin securities."
 
8. CERTAIN INFORMATION CONCERNING THE COMPANY.
 
    Except as otherwise set forth herein, the information concerning the Company
contained in this Offer to Purchase, including financial information, has been
furnished by the Company or has been taken from or based upon publicly available
documents and records on file with the Commission and other public sources.
Although neither the Offeror nor the Parent has any knowledge that would
indicate that statements contained herein based upon such information or
documents are untrue, neither the Offeror, the Parent nor the Dealer Manager
assumes any responsibility for the accuracy or completeness of the information
concerning the Company, furnished by the Company, or contained in such documents
and records or for any failure by the Company to disclose events which may have
occurred or may affect the significance or accuracy of any such information but
which are unknown to the Offeror or the Parent.
 
    The Company is a Delaware corporation with its principal executive offices
located at 233 Spring Street, New York, New York. The Company is a leading
publisher of scientific, technical and medical ("STM") journals and books and a
niche information service provider specializing in patent information. The
Company has operating offices in New York, Delaware, North Carolina, London and
Moscow.
 
    Set forth below is certain summary consolidated financial data with respect
to the Company excerpted from the Company's annual report on Form 10-K for the
fiscal year ended December 31, 1997 and quarterly report on Form 10-Q for the
fiscal quarter ended March 31, 1998. More comprehensive financial information is
included in the reports and other documents filed by the Company with the
Commission, and the following summary is qualified in its entirety by reference
to the reports and other documents and all the financial information (including
any related notes) contained in the Company's annual reports on Form 10-K and
quarterly reports on Form 10-Q. Such reports and other documents should be
available for inspection and copies thereof should be obtainable in the manner
set forth below.
 
                                       11
<PAGE>
                  SELECTED CONSOLIDATED FINANCIAL INFORMATION
 
<TABLE>
<CAPTION>
                                                         THREE MONTHS ENDED MARCH      TWELVE MONTHS ENDED
                                                                   31,                     DECEMBER 31,
                                                        --------------------------  --------------------------
                                                            1998          1997          1997          1996
                                                        ------------  ------------  ------------  ------------
<S>                                                     <C>           <C>           <C>           <C>
Income:
  Subscriptions, books and other sales, net...........  $ 13,069,025  $ 12,287,468  $ 52,633,994  $ 51,928,884
                                                        ------------  ------------  ------------  ------------
Cost and expenses:
  Cost of sales.......................................     5,289,602     5,243,509    20,709,590    20,953,870
  Royalties...........................................       844,819       832,995     3,484,839     3,874,419
  Selling, general and administrative expenses........     2,686,537     2,589,832    10,813,438    10,659,819
                                                        ------------  ------------  ------------  ------------
                                                           8,820,958     8,666,336    35,007,867    35,488,108
                                                        ------------  ------------  ------------  ------------
Income from Operations................................     4,248,067     3,621,132    17,626,127    16,440,776
Investment income and other:
  Dividend income.....................................        90,842        80,927       268,945       477,539
  Interest income.....................................       719,999       747,869     2,771,821     2,410,037
  Net realized gain on sales of marketable
    securities........................................     4,442,769       202,381           819         7,491
  Net unrealized (loss) gain on marketable
    securities........................................    (7,694,603)   (2,524,800)   (1,227,545)    4,109,291
  Equity in net income of Gradco Systems, Inc.-- Note
    1.................................................       --            --            611,710       374,330
Other investment-related expenses.....................       (57,457)      (56,725)     (327,417)     (539,622)
                                                        ------------  ------------  ------------  ------------
Income from continuing operations before income
  taxes...............................................     1,749,617     2,070,784    19,724,460    23,279,842
Income tax (benefits) provision.......................      (839,000)      711,000     6,900,000     8,598,000
                                                        ------------  ------------  ------------  ------------
Income from continuing operations.....................     2,588,617     1,359,784    12,824,460    14,681,842
Income from discontinued operations, net of income tax
  of $199,000 - Note 2................................       --            --            --            368,501
                                                        ------------  ------------  ------------  ------------
Net income............................................  $  2,588,617  $  1,359,784  $ 12,824,460  $ 15,050,343
                                                        ------------  ------------  ------------  ------------
                                                        ------------  ------------  ------------  ------------
Basic and Diluted Earnings Per share of Common Stock -
  Notes 2 and 3:
  Income from continuing operations...................  $        .74  $        .35  $       3.45  $       3.75
  Income from discontinued operations.................       --            --            --               0.09
                                                        ------------  ------------  ------------  ------------
Net income............................................  $        .74  $        .35  $       3.45  $       3.84
                                                        ------------  ------------  ------------  ------------
                                                        ------------  ------------  ------------  ------------
</TABLE>
 
Note 1.  On March 20, 1998, the Company distributed, as a dividend, to its
         stockholders substantially all of its shares of Gradco Systems, Inc.
 
Note 2.  In December 1995, the Company's Board of Directors adopted a plan to
         discontinue its wholly owned subsidiary, J.S. Canner & Company, Inc.
         ("Canner"), effective October 1996. Canner was engaged in the purchase
         and sale of back issue periodicals to libraries, universities, colleges
         and other users. Net sales of Canner were approximately $1 million for
         the year ended December 31, 1996.
 
Note 3.  Net income per share of Common Stock is computed on the basis of the
         weighted average number of shares outstanding. The number of shares
         used in this computation for the twelve months ended December 31, 1997
         and 1996 is as follows:
 
<TABLE>
<CAPTION>
                                                                          1997       1996
                                                                        ---------  ---------
<S>                                                                     <C>        <C>        <C>        <C>
        Twelve months.................................................  3,721,433  3,915,045
</TABLE>
 
        The number of shares used in this computation for the three months ended
        March 31, 1998 and 1997 is as follows:
 
<TABLE>
<CAPTION>
                                                                          1998       1997
                                                                        ---------  ---------
 
<S>                                                                     <C>        <C>        <C>        <C>
        Three months..................................................  3,510,251  3,871,593
</TABLE>
 
    The Company is subject to the informational requirements of the Exchange Act
and in accordance therewith files periodic reports, proxy statements and other
information with the Commission relating to its business, financial condition
and other matters. The Company is required to disclose in such proxy statements
certain information, as of particular dates, concerning the Company's directors
and officers,
 
                                       12
<PAGE>
their remuneration, stock options granted to them, the principal holders of the
Company's securities and any material interests of such persons in transactions
with the Company. Such reports, proxy statements and other information may be
inspected at the public reference facilities maintained by the Commission at
Room 1024, 450 Fifth Street, N.W., Washington, D.C. 20549, and at the regional
offices of the Commission located at Seven World Trade Center, 13th Floor, New
York, New York 10048 and Citicorp Center, 500 West Madison Street (Suite 400),
Chicago, Illinois 60661. Copies of such material may also be obtained by mail,
at prescribed rates, from the Commission's principal office at 450 Fifth Street,
N.W., Washington, D.C. 20549. The Commission also maintains a World Wide Web
site on the internet at http://www.sec.gov that contains reports and other
information regarding registrants that file electronically with the Commission.
Such material should also be available for inspection at the offices of NASDAQ,
1735 K Street, N.W., Washington D.C. 20006.
 
9. CERTAIN INFORMATION CONCERNING WOLTERS KLUWER, WOLTERS KLUWER INTERNATIONAL,
  WKUS, WK AMERICA, THE PARENT AND THE OFFEROR.
 
    The Offeror is a Delaware corporation which was formed as an acquisition
vehicle in connection with the Offer, the Merger and the other transactions
contemplated by the Merger Agreement and will be merged with and into the
Company pursuant to the Merger. The Offeror is a wholly owned subsidiary of the
Parent, which is a wholly owned subsidiary of WK America, Inc., a Delaware
corporation ("WK America"), which is a wholly owned subsidiary of WKUS. Wolters
Kluwer International Holding B.V., a corporation organized under the laws of the
Netherlands and a wholly owned subsidiary of Wolters Kluwer ("Wolters Kluwer
International"), owns 100% of the outstanding shares of capital stock of WKUS.
Wolters Kluwer International, WKUS and WK America are holding companies formed
by Wolters Kluwer solely for the purpose of holding shares of capital stock of
indirect subsidiaries of Wolters Kluwer.
 
    Pursuant to the WKUS Letter, WKUS has agreed to fund the obligations of the
Parent and the Offeror under the Merger Agreement through available cash
balances and existing bank credit lines of Wolters Kluwer.
 
    Wolters Kluwer is a multidomestic publishing company active in 25 countries.
Core activities are legal and tax publishing, business publishing,
medical/scientific publishing, educational publishing/professional training and
trade publishing for selected markets. Wolters Kluwer has sales of approximately
$2.5 billion. In addition to the Parent, Wolters Kluwer's U.S. holdings include
Aspen Publishers, CCH Incorporated, Facts and Comparisons, Legal Information
Services, Lippincott Williams & Wilkins (formerly Waverly, Inc and
Lippincott-Raven Publishers) and Blessing/White. The principal executive offices
of Wolters Kluwer are located at Stadhouderskade 1, 1000 AV, Amsterdam, the
Netherlands. The principal executive office of the Parent and the Offeror is c/o
Kluwer Academic Publishers B.V., Spuiboulevard 50, 3300 AZ, Dordrecht, the
Netherlands.
 
    The name, citizenship, business address, present principal occupation or
employment and five-year employment history of each of the directors and
executive officers of Wolters Kluwer, Wolters Kluwer International, WKUS, WK
America, the Parent and the Offeror are set forth in Schedule I hereto.
 
    Set forth below is certain consolidated financial information regarding
Wolters Kluwer and its subsidiaries. The financial information set forth below
was prepared in accordance with generally accepted accounting principles used in
the Netherlands ("Dutch GAAP"), which differ in certain respects from United
States generally accepted accounting principles ("US GAAP"). The principal
differences include:
 
    - Acquired publishing rights are capitalized. In general, publishing rights
      are considered to have an indefinite economic life, and therefore no
      systematic amortization is applied. Write-offs are taken in the case of
      permanent impairment. Under US GAAP, acquired publishing rights are
      amortized over their estimated life, not to exceed 40 years.
 
                                       13
<PAGE>
    - Pension costs are based on actuarially computed contributions to
      foundations. Under US GAAP, pension costs are actuarially computed in
      accordance with the provisions of Financial Accounting Standard No. 87,
      Employers Accounting for Pensions, and include current service costs,
      interest costs and amortization of prior service costs.
 
    - Post-retirement and post-employment benefits are recorded when
      contributions are made to the plan or at the time of retirement or
      termination for unfunded plans. US GAAP generally requires accrual of such
      costs over the period that the employee provides services to the company.
 
    The consolidated financial statements of Wolters Kluwer are published in
Dutch guilders ("guilders" or "Dfl"). The dollar amounts in the table below have
been translated from guilders at the noon buying rate in New York City for cable
transfers in foreign currencies as certified for customs purposes by the Federal
Reserve Bank in New York City (the "Noon Buying Rate") on December 31, 1997,
which was Dfl2.0278 per $1.00. Such rate may differ from the actual rates used
in the preparation of the consolidated financial statements of Wolters Kluwer as
of and for each of the years in the three-year period ended December 31, 1997,
which are expressed in guilders. The dollar amounts appearing herein may differ
from the actual dollar amounts that were translated into guilders in the
preparation of such financial statements. The following table sets forth, for
the periods and dates indicated, the average, high, low and period-end Noon
Buying Rates for guilders expressed in guilders per $1.00.
 
                             YEARLY EXCHANGE RATES
                                (AMOUNTS IN DFL)
 
<TABLE>
<CAPTION>
                                 YEAR                                   AVERAGE(1)     HIGH        LOW     PERIOD-END
- ----------------------------------------------------------------------  -----------  ---------  ---------  -----------
<S>                                                                     <C>          <C>        <C>        <C>
1994..................................................................      1.8077      1.9750     1.6727      1.7360
1995..................................................................      1.5976      1.7494     1.5192      1.6035
1996..................................................................      1.6889      1.7560     1.6075      1.7271
1997..................................................................      1.9585      2.1177     1.7300      2.0278
1998 (through June 10, 1998)..........................................      2.0449      2.0890     1.9817      2.0260
</TABLE>
 
- ------------------------
 
(1) The average of the Noon Buying Rates on the last business day of each month
    during the relevant period.
 
                                       14
<PAGE>
                      SELECTED CONSOLIDATED FINANCIAL DATA
 
<TABLE>
<CAPTION>
                                                                              YEAR ENDED DECEMBER 31,
                                                                 -------------------------------------------------
                                                                         1997(1)             1996         1995
                                                                 -----------------------  -----------  -----------
                                                                 (CURRENCY IN MILLIONS, EXCEPT PER SHARE AMOUNTS)
<S>                                                              <C>          <C>         <C>          <C>
AMOUNTS IN ACCORDANCE WITH
  DUTCH GAAP
INCOME STATEMENT DATA:
  Revenues.....................................................  US$   2,569    Dfl5,209     Dfl4,315     Dfl2,944
  Operating income.............................................          600       1,217          927          609
  Net income...................................................          286         579          479          452
BALANCE SHEET DATA (AT END OF PERIOD):
  Working capital..............................................  US$    (365)   Dfl (740)    Dfl (484)    Dfl  (21)
  Total assets.................................................        4,099       8,311        6,746        2,074
  Liabilities..................................................        3,204       6,497        5,553        1,341
  Stockholder's equity.........................................          895       1,814        1,193          733
FULLY DILUTED PER SHARE DATA
  Net income...................................................  US$    4.16    Dfl 8.43     Dfl 7.03     Dfl 6.70
</TABLE>
 
- ------------------------
 
(1) Exchange rate based on the Noon Buying Rate on December 31, 1997:
    Dfl2.0278=US$1. Operating income for the year ended December 31, 1997,
    reflects operating income before the amortization of goodwill.
 
    Except as provided in the Merger Agreement, the Purchase Agreements and the
Option Agreement (as defined below) and as otherwise described in this Offer to
Purchase, none of Wolters Kluwer, WKUS, the Parent or the Offeror, or, to the
best knowledge of the Parent and the Offeror, any of the persons listed on
Schedule I hereto, has any contract, arrangement, understanding or relationship
with any other person with respect to any securities of the Company, including,
but not limited to, any contract, arrangement, understanding or relationship
concerning the transfer or the voting of any securities of the Company, joint
ventures, loan or option arrangements, puts or calls, guarantees of loans,
guarantees against loss or the giving or withholding of proxies. Except as set
forth in this Offer to Purchase, none of Wolters Kluwer, WKUS, the Parent or the
Offeror, or, to the best knowledge of the Parent and the Offerer, any of the
persons listed on Schedule I hereto, has had, since January 1, 1995, any
business relationships or transactions with the Company or any of its executive
officers, directors or affiliates that would require reporting under the rules
of the Commission applicable to this Offer to Purchase. Except as set forth in
this Offer to Purchase, since January 1, 1995, there have been no contacts,
negotiations or transactions between Wolters Kluwer, WKUS, the Parent or the
Offeror or any of their respective subsidiaries, or, to the best knowledge of
the Parent and the Offeror, any of the persons listed on Schedule I hereto, and
the Company or its affiliates, concerning a merger, consolidation or
acquisition, tender offer or other acquisition of securities, election of
directors or a sale or other transfer of a material amount of assets. Except as
set forth in this Offer to Purchase, neither the Parent nor the Offeror, nor, to
the best knowledge of the Parent and the Offeror, any of the persons listed on
Schedule I hereto, beneficially owns any Shares or has effected any transactions
in the Shares during the past 60 days.
 
10. SOURCE AND AMOUNT OF FUNDS.
 
    The total amount of funds required by the Offeror and the Parent to
consummate the Offer and the Merger is estimated to be approximately $258
million, which amount excludes related fees and expenses. The Offeror intends to
obtain the required funds from capital contributions and/or loans from Wolters
Kluwer.
 
    It is presently anticipated that funds borrowed will be repaid from
internally generated funds of the Parent or the Company. The Parent may,
however, employ alternative methods for refinancing such borrowings, including,
without limitation, debt financing, depending on prevailing interest rates and
financial and other economic conditions.
 
                                       15
<PAGE>
11. BACKGROUND OF THE OFFER; PAST CONTACTS, TRANSACTIONS OR NEGOTIATIONS WITH
  THE COMPANY.
 
    On February 25, 1998, the Company announced that its Board of Directors had
initiated a process to explore the sale of the Company and that it had retained
Salomon Smith Barney to assist it in seeking prospective buyers. The press
release noted that the Company was motivated by recent consolidation in the
publishing sector.
 
    On April 6, 1998, WKUS entered into a confidentiality agreement with Salomon
Smith Barney on behalf of the Company (the "Confidentiality Agreement") pursuant
to which certain evaluation material concerning the Company would be made
available to WKUS and its affiliates and representatives on a confidential
basis.
 
    On May 5, 1998, the Parent sent a preliminary letter of interest to the
Company indicating its initial interest in purchasing the Company. Such interest
was contingent upon, among other things, the completion of satisfactory
financial and legal due diligence.
 
    On May 11, 1998, Salomon Smith Barney sent to WKUS, as one of three parties
selected to continue in the auction process, a letter (the "Bid Procedures
Letter") governing further procedures for the auction process and a form of
Agreement and Plan of Merger. The parties were invited to submit a firm written
offer to acquire the Company (a "Proposal") and were instructed to submit
Proposals by May 29, 1998. The Bid Procedures Letter instructed the parties to
include in the Proposal the specific amount of consideration offered per share.
Each party was asked to mark changes in the form of the Agreement and Plan of
Merger provided, which had been prepared by the Company, and to include in the
Proposal a statement that such party would be prepared to execute such marked
Agreement and Plan of Merger (with any proposed modifications) in the form
submitted. Pursuant to the Bid Procedures Letter, submission of a Proposal
constituted an agreement to be bound by the terms set forth therein.
 
    On May 18 and May 19, 1998, the Chief Executive Officer of the Parent, other
members of the Parent's and Wolters Kluwer's senior management teams and
representatives of the Parent's legal and financial advisors attended a
presentation hosted by members of the Company's senior management team and its
financial advisor to discuss the Company's business activities and its financial
performance and conducted a site visit of the Company's facilities.
 
    On May 28, 1998, the Executive Board of Wolters Kluwer met and authorized
management of the Parent to make an offer, contingent upon receipt of approval
by the Supervisory Board of Wolters Kluwer, to acquire the Company. WKUS
submitted, on behalf of the Parent, an offer proposal to the Company in the
afternoon of May 29, 1998 (the "Wolters Kluwer Proposal") conditioned upon,
among other things, the Company's agreement to negotiate with the Parent on an
exclusive basis. See Section 13--"The Merger Agreement, the Purchase Agreements,
the Option Agreement and the WKUS Letter".
 
    On the afternoon of June 2, 1998, the Parent's financial advisor discussed
the Wolters Kluwer Proposal with the Company's financial advisor. On June 3,
1998, after the Wolters Kluwer Proposal was revised by WKUS, such revised
proposal was accepted by the Company.
 
    On June 4, 1998, the legal and financial advisors to the Company met with
those of the Parent to negotiate the Merger Agreement, the Purchase Agreements,
the Option Agreement and the WKUS Letter and, subject to final approval and
completion of legal documentation, agreement was reached on all substantive
matters. On that date, the Company executed an exclusivity letter with WKUS
under which the Company agreed not to negotiate the sale of the Company with any
other parties until the earlier of the execution of the Merger Agreement or June
24, 1998 (the "Exclusivity Letter").
 
    On June 9, 1998, the Supervisory Board of Wolters Kluwer met, reviewed the
possible acquisition of the Company with the Executive Board of Wolters Kluwer
and authorized management of the Parent to make an offer to acquire the Company.
 
                                       16
<PAGE>
    The Board of Directors met with the Company's legal and financial advisors
during the morning on June 10, 1998 and determined to accept the revised Wolter
Kluwer Proposal. On the morning of June 10, 1998, the Merger Agreement, the
Purchase Agreements, the Option Agreement and the WKUS Letter were finalized and
executed. On the afternoon of June 10, 1998, public announcements were made in
the United States and the Netherlands.
 
    On June 16, 1998, the Parent and the Offeror commenced the Offer.
 
12. PURPOSE OF THE OFFER AND THE MERGER; PLANS FOR THE COMPANY.
 
    The purpose of the Offer, the Merger, the Merger Agreement, the Purchase
Agreements and the Option Agreement is to enable the Parent to acquire control
of, and the entire equity interest in, the Company. The Offer, the Merger
Agreement, the Purchase Agreements and the Option Agreement are intended to
increase the likelihood that the Merger will be effected as promptly as
practicable.
 
    Under the Delaware GCL and the Certificate of Incorporation of the Company,
any merger (other than a merger effectuated pursuant to the short-form merger
provisions of the Delaware GCL) must be approved by the Board of Directors of
the Company and the affirmative vote of the holders of that number of Shares
which would constitute a majority of the Shares outstanding on a fully diluted
basis. The Board of Directors of the Company has unanimously approved the Offer,
the Merger and the Merger Agreement and the transactions contemplated thereby.
The Company has agreed (if required by applicable law to consummate the Merger)
to take all action necessary to convene a meeting of its stockholders as
promptly as practicable after the consummation of the Offer for the purpose of
obtaining stockholder approval of the Merger. The Parent has agreed that,
subject to applicable law, all Shares owned by the Offeror or any other
subsidiary of the Parent will be voted in favor of the Merger. The stockholders
meeting shall be held as soon as practicable following the purchase of Shares
pursuant to the Offer. If the Offeror owns that number of Shares which would
constitute a majority of the Shares outstanding on a fully diluted basis,
approval of the Merger can be obtained without the affirmative vote of any other
stockholder of the Company. In the event that the Offeror acquires 90% or more
of the Shares, under the Short-form merger provisions of the Delaware GCL the
Parent would be able to effectuate the Merger by appropriate resolutions of the
Boards of Directors of the Offeror and of the Company without any meeting or
action by the stockholders of the Company.
 
    APPRAISAL RIGHTS.  No appraisal rights are available in connection with the
Offer. However, if the Merger is consummated, stockholders of the Company have
certain rights under the Delaware GCL to dissent and demand appraisal of, and
payment in cash of the fair value of, their Shares. Such rights, if the
statutory procedures are complied with, could lead to a judicial determination
of the fair value (excluding any element of value arising from the
accomplishment or expectation of the Merger) required to be paid in cash to such
dissenting holders for their Shares. Any such judicial determination of the fair
value of Shares could be based upon considerations other than or in addition to
the price paid in the Offer and the market value of the Shares, including asset
values and the investment value of the Shares. The value so determined could be
more or less than the purchase price per Share pursuant to the Offer or the
consideration per Share to be paid in the Merger.
 
    In the event that appraisal rights were available, an objecting stockholder
shall cease to have any rights as a stockholder with respect to the Shares
except the right to receive payment of the fair value thereof. The stockholder's
rights may be restored only upon the withdrawal, with the consent of the
Company, of the demand for payment, no filing of a petition for appraisal within
the time required, a determination of the court that the stockholder is not
entitled to an appraisal, or the abandonment or rescission of the transaction to
which the stockholder objected.
 
    The foregoing summary of the rights of objecting stockholders does not
purport to be a complete statement of the procedures to be followed by
stockholders desiring to exercise their dissenters' appraisal
 
                                       17
<PAGE>
rights. The preservation and exercise of dissenters' rights are conditioned on
strict adherence to the applicable provisions of the Delaware GCL.
 
    RULE 13E-3.  The Commission has adopted Rule 13e-3 under the Exchange Act
which is applicable to certain "going private" transactions and which may under
certain circumstances be applicable to the Merger or another business
combination following the purchase of Shares pursuant to the Offer or otherwise
in which the Offeror seeks to acquire the remaining Shares not held by it. The
Offeror believes, however, that Rule 13e-3 will not be applicable to the Merger
if the Merger is consummated within one year after the termination of the Offer
at the same per Share price as paid in the Offer. If applicable, Rule 13e-3
requires, among other things, that certain financial information concerning the
Company and certain information relating to the fairness of the proposed
transaction and the consideration offered to minority stockholders in such
transaction be filed with the Commission and disclosed to stockholders prior to
consummation of the transaction.
 
    PLANS FOR THE COMPANY.  Wolters Kluwer believes that, in today's highly
competitive global scientific publishing markets, marked by a gradual ongoing
shift to electronic publishing, both the quality and the quantity of content
ownership are increasingly important. A strategic alliance between the Parent
and the Company is a natural step towards securing long-term success in the
scientific publishing marketplace. As such, the Parent will continue to evaluate
the business and operations of the Company during the pendency of the Offer and
after the consummation of the Offer and the Merger.
 
13. THE MERGER AGREEMENT, THE PURCHASE AGREEMENTS, THE OPTION AGREEMENT AND THE
  WKUS LETTER.
 
    The following is a summary of certain material provisions of the Merger
Agreement, the Purchase Agreements, the Option Agreement and the WKUS Letter,
copies of which are filed as exhibits to the Schedule 14D-1 and Schedule 13D.
These summaries do not purport to be complete and are qualified in their
entirety by reference to the respective texts of the Merger Agreement, the WKUS
Letter, the Option Agreement and the WKUS Letter. Capitalized terms not
otherwise defined below shall have the meanings set forth in the Merger
Agreement.
 
    THE MERGER AGREEMENT
 
    THE OFFER.  The Merger Agreement provides for the commencement of the Offer
not later than the fifth business day from the public announcement of the
execution of the Merger Agreement. The Merger Agreement also provides that the
Offer shall be subject solely to the condition that there be validly tendered
and not withdrawn prior to the expiration of the Offer that number of Shares
which, when added to any Shares acquired pursuant to the Purchase Agreements
simultaneously with the acceptance of Shares pursuant to the Offer, satisfies
the Minimum Condition, and to the other conditions set forth in Section
14--"Certain Conditions to the Offeror's Obligations" (including the expiration
of applicable waiting periods under the Hart-Scott-Rodino Antitrust Improvements
Act of 1976, as amended (the "HSR Act")). Pursuant to the Merger Agreement,
neither the Parent nor the Offeror may decrease the price per Share or change
the form of consideration payable in the Offer, decrease the number of Shares
sought to be purchased in the Offer, change the conditions set forth in Section
14--"Certain Conditions to the Offeror's Obligations", impose additional
conditions to the Offer or amend any other term of the Offer in any manner
materially adverse to the holders of the Shares. Subject to the terms of the
Offer and the Merger Agreement and the satisfaction or waiver of all the
conditions of the Offer set forth in Section 14-- "Certain Conditions to the
Offeror's Obligations" as of any expiration date of the Offer, the Parent and/or
the Offeror will accept for payment and pay for all Shares validly tendered and
not properly withdrawn pursuant to the Offer as soon as practicable after such
expiration date of the Offer. Notwithstanding the foregoing, the Offeror may,
without the consent of the Company, (i) extend the Offer on one or more
occasions for up to ten business days for each such extension beyond the then
scheduled expiration date (the initial scheduled expiration date being 20
business days following commencement of the Offer), if at the then scheduled
expiration date of the Offer any of the conditions to the Offeror's obligation
to accept
 
                                       18
<PAGE>
for payment and pay for the Shares shall not be satisfied or waived, until such
time as such conditions are satisfied or waived, (ii) increase the Offer Price
and extend the Offer for any period required by any rule, regulation,
interpretation or provision of the Commission or the staff thereof applicable to
the Offer and (iii) extend the Offer for an aggregate period of not more than 10
business days beyond the latest expiration date that would otherwise be
permitted under clause (i) or (ii) of this sentence if there shall not have been
tendered and not withdrawn pursuant to the Offer at least 90% of the outstanding
Shares.
 
    COMPANY ACTIONS.  Pursuant to the Merger Agreement, the Company has agreed
that, as promptly as practicable following the commencement of the Offer, it
will file with the Commission and mail to its stockholders, a
Solicitation/Recommendation Statement on Schedule 14D-9 containing the
recommendation of the Board of Directors that the Company's stockholders accept
the Offer and approve the Merger, subject to the fiduciary duties of the
Company's directors under applicable law and to the provisions of the Merger
Agreement.
 
    THE MERGER.  The Merger Agreement provides that at the Effective Time, the
Offeror shall be merged with and into the Company. Following the Merger, the
separate corporation existence of the Offeror shall cease and the Company shall
continue as the surviving corporation (the "Surviving Corporation"). The Merger
Agreement also provides that at the option of the Parent and provided that such
amendment does not delay the Effective Time, the Merger may be structured so
that the Company shall be merged with and into the Offeror or another direct or
indirect wholly owned subsidiary of the Parent with the Offeror or such other
subsidiary of the Parent continuing as the Surviving Corporation.
 
    Pursuant to the Merger Agreement, the Certificate of Incorporation of the
Company at the Effective Time shall be the Certificate of Incorporation of the
Surviving Corporation. The Merger Agreement also provides that the Bylaws of the
Offeror at the Effective Time shall be the Bylaws of the Surviving Corporation
and that the officers and directors of the Offeror at the Effective Time shall
serve as the initial officers and directors of the Surviving Corporation.
 
    CONVERSION OF SECURITIES.  At the Effective Time, each Share issued and
outstanding immediately prior to the Effective Time (other than any Shares held
by the Parent, the Offeror, any wholly owned subsidiary of the Parent or the
Offeror, or in the treasury of the Company, which shares, by virtue of the
Merger and without any action on the part of the holder thereof, shall be
cancelled and retired and shall cease to exist with no payment being made with
respect thereto, and other than Dissenting Shares) shall be converted into the
right to receive the Offer Price, without interest thereon, upon surrender of
the certificate formerly representing such Share. "Dissenting Shares" means
Shares outstanding immediately prior to the Effective Time and held by a holder
who has not voted in favor of the Merger or consented thereto in writing and who
has demanded appraisal for such Shares in accordance with Section 262 of the
Delaware GCL, if such Section 262 provides for appraisal rights for such Shares
in the Merger.
 
    At the Effective Time, each share of common stock, par value $.01 per share,
of the Offeror issued and outstanding immediately prior to the Effective Time
shall, by virtue of the Merger and without any action on the part of the holder
thereof, be converted into and become one validly issued, fully paid and
non-assessable share of common stock, par value $.10 per share, of the Surviving
Corporation.
 
    REPRESENTATIONS AND WARRANTIES.  In the Merger Agreement, the Company has
made customary representations and warranties to the Parent and the Offeror,
including, but not limited to, representations and warranties as to organization
and qualification, subsidiaries, capital structure, authority to enter into the
Merger Agreement and to consummate the transactions contemplated thereby,
required consents and approvals, filings made by the Company with the Commission
under the Securities Act or the Exchange Act (including financial statements
included in the documents filed by the Company under those acts), absence of
material adverse changes, absence of litigation, employee benefit plans,
environmental laws and regulations, intellectual property, tax matters,
liability insurance and the inapplicability of certain state takeover statutes.
 
                                       19
<PAGE>
    The Offeror and the Parent have also made customary representations and
warranties to the Company, including, but not limited to, representations and
warranties as to organization, authority to enter into the Merger Agreement and
to consummate the transactions contemplated thereby, required consents and
approvals and financing.
 
    COVENANTS RELATING TO THE CONDUCT OF BUSINESS.  The Merger Agreement
provides that during the period from the date of the Merger Agreement to the
Effective Time, the Company will, and will cause each of its Subsidiaries to,
conduct its operations only in the ordinary and usual course of business
consistent with past practice, to preserve intact the business organization of
the Company and each of its Subsidiaries, to keep available the services of its
and their present officers and key employees, and to preserve the good will of
those having business relationships with it. "Subsidiary" means, with respect to
the Parent, the Company or any other person, any corporation, partnership, joint
venture or other legal entity of which the Parent, the Company or such other
person, as the case may be (either alone or through or together with any other
subsidiary), owns, directly or indirectly, stock or other equity interests the
holders of which are generally entitled to more than 50% of the vote for the
election of the board of directors or other governing body of such corporation
or other legal entity. The Company has agreed that, except as otherwise
expressly contemplated by the Merger Agreement, during such period, the Company
will not, and the Company will not permit any of its Subsidiaries to, without
the prior written consent of the Parent:
 
        (a) adopt any amendment to its Certificate of Incorporation or By-laws
    or comparable organizational documents;
 
        (b) except for issuances of capital stock of the Company's Subsidiaries
    to the Company or a wholly owned Subsidiary of the Company, issue, reissue,
    pledge or sell, or authorize the issuance, reissuance, pledge or sale of (i)
    additional shares of capital stock of any class, or securities convertible
    into, exchangeable for or evidencing the right to substitute for, capital
    stock of any class, or any rights, warrants, options, calls, commitments or
    any other agreements of any character, to purchase or acquire any capital
    stock or any securities or rights convertible into, exchangeable for, or
    evidencing the right to subscribe for, capital stock, or (ii) any other
    securities in respect of, in lieu of, or in substitution for, Shares
    outstanding on the date of the Merger Agreement;
 
        (c) declare, set aside or pay any dividends or other distribution
    (whether in cash, securities or property or any combination thereof) in
    excess of the regular quarterly dividend in an amount equal to the last paid
    regular quarterly cash dividend paid by the Company which would normally be
    paid approximately three months after such last paid regular quarterly
    dividend was paid, if any such dividends are declared and paid;
 
        (d) split, combine, subdivide, reclassify or redeem, purchase or
    otherwise acquire, or propose to redeem or purchase or otherwise acquire,
    any shares of its capital stock, or any of its other securities;
 
        (e) except for (i) increases in salary and wages granted to officers and
    employees of the Company or its Subsidiaries in conjunction with promotions
    or other changes in job status or normal compensation reviews (within the
    amounts projected in the Company's 1998 operating plan previously provided
    to the Parent) in the ordinary course of business consistent with past
    practice, or (ii) increases in salary, wages and benefits to employees of
    the Company pursuant to collective bargaining agreements in effect on the
    date of the Merger Agreement, increase the compensation or fringe benefits
    payable or to become payable to its directors, officers or employees
    (whether from the Company or any of its Subsidiaries), or pay or award any
    benefit not required by any existing plan or arrangement (including, without
    limitation, the granting of stock options, stock appreciation rights, shares
    of restricted stock or performance units) or grant any additional severance
    or termination pay to (other than as required by existing agreements or
    policies listed on Schedule 4.12(i) to the Merger Agreement), or enter into
    any employment or severance agreement with, any director, officer or other
    employee of the Company or any of its Subsidiaries or, except pursuant to
    arrangements disclosed in
 
                                       20
<PAGE>
    Schedule 4.12(i) to the Merger Agreement, establish, adopt, enter into,
    amend, accelerate any rights or benefits or waive any performance or vesting
    criteria under any collective bargaining, bonus, profit sharing, thrift,
    compensation, stock option, restricted stock, pension, retirement, savings,
    welfare, deferred compensation, golden parachute, employment, termination,
    severance or other employee benefit plan, agreement, trust, fund, policy or
    arrangement for the benefit or welfare of any directors, officers or current
    or former employees (any of the foregoing being an "Employee Benefit
    Arrangement"), except in each case to the extent required by applicable law
    or regulation;
 
        (f) acquire, sell, lease or dispose of any assets or securities which
    are material to the Company and its Subsidiaries, or enter into any
    commitment to do any of the foregoing or enter into any material commitment
    or transaction, other than transactions between a wholly owned Subsidiary of
    the Company and the Company or another wholly owned Subsidiary of the
    Company;
 
        (g) (i) incur, assume or pre-pay any long-term debt or incur or assume
    any short-term debt, (ii) assume except in the ordinary course of business
    consistent with past practice, guarantee, endorse or otherwise become liable
    or responsible (whether directly, contingently or otherwise) for the
    obligations of any other person or (iii) make any advances except in the
    ordinary course of business consistent with past practice (other than
    advances to Salomon Smith Barney required under a letter agreement between
    Salomon Smith Barney and the Company dated February 28, 1998), loans or
    capital contributions to, or investments in, any other person (except for
    investments in short term interest bearing instruments purchased with excess
    cash of the Company, and for loans, advances, capital contributions or
    investments between any wholly owned Subsidiary of the Company and the
    Company or another wholly owned Subsidiary of the Company);
 
        (h) settle or compromise any material suit or claim or material
    threatened suit or claim;
 
        (i) other than in the ordinary course of business consistent with past
    practice, (i) modify, amend or voluntarily terminate any contract, (ii)
    waive, release, relinquish or assign any contract (or any rights of the
    Company or any of its Subsidiaries thereunder), right or claim, or (iii)
    cancel or forgive any indebtedness owed to the Company or any of its
    Subsidiaries except for any indebtedness relating to goods properly returned
    to the Company;
 
        (j) make any tax election not required by law or settle or compromise
    any tax liability, in either case that is material to the Company and its
    Subsidiaries;
 
        (k) make any material change, other than in the ordinary course of
    business and consistent with past practice or as required by applicable law,
    regulation or change in generally accepted accounting principles, applied by
    the Company (including tax accounting principles);
 
        (l) release any person or entity from, or waive any provision of, any
    standstill agreement to which it is a party or any confidentiality agreement
    between it and another person or entity; or
 
       (m) agree in writing or otherwise to take any of the foregoing actions or
    any action which would cause any representation or warranty in the Merger
    Agreement to be or become untrue or incorrect in any material respect.
 
    HSR ACT.  Pursuant to the Merger Agreement, each of the Company and the
Parent agreed to use its reasonable best efforts to file as soon as practicable
notifications under the HSR Act with respect to Purchaser's exercise of the
Company Option and to respond as prompty as practicable to any inquiries
received from the Federal Trade Commission (the "FTC") and the Antitrust
Division of the Department of Justice (the "Antitrust Division") for additional
information or documentation and to respond as prompty as practicable to all
inquiries and requests received from any State Attorney General or other
Governmental Entity in connection with antitrust matters. Pursuant to the Merger
Agreement, each of the Company and Parent further agree to take all reasonable
actions necessary to file any other forms or
 
                                       21
<PAGE>
notifications which may be required by any foreign Governmental Entity and to
obtain any approvals which may be required in connection therewith.
 
    NO SOLICITATION.  The Company has agreed in the Merger Agreement that
neither the Company, its Subsidiaries nor any of their respective officers,
directors and consultants (including, but not limited to, investment bankers,
attorneys and accountants) shall, directly or indirectly, encourage, solicit,
participate in or initiate discussions or negotiations with, or provide any
information to, any corporation, partnership, person or other entity or group
(other than the Offeror, any of its affiliates or representatives) concerning
any proposal or offer to acquire all or a substantial part of the business or
properties of the Company or any of its Subsidiaries or any capital stock of the
Company or any of its Subsidiaries, whether by merger, tender offer, exchange
offer, sale of assets or similar transaction involving the Company or any
Subsidiary, division or operating or principal business unit of the Company (an
"Acquisition Proposal"), except that nothing contained in the Merger Agreement
shall prohibit the Company or the Company's Board of Directors from (i) taking
and disclosing to the Company's stockholders a position with respect to a tender
or exchange offer by a third party pursuant to Rules 14d-9 and 14e-2 promulgated
under the Exchange Act, or (ii) making such disclosure to the Company's
stockholders as, in the good faith judgment of the Board of Directors, after
receiving advice from legal counsel to the Company, is required under applicable
law; provided that the Company may not, except as permitted by the Merger
Agreement, withdraw or modify its position with respect to the Offer or the
Merger or approve or recommend, or propose to approve or recommend any
Acquisition Proposal, or enter into any agreement with respect to any
Acquisition Proposal. The Merger Agreement also provides that except as
permitted by the Merger Agreement, the Company shall, and shall cause each of
its Subsidiaries to, immediately cease and cause to be terminated any existing
activities, discussions or negotiations by the Company, any of its Subsidiaries
or any officer, director, employee or affiliate of, or investment banker,
attorney, accountant or other advisor or representative of, the Company or any
of its Subsidiaries with parties conducted prior to the date of the Merger
Agreement with respect to any of the foregoing.
 
    Pursuant to the Merger Agreement, the Company may furnish information
concerning the Company and its Subsidiaries to any corporation, partnership,
person or other entity or group pursuant to appropriate confidentiality
agreements with terms substantially similar to those contained in the
Confidentiality Agreement, and may negotiate and participate in discussions and
negotiations with such entity or group concerning an Acquisition Proposal if (i)
such entity or group, which has not been solicited by or on behalf of the
Company after the date of the Merger Agreement, has submitted a bona fide
written proposal to the Company relating to the acquisition of all or
substantially all of the business or properties of the Company and its
subsidiaries or the acquisition of all of the capital stock of the Company with
respect to which the Board of Directors of the Company concludes in good faith,
after consulting with a nationally recognized investment banking firm (including
but not limited to Salomon Smith Barney), (A) the proposal is more favorable to
the Company's stockholders (in their capacities as stockholders), from a
financial point of view, than the Offer and the Merger and (B) the bidder is
fully capable of completing the transaction in accordance with the terms of such
proposal, and (ii) in the good faith opinion of the Board of Directors of the
Company, only after receipt of written advice from legal counsel to the Company,
the failure to provide such information or access or to engage in such
discussions or negotiations would cause the Board of Directors of the Company to
violate its fiduciary duties to the Company's stockholders under applicable law
(an Acquisition Proposal which satisfies clauses (i) and (ii) being referred to
herein as a "Superior Proposal"). The Merger Agreement requires the Company to
provide reasonable notice to the Offeror to the effect that it has received an
Acquisition Proposal, including its terms and conditions (but excluding the
identity of the party or parties making such acquisition Proposal, unless the
terms and conditions of such Acquisition Proposal contain a purchase price that
includes stock of such party or parties. At any time after 48 hours following
notification to the Offeror of the Company's intent to do so (which notification
shall include the identity of the bidder and the material terms and conditions
of the proposal) and if the Company has otherwise complied with the terms of the
Merger Agreement, the Board of Directors of the Company may withdraw or modify
its recommendation of the Offer and may cause the Company to enter
 
                                       22
<PAGE>
into an agreement with respect to a Superior Proposal, provided it shall
concurrently with entering into such agreement pay or cause to be paid to the
Offeror the Termination Fee (as defined below) plus any amount payable at the
time for reimbursement of expenses.
 
    INDEMNIFICATION.  The Merger Agreement provides that from and after the
consummation of the Offer, the Parent and the Offeror shall indemnify and hold
harmless each person who is, or has been at any time prior to the date of the
Merger Agreement or who becomes prior to the Effective Time, an officer,
director or employee of the Company or any of its Subsidiaries (collectively,
the "Indemnified Parties" and individually, the "Indemnified Party") against all
losses, liabilities, expenses, claims or damages in connection with any claim,
suit, action, proceeding or investigation based in whole or in part on the fact
that such Indemnified Party is or was a director, officer or employee of the
Company or any of its Subsidiaries and arising out of acts or omissions
occurring prior to and including the Effective Time (including but not limited
to the transactions contemplated by the Merger Agreement) to the fullest extent
permitted by the Delaware GCL, for a period of not less than six years following
the Effective Time.
 
    Pursuant to the Merger Agreement, the Parent agrees to cause the Certificate
of Incorporation and Bylaws of the Surviving Corporation and its Subsidiaries to
include the provisions for the limitation of liability of directors and
indemnification of the Indemnified Parties to the fullest extent permitted under
applicable law and shall not permit the amendment of such provisions in any
manner adverse to the Indemnified Parties, as the case be, without the prior
written consent of such persons, for a period of six years from and after the
date of the Merger Agreement.
 
    BOARD REPRESENTATION.  The Merger Agreement provides that promptly upon the
purchase of Shares by the Parent or the Offeror or any of its Subsidiaries
pursuant to the Offer and/or pursuant to any of the Purchase Agreements, which
Shares represent at least a majority of the outstanding Shares, the Offeror
shall be entitled to designate such number of directors, rounded up to the next
whole number, on the Board of Directors of the Company as is equal to the
product of the total number of directors on the Board of Directors of the
Company (giving effect to the directors designated by the Offeror pursuant to
this sentence) multiplied by the percentage that the number of Shares so
accepted for payment bears to the total number of Shares then outstanding. In
furtherance thereof, the Company has agreed, upon request of the Offeror, to use
its reasonable best efforts promptly either to increase the size of its Board of
Directors or secure the resignations of such number of its incumbent directors,
or both, as is necessary to enable the Offeror's designees to be so elected to
the Company's Board of Directors, and shall take all actions available to the
Company to cause the Offeror's designees to be so elected. At such time, the
Company shall, if requested by the Offeror, also cause persons designated by the
Offeror to constitute at least the same percentage (rounded up to the next whole
number) as is on the Company's Board of Directors of (i) each committee of the
Company's Board of Directors, (ii) each board of directors (or similar body) of
each Subsidiary of the Company and (iii) each committee (or similar body) of
each such board. Subject to applicable law, the Company has agreed to take all
action requested by the Parent or the Offeror which is reasonably necessary to
effect any such election, including mailing to its stockholders the information
required by Section 14(f) of the Exchange Act and Rule 14f-1 promulgated
thereunder.
 
    The Merger Agreement also provides that in the event the Offeror's designees
are elected to the Company's Board of Directors, until the Effective Time, the
Company's Board of Directors shall have at least two directors who are directors
on the date of the Merger Agreement ("Independent Directors"), provided that, in
such event, if the number of Independent Directors shall be reduced below two
for any reason whatsoever, any remaining Independent Directors (or Independent
Director, if there be only one remaining) shall be entitled to designate persons
to fill such vacancies who shall be deemed to be Independent Directors for
purposes of the Merger Agreement or, if no Independent Directors then remains,
the other directors shall designate two persons to fill such vacancies who shall
not be stockholders, affiliates or associates of the Offeror or the Parent and
such persons shall be deemed to be Independent Directors for purposes of the
Merger Agreement.
 
                                       23
<PAGE>
    CONDITIONS PRECEDENT.  The Merger Agreement provides that the respective
obligations of the Parent, the Offeror and the Company to consummate the Merger
and the transactions contemplated by the Merger Agreement are subject to the
satisfaction, at or before the Effective Time, of each of the following
conditions: (a) if required by the Delaware GCL, the stockholders of the Company
shall have duly approved the transactions contemplated by the Merger Agreement:
(b) the consummation of the Merger shall not be restrained, enjoined or
prohibited by any order, judgment, decree, injunction or ruling of a court of
competent jurisdiction or any Governmental Entity and there shall not have been
any statute, rule or regulation enacted, promulgated or deemed applicable to the
Merger by any Governmental Entity which prevents the consummation of the Merger:
and (c) the Parent and/or the Offeror shall have purchased all Shares validly
tendered and not withdrawn pursuant to the Offer; PROVIDED, HOWEVER, that this
condition shall not be applicable to the obligations of the Parent or the
Offeror if the Parent and/or the Offeror fails to purchase Shares tendered
pursuant to the Offer in violation of the terms of the Merger Agreement or the
Offer.
 
    TERMINATION.  The Merger Agreement provides that it may be terminated and
the Merger contemplated thereunder may be abandoned at any time prior to the
Effective Time, notwithstanding approval thereof by the stockholders of the
Company (with any termination by the Parent also being an effective termination
by the Offeror): (a) by mutual consent of the Parent and the Company; (b) by the
Parent or the Company: (i) if any court or Governmental Entity shall have issued
an order, decree or ruling or taken any other action (which order, decree,
ruling or other action the parties to the Merger Agreement are to use their
reasonable best efforts to lift) restraining, enjoining or otherwise prohibiting
the Merger and such order, decree, ruling or other action shall have become
final and nonappealable; or (ii) if (x) the Offer shall have expired without any
Shares being purchased therein or (y) the Offeror shall not have accepted for
payment all Shares tendered pursuant to the Offer by March 31, 1999; PROVIDED,
HOWEVER, that the right to terminate the Merger Agreement under this clause
shall not be available to any party whose failure to fulfill any obligation
under the Merger Agreement has been the cause of, or resulted in, the failure of
the Offeror, to purchase the Shares pursuant to the Offer on or prior to such
date; (c) by the Company: (i) if the Parent and/or the Offeror fails to commence
the Offer; provided, that the Company may not terminate the Merger Agreement
pursuant to this clause if the Company is at such time in breach of its
obligations under the Merger Agreement such as to cause a Material Adverse
Effect on the Company (as defined below); (ii) in connection with entering into
a definitive agreement in accordance with Section 6.8(b) of the Merger
Agreement, provided it has complied with all provisions of such section,
including the notice provisions therein, and that it makes simultaneous payment
of the Termination Fee plus any amounts then due as a reimbursement of expenses;
or (iii) if the Parent or the Offeror shall have made a material
misrepresentation or have breached in any material respect any of their
respective representations, covenants or other agreements contained in the
Merger Agreement, which breach (A) cannot be or has not been cured, in all
material respects, within 30 days after the giving of written notice to the
Parent or the Offeror, as applicable, and (B) limits or restricts the ability of
the Parent or the Offeror to consummate the transactions contemplated by the
Merger Agreement; or (d) by the Parent: (i) if prior to the purchase of Shares
pursuant to the Offer, the Company shall have breached any representation,
warranty, covenant or other agreement contained in the Merger Agreement which
(A) would give rise to the failure of a condition set forth in paragraph (e) or
(f) of Section 14--"Certain Conditions to the Offeror's Obligations" and (B)
cannot be or has not been cured, in all material respects, within 30 days after
the giving of written notice to the Company; or (ii) if any event set forth in
paragraph (d) of Section 14--"Certain Conditions to the Offeror's Obligations"
shall have occurred. "Material Adverse Effect on the Company" means any adverse
change, circumstance or effect that, individually or in the aggregate with all
other adverse changes, circumstances and effects, has had or will have a
material adverse effect on the business, financial condition, properties or
results of operations of the Company and its Subsidiaries taken as a whole,
other than any adverse change, circumstance or effect relating to or arising out
of (i) the economy or securities markets in general, (ii) the announcement of
the Merger Agreement or the transactions contemplated hereby (including any
impact on employees, vendors or customers resulting therefrom) or
 
                                       24
<PAGE>
(iii) the industry of the Company and its Subsidiaries in general, and not
specifically relating to the Company or its Subsidiaries.
 
    EFFECT OF TERMINATION; TERMINATION FEE.  The Merger Agreement provides that
in the event of the termination of the Merger Agreement, the Merger Agreement
shall forthwith become void and have no effect, without any liability on the
part of any party or its directors, officers or stockholders, other than the
provisions of Section 8.2, Section 8.3 and the last sentence of Section 6.2 of
the Merger Agreement which shall survive any such termination. Nothing contained
in Section 8.2 of the Merger Agreement shall relieve any party from liability
for any breach of the Merger Agreement or the Confidentiality Agreement.
 
    If (w) the Company terminates the Merger Agreement as provided in clause
(c)(ii) under TERMINATION above, (x) the Parent terminates the Merger Agreement
as provided in clause (d)(ii) under TERMINATION above, (y) either the Company or
the Parent terminates the Merger Agreement as provided in clause (b)(ii) under
TERMINATION above and (A) prior thereto there shall have been publicly announced
another Acquisition Proposal (provided, however, that solely for purposes of
this clause (A), the term Acquisition Proposal shall not include (1) the
purchase of less than 5% of any class or series of capital stock of the Company
if such purchase does not involve an offer to acquire additional shares of
capital stock of the Company that could cause any person, entity or "group" (as
defined in Section 13(d)(3) of the Exchange Act), other than the Offeror or its
affiliates or any group of which any of them is a member, to beneficially own 5%
or more of any such class or series or (2) any purchase of 5% or more of any
class or series of capital stock of the Company which can properly be reported
on a Schedule 13G of the Exchange Act and (B) an Acquisition Proposal pursuant
to which any person acquires all or a substantial part of the business or
properties of the Company or any of its Subsidiaries, any of the capital stock
(or securities exercisable for or convertible into such capital stock) of any of
the Subsidiaries of the Company or any capital stock (or securities exercisable
for or convertible into such capital stock) of the Company which represents 20%
or more of the equity interest or voting power of the Company shall be
consummated on or prior to March 31, 1999, or (z) the Parent terminates the
Merger Agreement as provided in clause (d)(i) under TERMINATION above and an
Acquisition Proposal pursuant to which any Person acquires all or a substantial
part of the business or properties of the Company or any of its Subsidiaries,
any of the capital stock (or securities exercisable for or convertible into such
capital stock) of any of the Subsidiaries of the Company or any capital stock
(or securities exercisable for or convertible into such capital stock) of the
Company which represents 20% or more of the equity interest or voting power of
the Company shall be consummated on or prior to March 31, 1999, then, the
Company is required to pay to the Offeror an amount equal to Seven Million Five
Hundred Thousand Dollars ($7,500,000)(the "Termination Fee"), plus an amount
equal to the Offeror's actual documented reasonable out-of-pocket fees and
expenses (including, without limitation, reasonable legal, investment banking,
financing commitment fees and commercial banking fees and expenses) incurred by
the Offeror and the Parent in connection with the due diligence investigation,
the Offer, the Merger, the Merger Agreement and the consummation of the
transactions contemplated by the Merger Agreement (the "Reimbursable Expenses").
The Company shall also be obligated to pay to the Offeror the Reimbursable
Expenses in such manner if the Parent shall terminate the Merger Agreement as
provided in clause (d)(i) under TERMINATION above (regardless of whether an
Acquisition Proposal is consummated thereafter). All such fees and expenses paid
constitute liquidated damages and the Company shall have no further liability to
the Offeror or the Parent under the Merger Agreement after the payment of such
fees and expenses, provided that nothing in this sentence shall affect any
liability the Company may have to the Offeror or Parent under the Purchase
Agreements (if any) and the Option Agreement.
 
    THE PURCHASE AGREEMENTS
 
    AGREEMENT TO TENDER.  The Offeror has entered into five Purchase Agreements,
each dated as of June 10, 1998, with the Stockholders identified therein (each a
"Stockholder") and collectively, the "Stockholders") beneficially owning an
aggregate of 536,960 Shares representing approximately 15.3% of the outstanding
Shares on a fully diluted basis (the "Stockholders' Shares") pursuant to which
the
 
                                       25
<PAGE>
Stockholders have agreed to tender into the Offer all of the Stockholders'
Shares and not withdraw any of the Stockholders' Shares unless an election is
made by the Offeror to purchase the Stockholders' Shares. Each Stockholder
severally has agreed to deliver to the Depositary, immediately following the
date of this Offer to Purchase, the Letter of Transmittal together with the
certificates for the Stockholder's Shares, if available, or a "Notice of
Guaranteed Delivery," if the Stockholder's Shares are not available. Each of the
Stockholders has also severally agreed not to withdraw any Shares tendered into
the Offer unless the Offer is terminated by the Parent or the Offeror without
any Shares being purchased thereunder.
 
    OPTION TO PURCHASE.  Pursuant to the Purchase Agreements, each Stockholder
has also severally granted to the Offeror a conditional irrevocable option (the
"Stock Option") to purchase all of such Stockholder's Shares legally and/or
beneficially owned by such Stockholder at a purchase price equal to $73.50 per
Share. The Stock Option may be exercised by the Offeror, in whole and for all of
such Stockholder's Shares but not in part or for less than all of such
Stockholder's Shares (i) if the Offer was terminated by the Offeror for the
reasons set forth in paragraph (d) of Section 14--"Certain Conditions to the
Offeror's Obligations" or (ii) in the case of the expiration of the Offer, if
the Offer expires without the purchase of Shares thereunder and either without
satisfaction of the Minimum Condition or after the occurrence of circumstances
giving rise to a right of termination by the Offeror for the reasons set forth
in paragraph (d) of Section 14--"Certain Conditions to the Offeror's
Obligations", in each case without any violation of the Offer or the Merger
Agreement by the Parent or the Offeror. Notice of exercise may be given at any
time during the period (the "Exercise Period") commencing on the date on which
the Offer is terminated or expires (as described above) and ending on March 31,
1999. In addition, the Offeror may also exercise the Stock Option if the Company
terminates the Merger Agreement as provided in clause (c)(ii) under THE MERGER
AGREEMENT--TERMINATION above, whereupon the Exercise Period shall commence on
the date such termination rights are exercised and end on March 31, 1999.
 
    CONDITIONS TO DELIVERY OF THE SHARES.  The Purchase Agreements provides that
the obligation of each Stockholder to deliver such Stockholder's Shares upon
exercise of the Stock Option is subject to (i) all waiting periods under the HSR
Act applicable to the exercise of the Stock Option having expired or been
terminated, (ii) there being no permanent injunction or other order by any court
of competent jurisdiction restricting, preventing or prohibiting the exercise of
the Stock Option or the delivery of the Stockholder's Shares in respect of such
exercise.
 
    REPRESENTATION AND WARRANTIES.  The Purchase Agreements contain customary
representations and warranties by each Stockholder, including those relating to
(i) authority to enter into the Purchase Agreements and sell Shares owned by
such Stockholder, (ii) good and marketable title to such Stockholder's Shares,
free and clear of all liens, claims, encumbrances and security interests, (iii)
legality, validity and binding effect of the Purchase Agreements, and (iv) no
violation of agreements, judgments, laws, rules and regulations. The Purchase
Agreements also contain customary representations and warranties by the Offeror,
including those relating to authority to enter into the Purchase Agreements, the
legality, validity and binding effect of the Purchase Agreements and no
violation of agreements, judgments, laws, rules and regulations.
 
    NO DISPOSITION OF STOCKHOLDERS' SHARES AND NO ACQUISITION OF
SHARES.  Pursuant to the Purchase Agreements, each Stockholder severally agreed
that, except as contemplated by the Purchase Agreements, such Stockholder will
not offer or agree to, sell, transfer, assign or otherwise dispose of, or create
any option, restriction, right of first refusal agreement or limitation on such
Stockholder's voting rights with respect to, such Stockholder's Shares.
 
    NO SOLICITATION.  Pursuant to the Purchase Agreements, each Stockholder and
his affiliates have agreed not to directly or indirectly, encourage, solicit,
participate in or initiate discussions or negotiations with, or provide any
information to, any corporation, partnership, person or other entity or group
(other than Offeror or any of its affiliates or representatives) concerning any
proposal or offer to acquire all or a substantial part of the business or
properties of the Company or any of its subsidiaries, whether by merger,
 
                                       26
<PAGE>
tender offer, exchange offer, sale of assets or similar transaction involving
the Company or any subsidiary, division or operating or principal business unit
of the Company, except that this covenant shall not restrict the Stockholder's
ability to act in such Stockholder's capacity as a director of the Company in
accordance with Section 6.8 of the Merger Agreement. The Purchase Agreements
also provide that each Stockholder shall immediately cease and cause to be
terminated any existing activities, discussions or negotiations by such
Stockholder or his affiliates or any investment banker, attorney, accountant or
other advisor or representative of such Stockholder or his affiliates with
parties conducted prior to the date of the Purchase Agreements with respect to
any of the foregoing.
 
    VOTING AGREEMENT.  During the time the Purchase Agreements are in effect,
each Stockholder has agreed to vote all such Stockholder's Shares (i) in favor
of the Merger, the Merger Agreement and the transactions contemplated by the
Merger Agreement, (ii) against any action or agreement that would result in a
breach in any material respect of any covenant, representation or warranty or
any other obligation of the Company under the Merger Agreement, and (iii)
against any action or agreement that would materially impede, interfere with or
attempt to discourage the Offer or the Merger, including, but not limited to:
(i) any extraordinary corporate transaction (other than the Merger), such as a
merger, reorganization, recapitalization or liquidation involving the Company or
any of its Subsidiaries or any proposal made in opposition to or in competition
with the Merger; (ii) a sale or transfer of a material amount of assets of the
Company or any of its Subsidiaries; (iii) and change in the management or board
of directors of the Company, except as otherwise agreed to in writing by Offeror
or the Parent; (iv) any material change in the present capitalization or
dividend policy of the Company; or (v) any other material change in the
corporate structure or business of the Company or any of its Subsidiaries.
 
    In the event any Stockholder shall fail to comply with the provisions of
Section 6.1 of the Purchase Agreements as determined by the Offeror in its sole
discretion, such failure shall result, without any further action by such
Stockholder, in the irrevocable appointment of the Offeror as the attorney and
proxy of such Stockholder, with full power of substitution, to vote, and
otherwise act (by written consent or otherwise) with respect to all of the
Shares that such Stockholder is entitled to vote at any meeting of stockholders
of the Company (whether annual or special and whether or not an adjourned or
postponed meeting) or consent in lieu of any such meeting or otherwise, on the
matters and in the manner specified in Section 6.1 of the Purchase Agreements.
Each Stockholder revokes, effective upon the execution and delivery of the
Merger Agreement by the parties thereto, all other proxies and powers of
attorney with respect to the Shares that such Stockholder may have appointed or
granted prior to the date of the Purchase Agreements, and no subsequent proxy or
power of attorney (except in furtherance of Stockholder's obligations under
Section 6.1 of the Purchase Agreements shall be given or written consent
executed (and if given or executed, shall not be effective) by the Stockholder
with respect thereto so long as the Purchase Agreements remain in effect.
 
    TERMINATION.  The Purchase Agreements will terminate, without any action by
any of the parties, on the date on which the Merger Agreement terminates in
accordance with its terms, except with respect to the exercise of the Stock
Option. The Stock Option may be exercised after termination of the Merger
Agreement on the terms described above under "Option to Purchase."
 
    THE GUARANTEE.  In connection with each Purchase Agreement, the Parent has
guaranteed the performance of the obligations undertaken by the Offeror therein.
 
    THE OPTION AGREEMENT
 
    GRANT OF OPTION.  Pursuant to the Option Agreement dated June 10, 1998 (the
"Option Agreement") among the Company and the Parent, the Company granted to the
Parent an irrevocable option (the "Company Option") to purchase up to 698,540
shares of Common Stock ("Option Shares"), representing 19.9% of the issued and
outstanding shares of Common Stock on the date of the Option Agreement, at a
price per share of $73.50 ("Option Price") payable in cash.
 
                                       27
<PAGE>
    EXERCISE OF THE COMPANY OPTION.  The Option Agreement provides that: (a) The
Company Option may be exercised, in whole or in part, at any time and from time
to time after any Triggering Event (as defined below) shall have occurred and
prior to the expiration thereof, provided that (i) all waiting periods under the
HSR Act required for the purchase of the Option Shares shall have expired or
been waived, (ii) no breach by the Parent or the Offeror shall have occurred and
be continuing under the Option Agreement or the Merger Agreement and (iii) there
shall not be in effect any preliminary or final injunction or other order issued
by any court or governmental, administrative or regulatory agency or authority,
prohibiting the issuance of the Option Shares pursuant to the Option Agreement.
The Company Option shall expire upon the earlier of (i) the date of consummation
of the Merger, (ii) twenty (20) days after the date of consummation of any
Superior Proposal or Acquisition Proposal (as such terms as defined in the
Merger Agreement) under circumstances which obligate the Company to pay the
Termination Fee, or (iii) the date upon which the Merger Agreement is terminated
other than in connection with the occurrence of a Triggering Event; and (b) if
the Parent wishes to exercise the Company Option for all or some of the Option
Shares, the Parent shall send a written notice (the "Notice") to the Company
specifying the number of Option Shares it will purchase pursuant to such
exercise and the place and date not less than three (3) nor more than twenty
(20) days from the date of the Notice for the closing of such purchase.
 
    TRIGGERING EVENT.  Under the Option Agreement, a "Triggering Event" shall
mean the occurrence of an event which requires the payment of the Termination
Fee.
 
    COVENANTS.  The Option Agreement provides that: (a) upon the request of the
Parent, the Company agrees to file a registration statement and use its best
efforts to cause such registration statement to become effective under the
Securities Act and any applicable state securities laws with respect to any
proposed disposition by the Parent of the Option Shares, or any portion thereof,
unless, in the written opinion of counsel to the Company, addressed to the
Parent, registration is not required for the proposed disposition of such Option
Shares; PROVIDED, HOWEVER, that the Company shall not be obligated to file more
than one registration statement (under federal and, if applicable, state law)
with respect to the Option Shares. The registration effected in accordance with
the foregoing shall be effected at the Company's expense.
 
    (b) Upon the request of the Parent, the Company agrees that it will promptly
file applications to list any Option Shares, whether issued or unissued, on the
NASDAQ National Market System and will use its best efforts to obtain approval
of such listing.
 
    (c) Upon the request of the Parent prior to the Parent's exercise of the
Company Option, the Company shall use its reasonable best efforts to file as
soon as practicable notifications under the HSR Act with respect to the
Offeror's exercise of the Company Option and to respond as promptly as
practicable to any inquiries received from the Federal Trade Commission and the
Antitrust Division of the Department of Justice for additional information or
documentation and to respond as promptly as practicable to all inquiries and
requests received from any State Attorney General or other Governmental Entity
in connection with antitrust matters. Each of the Company and the Parent shall
further take all reasonable actions necessary to file any other forms or
notifications which may be required by any foreign Governmental Entity and to
obtain any approvals which may be required in connection therewith.
 
    REPRESENTATIONS AND WARRANTIES OF THE COMPANY.  The Option Agreement
contains customary representations and warranties by the Company including those
relating to: (i) authority to enter into the Option Agreement and perform all of
its obligations under the Option Agreement; (ii) required consents; (iii) due
authorization of the Option Shares; and (iv) no violation of agreements,
judgments, rules and regulations. The Option Agreement also contains customary
representations and warranties by the Parent including those related to
authority to enter into the Option Agreement.
 
                                       28
<PAGE>
    REPRESENTATIONS AND WARRANTIES TO SURVIVE DELIVERY.  Pursuant to the Option
Agreement, all representations and warranties contained in the Option Agreement,
or contained in certificates of officers of the Company submitted pursuant to
the Option Agreement, survive delivery of and payment for the Option Shares for
a period expiring on the earlier of (a) the first anniversary of the date of
delivery and payment for the Option Shares and (b) the date upon which the
Parent shall have sold or otherwise disposed of all of the Option Shares (other
than to a direct or indirect majority owned subsidiary of the Parent).
 
WKUS LETTER
 
    GENERAL.  Pursuant to the WKUS Letter, WKUS agreed to fund the obligations
of the Parent and the Offeror, through available cash balances and existing bank
credit lines of Wolters Kluwer. WKUS further represented and warranted that
there are available cash balances and existing bank credit lines which will
enable WKUS to meet this obligation.
 
14. CERTAIN CONDITIONS TO THE OFFEROR'S OBLIGATIONS.
 
    Notwithstanding any other term of the Offer, and in addition to (and not in
limitation of) Offeror's rights to extend and amend the Offer at any time in its
sole discretion (subject to the provisions of the Merger Agreement) the Offeror
shall not be required to accept for payment or, subject to any applicable rules
and regulations of the Commission, including Rule 14e-l(c) under the Exchange
Act (relating to the Offeror's obligation to pay for or return tendered Shares
after the termination or withdrawal of the Offer), pay for, and may delay the
acceptance for payment of or, subject to the restriction referred to above, the
payment for, any tendered Shares, and may terminate or amend the Offer as to any
Shares not then paid for, if (i) any applicable waiting period under the HSR Act
has not expired or terminated, (ii) the Minimum Condition has not been
satisfied, or (iii) at any time on or after the date of the Merger Agreement and
before the time of acceptance for payment for any such Shares, any of the
following events shall have occurred:
 
    (a) there shall be any statute, rule, regulation, judgment, order or
injunction promulgated, entered, enforced, enacted, issued or deemed applicable,
pursuant to an authoritative interpretation by or on behalf of a Government
Entity, to the Offer or the Merger or any other action shall be taken by any
Government Entity, other than the application to the Offer or the Merger of any
applicable waiting periods under the HSR Act (i) seeking to prohibit or impose
any material limitations on the Offeror's or the Parent's ownership or operation
(or that of any of their respective Subsidiaries or affiliates) of all or a
material portion of their or the Company's businesses or assets (or that of any
of its Subsidiaries), or to compel the Offeror or the Parent or their respective
Subsidiaries and affiliates to dispose of or hold separate any material portion
of the business or assets of the Company or the Parent and their respective
Subsidiaries, in each case taken as a whole, (ii) challenging the acquisition by
the Offeror or the Parent of any Shares under the Offer, seeking to restrain or
prohibit the making or consummation of the Offer or the Merger or the
performance of any of the other transactions contemplated by the Agreement or
the Purchase Agreements, or seeking to obtain from the Company, the Offeror or
the Parent any damages that are material in relation to the Company and its
Subsidiaries taken as a whole, (iii) seeking to impose material limitations on
the ability of the Offeror, or render the Offeror unable, to accept for payment,
pay for or purchase some or all of the Shares pursuant to the Offer and the
Merger or (iv) seeking to impose material limitations on the ability of the
Offeror or the Parent effectively to exercise full rights of ownership of the
Shares, including, without limitation, the right to vote the Shares purchased by
it on all matters properly presented to the Company's stockholders or there
shall be pending any suit, action or proceeding by any Governmental Entity
against the Offeror, the Parent, the Company or any Subsidiary of the Company
which is reasonably likely to have a Material Adverse Effect on the Company;
 
    (b) there shall be threatened, instituted or pending any action, suit, or
proceeding by any Governmental Entity against the Offeror, the Parent, the
Company or any Subsidiary of the Company, that is
 
                                       29
<PAGE>
reasonably likely, directly or indirectly, to result in any of the consequences
referred to in clauses (i) through (iv) of paragraph (a) above;
 
    (c) there shall have occurred any events after the date of the Merger
Agreement which have or will have a Material Adverse Effect on the Company;
 
    (d) (i) the Board of Directors of the Company or any committee thereof shall
have withdrawn or modified in a manner adverse to the Parent or the Offeror its
approval or recommendation of the Offer, the Merger or the Merger Agreement, or
approved or recommended any Acquisition Proposal or (ii) the Company shall have
entered into any agreement with respect to any Superior Proposal in accordance
with the Merger Agreement;
 
    (e) the representations and warranties of the Company set forth in the
Merger Agreement shall not be true and correct, in each case (i) as of the date
referred to in any representation or warranty which addresses matters as of a
particular date, or (ii) as to all other representations and warranties, as of
the date of the Merger Agreement and as of the scheduled expiration of the Offer
unless the inaccuracies without giving effect to any materiality or material
adverse effect qualifications or materiality exceptions contained therein under
such representations and warranties, taking all the inaccuracies under all such
representations and warranties together in their entirety, do not result in
Material Adverse Effect on the Company;
 
    (f) the Company shall have failed to perform any obligation or to comply
with any agreement or covenant to be performed or complied with by it (i) under
Section 6.1 or 6.8 of the Merger Agreement or (ii) under any other agreement or
covenant to be performed or complied with by it under the Merger Agreement,
unless the failure to so perform or comply would not have a Material Adverse
Effect on the Company; or
 
    (g) the Merger Agreement shall have been terminated in accordance with its
terms.
 
    The foregoing conditions are for the benefit of the Parent and the Offeror,
may be asserted by Parent or the Offeror regardless of the circumstances giving
rise to any such conditions and may be waived by Parent or the Offeror in whole
or in part at any time and from time to time in their reasonable discretion, in
each case, subject to the terms of the Merger Agreement. The failure by the
Parent or the Offeror at any time to exercise any of the foregoing rights shall
not be deemed a waiver of any such right and each such right shall be deemed an
ongoing right which may be asserted at any time and from time to time.
 
15. CERTAIN LEGAL MATTERS.
 
    Except as set forth in this Section, the Offeror is not aware of any
approval or other action by any governmental or administrative agency which
would be required for the acquisition or ownership of Shares by the Offeror as
contemplated herein. Should any such approval or other action be required, it
will be sought, but the Offeror has no current intention to delay the purchase
of Shares tendered pursuant to the Offer pending the outcome of any such matter,
subject, however, to the Offeror's right to decline to purchase Shares if any of
the conditions specified in Section 14--"Certain Conditions to the Offeror's
Obligations" shall have occurred. There can be no assurance that any such
approval or other action, if needed, would be obtained or would be obtained
without substantial conditions, or that adverse consequences might not result to
the Company's business or that certain parts of the Company's business might not
have to be disposed of if any such approvals were not obtained or other action
taken.
 
    U.S. ANTITRUST.  Under the provisions of the HSR Act applicable to the
Offer, the acquisition of Shares under the Offer may be consummated following
the expiration of a 15-day waiting period following the filing by Wolters Kluwer
and the Company of a Premerger Notification and Report Form with respect to the
Offer, unless the Parent receives a request for additional information or
documentary material from the Antitrust Division or the FTC or unless early
termination of the waiting period is granted. Wolters Kluwer, the ultimate
parent entity of the Parent and the Offeror expects to make such a filing on
June 17,
 
                                       30
<PAGE>
1998 and, accordingly, the initial waiting period will expire on July 2, 1998.
If, within the initial 15-day waiting period, either the Antitrust Division or
the FTC requests additional information or documentary material concerning the
Offer, the waiting period will be extended through the tenth day after the date
of substantial compliance by all parties receiving such requests. Complying with
a request for additional information or documentary material can take a
significant amount of time.
 
    The Antitrust Division and the FTC frequently scrutinize the legality under
the antitrust laws of transactions such as the Offeror's proposed acquisition of
the Company. At any time before or after the Offeror's acquisition of Shares
pursuant to the Offer, the Antitrust Division or the FTC could take such action
under the antitrust laws as either deems necessary or desirable in the public
interest, including seeking to enjoin the purchase of Shares pursuant to the
Offer or the consummation of the Merger, or seeking the divestiture of Shares
acquired by the Offeror or the divestiture of substantial assets of the Company
or its Subsidiaries or the Parent or its Subsidiaries. Private parties may also
bring legal action under the antitrust laws under certain circumstances. There
can be no assurance that a challenge to the Offer or to the consummation of the
Merger on antitrust grounds will not be made, or, if such a challenge is made,
of the result thereof.
 
    If any applicable waiting period under the HSR Act has not expired or been
terminated prior to the Expiration Date, the Offeror will not be obligated to
proceed with the Offer or the purchase of any Shares not theretofore purchased
pursuant to the Offer. See Section 14--"Certain Conditions to the Offeror's
Obligations".
 
    APPRAISAL RIGHTS.  No appraisal rights are available in connection with the
Offer. However, if the Merger is consummated, stockholders of the Company would
have certain rights under the Delaware GCL to dissent and demand appraisal of,
and payment in cash of the fair value of, their Shares. Such rights, if the
statutory procedures are complied with, could lead to a judicial determination
of the fair value (excluding any element of value arising from the
accomplishment or expectation of the Merger) required to be paid in cash to such
dissenting holders for their Shares. Any such judicial determination of the fair
value of Shares could be based upon considerations other than or in addition to
the price paid in the Offer and the market value of the Shares, including asset
values and the investment value of the Shares. The value so determined could be
more or less than the purchase price per Share pursuant to the Offer or the
consideration per Share to be paid in the Merger.
 
    DELAWARE STATE TAKEOVER LAWS.  Under the Delaware GCL, if the Offeror
acquires less than 90% of each class of the understanding Shares, the Merger
would require, among other things, the affirmative vote of the holders of at
least a majority of all the outstanding Shares. If the Offeror acquires,
pursuant to the Offer or otherwise, including pursuant to the Purchase
Agreements, voting power with respect to at least a majority of the outstanding
Shares which would be the case if the Minimum Condition is satisfied, will have
the voting power to effect the merger without the vote of any other stockholder,
which it intends to do. The Delaware GCL also provides that if a parent company
owns at least 90% of each class of stock of a subsidiary, the parent company can
effect a merger with the subsidiary without the authorization of the other
stockholders of the subsidiary. Accordingly, if the Offeror acquires 90% or more
of the outstanding Shares pursuant to the Offer and the Purchase Agreements or
otherwise, the Offeror could, and intends to, consummate the Merger without the
approval of any other stockholders of the Company.
 
    In addition, several decisions by Delaware courts have held that, in certain
instances, a controlling stockholder of a corporation involved in a merger has a
fiduciary duty to the other stockholders that requires the merger to be fair to
such other stockholders. In determining whether a merger is fair to minority
stockholders, the Delaware courts have considered, among other things, the type
and amount of consideration to be received by the stockholders and whether there
were fair dealings among the parties. The Delaware Supreme Court has indicated
in recent decisions that in most cases the remedy available in a merger that is
found not to be "fair" to minority stockholders is the right to appraisal
described above or a damages remedy based on essentially the same principles.
 
                                       31
<PAGE>
    Section 203 of the Delaware GCL prohibits business combination transactions
involving a Delaware corporation and an "interested stockholder" (defined
generally as any person that directly or indirectly beneficially owns 15% or
more of the outstanding voting stock of the subject corporation) for three years
following the date such person became an "interested stockholder," unless
certain exceptions apply, including that prior to such date the Board of
Directors of the Company approved either the business combination or the
transaction which resulted in such person being an interested stockholder. As
set forth below, the Company's Board of Directors has taken actions to make
Delaware GCL Section 203 inapplicable to the Parent and the Offeror in
connection with the Offer, the Merger, the Purchase Agreements, the Option
Agreement and the transactions contemplated by the Option Agreement.
 
    In the Merger Agreement, the Company represented that its Board of Directors
has unanimously approved the Merger Agreement, the Purchase Agreements and the
Option Agreement and the transactions contemplated thereby, including the Offer
and the Merger, for purposes of Delaware GCL Section 203, such approval
occurring prior to the time the Offeror became an "interested stockholder" as
defined in Delaware GCL Section 203, so that the provisions thereof are not
applicable to such transactions.
 
    OTHER STATE TAKEOVER LAWS.  A number of other states have adopted laws and
regulations applicable to attempts to acquire securities of corporations which
are incorporated, or have substantial assets, stockholders, principal executive
offices or principal places of business, or whose business operations otherwise
have substantial economic effects in such states. In EDGAR V. MITE CORP., in
l982, the Supreme Court of the United States (the "U.S. Supreme Court")
invalidated on constitutional grounds the Illinois Business Takeover statute,
which, as a matter of state securities law, made takeovers of corporations
meeting certain requirements more difficult. However, in 1987, in CTS CORP. V.
DYNAMICS CORP. OF AMERICA, the U.S. Supreme Court held that the State of Indiana
may, as a matter of corporate law and, in particular, with respect to those
aspects of corporate law concerning corporate governance, constitutionally
disqualify a potential acquirer from voting on the affairs of a target
corporation without the prior approval of the remaining stockholders. The state
law before the U.S. Supreme Court was by its terms applicable only to
corporations that had a substantial number of stockholders in the state and were
incorporated there.
 
    The Company, directly or through subsidiaries, conducts business in a number
of states throughout the United States, some of which have enacted takeover
laws. The Offeror does not know whether any of these laws will, by their terms,
apply to the Offer or the Merger and has not complied with any such laws. Should
any person seek to apply any state takeover law, the Offeror will take such
action as then appears desirable, which may include challenging the validity or
applicability of any such statute in appropriate court proceedings. In the event
it is asserted that one or more state takeover laws is applicable to the Offer
or the Merger, and an appropriate court does not determine that it is
inapplicable or invalid as applied to the Offer, the Offeror might be required
to file certain information with, or receive approvals from, the relevant state
authorities. In addition, if enjoined, the Offeror might be unable to accept for
payment any Shares tendered pursuant to the Offer, or be delayed in continuing
or consummating the Offer and the Merger. In such case, the Offeror may not be
obligated to accept for payment any Shares tendered. See Section 14--"Certain
Conditions to the Offeror's Obligations."
 
16. FEES AND EXPENSES.
 
    Neither the Offeror nor the Parent, nor any officer, director, stockholder,
agent or other representative of the Offeror or the Parent, will pay any fees or
commissions to any broker, dealer or other person (other than the Dealer Manager
and the Information Agent) for soliciting tenders of Shares pursuant to the
Offer. Brokers, dealers, commercial banks and trust companies and other nominees
will, upon request, be reimbursed by the Offeror for customary mailing and
handling expenses incurred by them in forwarding materials to their customers.
 
    Credit Suisse First Boston Corporation ("Credit Suisse First Boston" or
"CSFB") is acting as the Dealer Manager in connection with the Offer and as
financial advisor to Wolters Kluwer in connection
 
                                       32
<PAGE>
with the Parent's proposed acquisition of the Company, for which services CSFB
will receive customary compensation. Wolters Kluwer also has agreed to reimburse
CSFB for its out-of-pocket expenses, including the fees and expenses of legal
counsel and other advisors, incurred in connection with its engagement, and to
indemnify CSFB and certain related persons against certain liabilities and
expenses in connection with its engagement, including certain liabilities under
the federal securities laws. In the ordinary course of business, CSFB and its
affiliates may actively trade the debt and equity securities of Wolters Kluwer
and the equity securities of the Company for their own account and for the
accounts of customers and, accordingly, may at any time hold a long or short
position in such securities.
 
    The Offeror has retained Georgeson & Company Inc., as Information Agent, and
Morgan Guaranty Trust Company of New York, as Depositary, in connection with the
Offer. The Information Agent and the Depositary will receive reasonable and
customary compensation for their services hereunder and reimbursement for their
reasonable out-of-pocket expenses. The Information Agent and the Depositary will
also be indemnified by the Offeror against certain liabilities in connection
with the Offer. The Information Agent may contact holders of Shares by mail,
telex, telegraph and personal interviews and may request brokers, dealers and
other nominee stockholders to forward materials relating to the Offer to
beneficial owners of Shares.
 
17. MISCELLANEOUS.
 
    The Offer is not being made to, nor will tenders be accepted from or on
behalf of, holders of Shares residing in any jurisdiction in which the making or
acceptance thereof would not be in compliance with the securities, blue sky or
other laws of such jurisdiction. In any jurisdiction where the securities, blue
sky or other laws require the Offer to be made by a licensed broker or dealer,
the Offer shall be deemed to be made on behalf of the Offeror by the Dealer
Manager or one or more registered brokers or dealers licensed under the laws of
such jurisdiction.
 
    NO PERSON HAS BEEN AUTHORIZED TO GIVE ANY INFORMATION OR MAKE ANY
REPRESENTATION ON BEHALF OF THE OFFEROR OTHER THAN AS CONTAINED IN THIS OFFER TO
PURCHASE OR IN THE LETTER OF TRANSMITTAL AND, IF ANY SUCH INFORMATION OR
REPRESENTATION IS GIVEN OR MADE, IT SHOULD NOT BE RELIED UPON AS HAVING BEEN
AUTHORIZED.
 
    The Offeror and the Parent have filed with the Commission (i) a Schedule
14D-l, pursuant to Section 14(d)(1) of the Exchange Act and Rule 14d-3
promulgated thereunder, furnishing certain information with respect to the Offer
and (ii) a Schedule 13D, pursuant to Section 13(d)(1) of the Exchange Act. Such
Schedule 14D-l and Schedule 13D, and any amendments thereto, including exhibits,
may be examined and copies may be obtained at the same places and in the same
manner as set forth with respect to the Company in Section 8--"Certain
Information Concerning the Company" (except that they will not be available at
the regional offices of the Commission).
 
                                                           PPC ACQUISITION CORP.
 
June 16, 1998
 
                                       33
<PAGE>
                                                                      SCHEDULE I
 
                        DIRECTORS AND EXECUTIVE OFFICERS
                                       OF
              WOLTERS KLUWER, WOLTERS KLUWER INTERNATIONAL, WKUS,
                     WK AMERICA, THE PARENT AND THE OFFEROR
 
    1. MEMBERS OF THE SUPERVISORY BOARD AND EXECUTIVE BOARD AND EXECUTIVE
OFFICERS OF WOLTERS KLUWER.  The following table sets forth the name, business
address and present principal occupation or employment and material occupations,
positions, offices or employments for the past five years of each member of the
Supervisory Board and Executive Board and each Executive Officer of Wolters
Kluwer. Each such person is a citizen of the Netherlands.
 
SUPERVISORY BOARD
 
<TABLE>
<CAPTION>
                                                                          INDIVIDUAL PRINCIPAL OCCUPATION OR
NAME AND BUSINESS ADDRESS                       OFFICE                        EMPLOYMENT (PRESENT/PAST)
- ---------------------------------  ---------------------------------  ------------------------------------------
<S>                                <C>                                <C>
 
O. Hattink.......................  Chairman, Member since 1981        Chairman of Supervisory Board of Aon
  Landgoed Backershagen 33                                            Holdings BV and RBC Finance BV
  2243 AX WASSENAAR                                                   Vice-chairman of Supervisory Board of IHC
                                                                      Caland NV and Member of Supervisory Board
                                                                      of Coca Cola Beverages Nederland BV
                                                                      Director British Gas
                                                                      International Holdings BV
                                                                      Advisory Director Invesco
                                                                      Europe Limited
                                                                      Chairman, Committee of Shareholders
                                                                      Koninklijke Ten Cate NV
 
B.H. ter Kuile...................  Member since 1986                  Emeritus Prof. European Law, Erasmus
  Neuhuyskade 4                                                       University of Rotterdam
  2596 XL DEN HAAG                                                    Member and secretary of Supervisory Board
                                                                      of NV Verenigd Streekvervoer Nederland
                                                                      Deputy-Justice Court of Justice of The
                                                                      Hague
 
J.M.M. Maeijer...................  Member since 1982                  Emeritus Prof. Commercial Law University
  Pauluslaan 17                                                       of Nijmegen
  6564 AP HEILIG                                                      Member of Supervisory Board of Vendex
  LANDSTICHTING                                                       International NV
                                                                      Deputy-Justice Court of Justice of Den
                                                                      Bosch
 
J.V.H. Pennings..................  Member since 1995                  Chairman of the Executive Board of Oce NV
  Casinoweg 170                                                       Chairman of Supervisory Board of
  5915 ER VENLO                                                       Koninklijke Grolsch NV and Koninklijke IBC
                                                                      Member of Supervisory Board of De
                                                                      Nederlandsche Bank NV and Tulip
                                                                      Computers
</TABLE>
 
                                      I-1
<PAGE>
<TABLE>
<CAPTION>
                                                                          INDIVIDUAL PRINCIPAL OCCUPATION OR
NAME AND BUSINESS ADDRESS                       OFFICE                        EMPLOYMENT (PRESENT/PAST)
- ---------------------------------  ---------------------------------  ------------------------------------------
<S>                                <C>                                <C>
H. de Ruiter.....................  Member since 1994                  Chairman of Supervisory Board of
  Prins Frederiklaan 16                                               Koninklijke Ahold NV, Beers NV,
  2243 HW WASSENAAR                                                   Koninklijke Hoogovens NV and Koninklijke
                                                                      Pakhoed NV
                                                                      Vice-chairman of Supervisory Board of
                                                                      AEGON NV and Member of Supervisory Board
                                                                      of Heineken NV and NV Koninklijke
                                                                      Nederlandse Petroleum Maatschappij
 
A.H.C.M. Walravens...............  Member since 1978                  Professor and consultant
  Oude Delft 130                                                      Chairman of Supervisory Board of
  2611 CG DELFT                                                       Tauw Beheer and NV Verenigd Streekvervoer
                                                                      Nederland
                                                                      Member of Supervisory Board of Achmea
                                                                      Holding, Bull Benelux and CSM
                                                                      Member Monitoring Committee Deloitte &
                                                                      Touche
 
N.J. Westdijk....................  Member since 1993                  Chairman Executive Board of Royal Pakhoed
  Nieuwe Gracht 161                                                   NV
  3512 LL UTRECHT                                                     Member of Supervisory Board of De
                                                                      Nationale Investeringsbank NV and Fortis
                                                                      AMEV NV
</TABLE>
 
EXECUTIVE BOARD
 
    The names of the members of the Executive Board of Wolters Kluwer, whose
present principal occupations are serving as such members and whose present
business address is, unless otherwise indicated, c/o Wolters Kluwer,
Stadhouderskade 1, 1000 AV Amsterdam, the Netherlands.
 
<TABLE>
<CAPTION>
NAME AND BUSINESS ADDRESS                                            OFFICE
- ------------------------------  ---------------------------------------------------------------------------------
 
<S>                             <C>
C.J. Brakel...................  Chairman since 1995; Member since 1981.
 
C.H. van Kempen...............  Member since 1993; Chief Executive Officer of Wolters Kluwer Italy, an indirect
                                wholly owned subsidiary of Wolters Kluwer, from 1990 through 1993.
 
Robert Pieterse...............  Member since 1987.
 
Peter W. van Wel..............  Member since 1993; President and Chief Executive Officer of WKUS, from 1990
                                through 1993, and from 1996 to the present.
</TABLE>
 
                                      I-2
<PAGE>
EXECUTIVE OFFICERS
 
    The names of the Executive Officers of Wolters Kluwer, whose present
principal occupations are serving as such officers, are:
 
<TABLE>
<CAPTION>
NAME AND BUSINESS ADDRESS                                            OFFICE
- ------------------------------  ---------------------------------------------------------------------------------
 
<S>                             <C>
Hans E.M. van Dinter..........  Chief Financial Officer for more than the past five years.
 
A.S.F. Kuipers................  Director of Business Development since January 1995; prior to 1995,
                                Managing Director of BBI Publishers.
 
Marcel L. Mock................  Head of the Legal Department and Secretary to the Executive Board since June 1997
                                and November 1997, respectively. Prior to 1997, European Legal Officer and
                                Statutory Director of Hunter Douglas Europe B.V.
 
M.H. Sanders..................  Director of Personnel & Organization for more than five years.
</TABLE>
 
    2. MEMBERS OF THE EXECUTIVE BOARD OF WOLTERS KLUWER INTERNATIONAL.  The
following table sets forth the name, business address and present principal
occupation or employment and material occupations, positions, offices or
employments for the past five years of each member of the Executive Board of
Wolters Kluwer International. Each such person is a citizen of the Netherlands,
and the business address of each such person is c/o Wolters Kluwer,
Stadhouderskade 1, 1000 AV Amsterdam, the Netherlands.
 
<TABLE>
<CAPTION>
                                                                          INDIVIDUAL PRINCIPAL OCCUPATION OR
NAME AND BUSINESS ADDRESS                       OFFICE                        EMPLOYMENT (PRESENT/PAST)
- ---------------------------------  ---------------------------------  ------------------------------------------
<S>                                <C>                                <C>
Hans E.M. van Dinter.............  Member                             Chief Financial Officer of Wolters Kluwer
                                                                      for more than the past five years.
 
Marcel L. Mock...................  Member                             Head of the Legal Department and Secretary
                                                                      to the Executive Board of Wolters Kluwer
                                                                      since June 1997 and November 1997,
                                                                      respectively. Prior to 1997, European
                                                                      Legal Officer and Statutory Director of
                                                                      Hunter Douglas Europe B.V.
</TABLE>
 
    3. DIRECTORS AND EXECUTIVE OFFICERS OF WKUS. The following table sets forth
the name, business address and present principal occupation or employment and
material occupations, positions, offices or employments for the past five years
of each Director and Executive Officer of WKUS. Unless otherwise indicated, each
such person is a citizen of the Netherlands, each occupation set forth opposite
an individual's name refers to employment with WKUS and the business address of
each such person is c/o Wolters Kluwer, Stadhouderskade 1, 1000 AV Amsterdam,
the Netherlands.
 
<TABLE>
<CAPTION>
                                                                          INDIVIDUAL PRINCIPAL OCCUPATION OR
NAME AND BUSINESS ADDRESS                       OFFICE                        EMPLOYMENT (PRESENT/PAST)
- ---------------------------------  ---------------------------------  ------------------------------------------
<S>                                <C>                                <C>
 
Peter W. van Wel.................  Chairman of the Board from 1994    Member of the Executive Board of Wolters
  c/o Wolters Kluwer               to the present, President and      Kluwer since 1993; President and Chief
  United States Inc.               Chief Executive Officer from 1990  Executive Officer of WKUS from 1990 to
  161 North Clark Street           to 1993 and from 1996 to the       1993 and 1996 to the present.
  48th Floor                       present
  Chicago, IL 60601
 
C.J. Brakel......................  Director                           Chairman of the Executive Board of Wolters
                                                                      Kluwer since 1995; member since 1981.
</TABLE>
 
                                      I-3
<PAGE>
<TABLE>
<CAPTION>
                                                                          INDIVIDUAL PRINCIPAL OCCUPATION OR
NAME AND BUSINESS ADDRESS                       OFFICE                        EMPLOYMENT (PRESENT/PAST)
- ---------------------------------  ---------------------------------  ------------------------------------------
<S>                                <C>                                <C>
C.H. van Kempen..................  Director                           Member of the Executive Board of Wolters
                                                                      Kluwer since 1993. Chief Executive Officer
                                                                      of Wolters Kluwer Italy, an indirect
                                                                      wholly owned subsidiary of Wolters Kluwer,
                                                                      from 1990 through 1993.
 
R. Pieterse......................  Director                           Member of the Executive Board since 1987.
 
Mary Martin Rogers...............  Director                           Chief Executive Officer of Lippincott-
  c/o Lippincott-Raven                                                Raven Publishers, Inc. since 1995. Prior
  Publishers, Inc.                                                    to 1995, Chief Executive Officer of Raven
  227 East Washington Square                                          Press, Ltd. for more than five years.
  Philadelphia, PA 19106
  (U.S. Citizen)
 
Hugh J. Yarrington...............  Director                           Chief Executive Officer of CCH
  c/o CCH Incorporated                                                Incorporated since 1996. Head of the
  2700 Lake Cook Road                                                 Knowledge Organization of CCH Incorporated
  Riverwoods, IL 60015                                                since 1993.
  (U.S. Citizen)
 
John Marozsan....................  Director                           Chief Operating Officer of CCH
  c/o CCH Incorporated                                                Incorporated since 1996. Prior to 1996,
  2700 Lake Cook Road                                                 President of Aspen Publishers, Inc. for
  Riverwoods, IL 60015                                                more than five years.
  (U.S. Citizen)
 
Bruce C. Lenz....................  Executive Vice President and       Executive Vice President and Chief
  c/o Wolters Kluwer               Chief Financial Officer            Financial Officer of WKUS for more than
  United States Inc.                                                  five years.
  161 N. Clark Street
  48th Floor
  Chicago, IL 60601-3221
  (U.S. Citizen)
</TABLE>
 
    4. DIRECTORS AND EXECUTIVE OFFICERS OF WK AMERICA.  The following table sets
forth the name, business address and present principal occupation or employment
and material occupations, positions, offices or employments for the past five
years of each Director and Executive Officer of WK America. Unless otherwise
indicated, each such person is a citizen of the Netherlands. Unless otherwise
indicated, each occupation set forth opposite an individual's name refers to
employment with WK America and the business address of each such person is c/o
Wolters Kluwer, Stadhouderskade 1, 1000 AV Amsterdam, the Netherlands.
 
<TABLE>
<CAPTION>
                                                                          INDIVIDUAL PRINCIPAL OCCUPATION OR
NAME AND BUSINESS ADDRESS                       OFFICE                        EMPLOYMENT (PRESENT/PAST)
- ---------------------------------  ---------------------------------  ------------------------------------------
<S>                                <C>                                <C>
Peter W. van Wel.................  Chairman of the Board and          Member of the Executive Board
  c/o Wolters Kluwer               President                          of Wolters Kluwer since 1993; President
  United States Inc.                                                  and Chief Executive Officer of WKUS from
  161 North Clark Street                                              1990 to 1993 and 1996 to the present.
  48th Floor
  Chicago, Il. 60601
</TABLE>
 
                                      I-4
<PAGE>
<TABLE>
<CAPTION>
                                                                          INDIVIDUAL PRINCIPAL OCCUPATION OR
NAME AND BUSINESS ADDRESS                       OFFICE                        EMPLOYMENT (PRESENT/PAST)
- ---------------------------------  ---------------------------------  ------------------------------------------
<S>                                <C>                                <C>
C.J. Brakel......................  Director                           Chairman of the Executive Board of Wolters
                                                                      Kluwer since 1995; member since 1981.
 
Bruce C. Lenz....................  Secretary and Treasurer            Executive Vice President and Chief
  c/o Wolters Kluwer                                                  Financial Officer of WKUS for more than
  United States Inc.                                                  five years.
  161 North Clark Street
  48th Floor
  Chicago, IL 60601
   (U.S. Citizen)
</TABLE>
 
    5. DIRECTORS AND EXECUTIVE OFFICERS OF THE PARENT The following table sets
forth the name, business address and present principal occupation or employment
and material occupations, positions, offices or employments for the past five
years of each Director and Executive Officer of the Parent. Unless otherwise
indicated, each such person is a citizen of the United States, and each
occupation set forth opposite an individual's name refers to employment with the
Parent.
 
<TABLE>
<CAPTION>
                                                                              INDIVIDUAL PRINCIPAL OCCUPATION OR
NAME AND BUSINESS ADDRESS                            OFFICE                        EMPLOYMENT (PRESENT/PAST)
- --------------------------------------  ---------------------------------  -----------------------------------------
<S>                                     <C>                                <C>
Jeffrey K. Smith......................  President, Treasurer and Clerk     President and Director since January,
  c/o Kluwer Academic Publishers B.V.                                      1997; Vice-President since 1983.
  Spuiboulevard 50
  3300 AZ Dordrecht
  the Netherlands
 
Zachary J. Rolnik.....................  Vice President and Assistant       Vice-President and Managing Director
  c/o Kluwer Boston, Inc.               Clerk                              since August, 1996; Senior Editor in
  101 Philip Drive                                                         Business and Economics Division since
  Norwell, MA 02061                                                        1990.
 
M. Stephen Dane.......................  Vice President and Assistant       Vice-President and General Manager since
  c/o Kluwer Boston, Inc.               Clerk                              1996; General Manager since 1987.
  101 Philip Drive
  Norwell, MA 02061
</TABLE>
 
    6. DIRECTORS AND EXECUTIVE OFFICERS OF THE OFFEROR. The following table sets
forth the name, business address and present principal occupation or employment
and material occupations, positions, offices or employments for the past five
years of each Director and Executive Officer of the Offeror. Unless otherwise
indicated, each such person is a citizen of the United States, and each
occupation set forth opposite an individual's name refers to employment with the
Parent.
 
<TABLE>
<CAPTION>
                                                                              INDIVIDUAL PRINCIPAL OCCUPATION OR
NAME AND BUSINESS ADDRESS                            OFFICE                        EMPLOYMENT (PRESENT/PAST)
- --------------------------------------  ---------------------------------  -----------------------------------------
<S>                                     <C>                                <C>
Jeffrey K. Smith......................  President, Treasurer and           President and Director since January,
  c/o Kluwer Academic Publishers B.V.   Secretary                          1997; Vice-President since 1983.
  Spuiboulevard 50
  3300 AZ Dordrecht
  The Netherlands
</TABLE>
 
                                      I-5
<PAGE>
<TABLE>
<CAPTION>
                                                                              INDIVIDUAL PRINCIPAL OCCUPATION OR
NAME AND BUSINESS ADDRESS                            OFFICE                        EMPLOYMENT (PRESENT/PAST)
- --------------------------------------  ---------------------------------  -----------------------------------------
<S>                                     <C>                                <C>
Zachary J. Rolnik.....................  Vice President and Assistant       Vice-President and Managing Director
  c/o Kluwer Boston, Inc.               Secretary                          since August, 1996; Senior Editor in
  101 Philip Drive                                                         Business and Economics Division since
  Norwell, MA 02061                                                        1990.
 
M. Stephen Dane.......................  Vice President and Assistant       Vice-President and General Manager since
  c/o Kluwer Boston, Inc.               Secretary                          1996; General Manager since 1987.
  101 Philip Drive
  Norwell, MA 02061
</TABLE>
 
                                      I-6
<PAGE>
    Facsimile copies of the Letter of Transmittal, properly completed and duly
executed, will be accepted. The Letter of Transmittal, certificates evidencing
Shares and any other required documents should be sent or delivered by each
stockholder or its broker, dealer, commercial bank or other nominee to the
Depositary as follows:
 
                        THE DEPOSITARY FOR THE OFFER IS:
                   MORGAN GUARANTY TRUST COMPANY OF NEW YORK
 
<TABLE>
<S>                                            <C>
                  BY MAIL:                                       BY HAND:
 
        Morgan Guaranty Trust Company            Securities Transfer & Reporting Services
          Corporate Reorganization                                (STARS)
                P.O. Box 8216                                   55 Broadway
            Boston, MA 02266-8216                                3rd Floor
                                                            New York, NY 10006
</TABLE>
 
<TABLE>
<S>                                            <C>
            BY OVERNIGHT COURIER:                       BY FACSIMILE TRANSMISSION:
 
        Morgan Guaranty Trust Company                         (781) 794-6333
  c/o State Street Corporate Reorganization
             70 Campanelli Drive                           CONFIRM BY TELEPHONE:
             Braintree, MA 02184                              (781) 794-6388
</TABLE>
 
    Questions or requests for assistance may be directed to the Information
Agent or to the Dealer Manager at their respective addresses and telephone
numbers set forth below. Additional copies of this Offer to Purchase, the Letter
of Transmittal and the Notice of Guaranteed Delivery may be obtained from the
Information Agent or the Dealer Manager and will be furnished promptly at the
Offeror's expense. A stockholder may also contact its broker, dealer, commecial
bank or trust company for assistance concerning the Offer.
 
                    THE INFORMATION AGENT FOR THE OFFER IS:
 
                                     [LOGO]
 
                               WALL STREET PLAZA
                            NEW YORK, NEW YORK 10005
                 BANKS AND BROKERS CALL COLLECT (212) 440-9800
                    ALL OTHERS CALL TOLL FREE (800) 223-2064
 
                      THE DEALER MANAGER FOR THE OFFER IS:
 
                     CREDIT SUISSE FIRST BOSTON CORPORATION
 
                             ELEVEN MADISON AVENUE
                            NEW YORK, NY 10010-3629
                         CALL TOLL FREE (800) 881-8320

<PAGE>
                             LETTER OF TRANSMITTAL
                                   To Tender
                             Shares of Common Stock
                                       of
 
                         Plenum Publishing Corporation
 
                       Pursuant to the Offer to Purchase
                              Dated June 16, 1998
                                       by
                             PPC Acquisition Corp.
                      a direct wholly owned subsidiary of
 
                              Kluwer Boston, Inc.
    THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK
      CITY TIME, ON WEDNESDAY, JULY 15, 1998, UNLESS THE OFFER IS EXTENDED
 
                        THE DEPOSITARY FOR THE OFFER IS:
                   MORGAN GUARANTY TRUST COMPANY OF NEW YORK
 
<TABLE>
<CAPTION>
                     BY MAIL:                                            BY HAND:
<S>                                                 <C>
          Morgan Guaranty Trust Company                           Securities Transfer &
             Corporate Reorganization                           Reporting Services (STARS)
                   PO Box 8216                                    55 Broadway 3rd Floor
              Boston, MA 02266-8216                                 New York, NY 10006
</TABLE>
 
<TABLE>
<S>                                                 <C>
              BY OVERNIGHT COURIER:                             BY FACSIMILE TRANSMISSION:
          Morgan Guaranty Trust Company                               (781) 794-6333
    c/o State Street Corporate Reorganization
               70 Campanelli Drive                                CONFIRM BY TELEPHONE:
               Braintree, MA 02184                                    (781) 794-6388
</TABLE>
 
    DELIVERY OF THIS LETTER OF TRANSMITTAL TO AN ADDRESS, OR TRANSMISSION OF
INSTRUCTIONS VIA A FACSIMILE TRANSMISSION OTHER THAN AS SET FORTH ABOVE WILL NOT
CONSTITUTE A VALID DELIVERY.
 
    This Letter of Transmittal is to be completed by stockholders of Plenum
Publishing Corporation either if certificates evidencing shares of Common Stock
(as defined below) are to be forwarded herewith or if a tender of such shares is
to be made by book-entry transfer to the account of Morgan Guaranty Trust
Company of New York, as Depositary (the "Depositary"), at The Depository Trust
Company (the "Book-Entry Transfer Facility") pursuant to the procedures set
forth in Section 3--"Procedures for Tendering Shares" of the Offer to Purchase
(as defined below). Delivery of documents to the Book-Entry Transfer Facility
does not constitute delivery to the Depositary.
 
    Holders of shares of Common Stock whose certificates are not immediately
available, or who are unable to deliver their certificates and all other
documents required by this Letter of Transmittal to the Depositary on or prior
to the Expiration Date (as defined in Section 1--"Terms of the Offer" of the
Offer to Purchase) or who cannot complete the procedure for delivery by
book-entry transfer on a timely basis and who wish to tender their shares must
tender their shares pursuant to the guaranteed delivery procedure set forth in
Section 3--"Procedures for Tendering Shares" of the Offer to Purchase. See
Instruction 2 of this Letter of Transmittal.
<PAGE>
/ /  CHECK HERE IF SHARES ARE BEING DELIVERED BY BOOK-ENTRY TRANSFER TO THE
    DEPOSITARY'S ACCOUNT AT THE BOOK-ENTRY TRANSFER FACILITY AND COMPLETE THE
    FOLLOWING:
    Name(s) of Tendering Institution____________________________________________
   Account Number_______________________________________________________________
   Transaction Code Number______________________________________________________
 
/ /  CHECK HERE IF SHARES ARE BEING TENDERED PURSUANT TO A NOTICE OF GUARANTEED
    DELIVERY PREVIOUSLY SENT TO THE DEPOSITARY AND COMPLETE THE FOLLOWING:
   Name(s) of Registered Holder(s)______________________________________________
   Window Ticket Number (if any)________________________________________________
   Date of Execution of Notice of Guaranteed Delivery___________________________
   Name of Institution Which Guaranteed Delivery________________________________
 
   If Delivery by Book-Entry Transfer:
    Account Number______________________________________________________________
    Transaction Code Number_____________________________________________________
 
<TABLE>
<CAPTION>
                            DESCRIPTION OF SHARES OF COMMON STOCK TENDERED
   Name(s) and Address(es) of Registered Holder(s)
    (Please fill in, if blank, exactly as name(s)                  Certificate(s) Tendered
              appear(s) on certificate(s))               (Attach Additional Signed List if Necessary)
<S>                                                     <C>             <C>             <C>
                                                                         Total Number
                                                         Certificate      of Shares         Number
                                                          Number(s)*     Evidenced by     of Shares
                                                                        Certificate(s)*   Tendered**
                                                         Total shares of Common Stock
</TABLE>
 
 *   Need not be completed by stockholders delivering shares of Common Stock by
     book-entry transfer.
 **  Unless otherwise indicated, it will be assumed that all shares of Common
     Stock evidenced by each certificate delivered to the Depositary are being
     tendered. See Instruction 4 of this Letter of Transmittal.
     The names and addresses of the registered holders should be printed, if
 not already printed above, exactly as they appear on the certificates
 representing shares of Common Stock tendered hereby. The certificates and the
 number of shares of Common Stock that the undersigned wishes to tender should
 be indicated in the appropriate boxes.
 
 / /  CHECK HERE IF TENDER IS BEING MADE PURSUANT TO LOST OR MUTILATED
     SECURITIES. SEE INSTRUCTION 10.
 
                                       2
<PAGE>
                    NOTE: SIGNATURES MUST BE PROVIDED BELOW.
              PLEASE READ THE ACCOMPANYING INSTRUCTIONS CAREFULLY.
 
 Ladies and Gentlemen:
 
     The undersigned hereby tenders to PPC Acquisition Corp., a Delaware
 corporation (the "Offeror") and a direct wholly owned subsidiary of Kluwer
 Boston, Inc., a Massachusetts corporation (the "Parent"), the above described
 shares of Common Stock, par value $.10 per share (the "Common Stock"), of
 Plenum Publishing Corporation, a Delaware corporation (the "Company"),
 pursuant to the Offeror's offer to purchase all outstanding shares of Common
 Stock (the "Shares"), at a purchase price of $73.50 per Share net to the
 seller in cash, without interest thereon (such price or such higher price per
 share as may be paid in the Offer (as defined below), referred to herein as
 the "Offer Price"), upon the terms and subject to the conditions set forth in
 the Offer to Purchase, dated June 16, 1998 (the "Offer to Purchase"), receipt
 of which is hereby acknowledged, and in this Letter of Transmittal (which,
 together with any amendments or supplements thereto, constitute the "Offer").
 
     Subject to, and effective upon, the acceptance for payment of the Shares
 tendered herewith, in accordance with the terms and subject to the conditions
 of the Offer (including, if the Offer is extended or amended, the terms and
 conditions of such extension or amendment), the undersigned hereby sells,
 assigns and transfers to, or upon the order of, the Offeror, all right, title
 and interest in and to all of the Shares tendered hereby and all dividends
 (other than quarterly cash dividends having a record date prior to the Offeror
 purchasing and becoming a record holder of such Shares), distributions
 (including, without limitation, distributions of additional Shares) and rights
 declared, issued, paid or distributed in respect of such Shares on or after
 June 10, 1998 and payable or distributable to the undersigned on a date prior
 to the transfer to the name of the Offeror (or nominee or transferee of the
 Offeror) on the Company's stock transfer records of the Shares tendered
 herewith (collectively, "Distributions") and irrevocably constitutes and
 appoints Jeffrey K. Smith and Bruce C. Lenz, and each of them, as the true and
 lawful agent and attorney-in-fact of the undersigned with respect to such
 Shares and all Distributions with full power of substitution (such power of
 attorney being deemed to be an irrevocable power coupled with an interest) to
 (i) deliver certificates for such Shares and all Distributions or transfer
 ownership of such Shares and all Distributions on the account books maintained
 by the Book-Entry Transfer Facility, together, in either case, with all
 accompanying evidences of transfer and authenticity, to or upon the order of
 the Offeror, upon receipt by the Depositary, as the undersigned's agent, of
 the Offer Price, (ii) present such Shares and all Distributions for transfer
 on the books of the Company and (iii) receive all benefits and otherwise
 exercise all rights of beneficial ownership of such Shares and all
 Distributions, all in accordance with the terms and subject to the conditions
 of the Offer.
 
     The undersigned hereby irrevocably appoints Jeffrey K. Smith and Bruce C.
 Lenz, and each of them, as the attorney-in-fact and proxy of the undersigned,
 each with full power of substitution, to vote in such manner as each such
 attorney and proxy or the substitute for any such attorney and proxy shall, in
 the sole discretion of each such attorney and proxy, deem proper, and
 otherwise act (by written consent or otherwise) with respect to all of the
 Shares tendered hereby (and any Distributions) which the undersigned is
 entitled to vote at any meeting of stockholders of the Company (whether annual
 or special and whether or not adjourned or postponed), or consent in lieu of
 any such meeting or otherwise. This power of attorney and proxy is irrevocable
 and is granted in consideration of, and is effective upon, the Offeror's oral
 or written notice to the Depositary of its acceptance for payment of such
 shares in accordance with the terms of the Offer. Such acceptance for payment
 shall revoke all other powers of attorney and proxies given by the undersigned
 at any time with respect to such shares (and any Distributions), and no
 subsequent powers of attorney or proxies may be given (and if given or
 executed shall not be effective) by the undersigned with respect thereto. The
 undersigned acknowledges and understands that in order for shares to be deemed
 validly tendered, immediately upon the Offeror's acceptance for payment of
 such shares, the Offeror must be able to exercise full voting power and other
 rights of a record and beneficial holder, including, without limitation,
 voting at any meeting of the Company's stockholders or acting by written
 consent, with respect to such shares (and any Distributions).
 
                                       3
<PAGE>
     The undersigned hereby represents and warrants that: (i) the undersigned
 has full power and authority to tender, sell, assign and transfer the shares
 tendered hereby (and any Distributions) and (ii) when the same are accepted
 for payment by the Offeror, the Offeror will acquire good, marketable and
 unencumbered title thereto, free and clear of all liens, restrictions,
 charges, claims and encumbrances, and that none of such Shares and
 Distributions will be subject to any adverse claim. The undersigned, upon
 request, shall execute and deliver all additional documents deemed by the
 Depositary or the Offeror to be necessary or desirable to complete the sale,
 assignment and transfer of the Shares tendered hereby and all Distributions.
 In addition, the undersigned shall remit and transfer promptly to the
 Depositary for the account of the Offeror all Distributions in respect of the
 shares tendered hereby, accompanied by appropriate documentation of transfer,
 and, pending such remittance and transfer or appropriate assurance thereof,
 the Offeror shall be entitled, subject to applicable law, to all rights and
 privileges as owner of each such Distribution and may withhold the entire
 Offer Price or deduct from the Offer Price the amount or value of such
 Distribution as determined by the Offeror in its sole discretion.
 
     No authority conferred herein or agreed to be conferred herein shall be
 affected by, and all such authority shall survive, the death or incapacity of
 the undersigned. All obligations of the undersigned hereunder shall be binding
 upon the heirs, executors, administrators, trustees in bankruptcy, personal
 and legal representatives, successors and assigns of the undersigned. Except
 as described in Section 4--"Withdrawal Rights" of the Offer to Purchase, this
 tender is irrevocable.
 
     The undersigned understands that the acceptance for payment of tendered
 Shares by the Offeror pursuant to any of the procedures described in Section
 2--"Acceptance for Payment and Payment for Shares" of the Offer to Purchase
 and in the instructions hereto will constitute the undersigned's acceptance of
 the terms and conditions of the Offer. The undersigned recognizes that under
 certain circumstances set forth in the Offer to Purchase, the Offeror may not
 be required to accept for payment any of the Shares tendered hereby.
 
     Unless otherwise indicated herein in the box entitled "Special Payment
 Instructions," please issue the check for the Offer Price for all shares
 purchased and return any certificates for Shares not tendered or not
 purchased, in the name(s) of the registered holder(s) appearing above under
 "Description of Shares of Common Stock Tendered." Similarly, unless otherwise
 indicated in the box entitled "Special Delivery Instructions," please mail the
 check for the Offer Price for all Shares purchased and return any certificates
 for any Shares not tendered or not purchased (and accompanying documents, as
 appropriate) to the address(es) of the registered holder(s) appearing above
 under "Description of Shares of Common Stock Tendered." If the boxes entitled
 "Special Delivery Instructions" and "Special Payment Instructions" are both
 completed, please issue the check for the Offer Price for all Shares purchased
 and return any certificates for Shares not tendered or not purchased in the
 name(s) of, and deliver said check and/or certificate(s) to, the person(s) so
 indicated. Unless otherwise indicated in the box entitled "Special Payment
 Instructions," in the case of a book-entry delivery of Shares, please credit
 the account maintained at the Book-Entry Transfer Facility with any Shares not
 purchased. The undersigned recognizes that the Offeror has no obligation
 pursuant to the Special Payment Instructions to transfer any Shares from the
 name(s) of the registered holder(s) thereof if the Offeror does not accept for
 payment any of the Shares tendered hereby.
 
                                       4
<PAGE>
                          SPECIAL PAYMENT INSTRUCTIONS
                        (See Instructions 1, 5, 6 and 7)
 
 To be completed ONLY if the check for the Offer Price of Shares purchased or
 certificates for Shares not tendered or not purchased are to be issued in the
 name of someone other than the undersigned.
 
 Issue / / Check  / / Certificate(s) to:
 Name _________________________________________________________________________
 
                                 (PLEASE PRINT)
 Address ______________________________________________________________________
                                                             (INCLUDE ZIP CODE)
  _____________________________________________________________________________
 (Recipient's Tax Identification or Social Security No.)
 (See Substitute W-9 on reverse side)
 
                         SPECIAL DELIVERY INSTRUCTIONS
                        (See Instructions 1, 5, 6 and 7)
 
 To be completed ONLY if the check for the Offer Price of Shares purchased or
 certificates for Shares not tendered or not purchased are to be sent to
 someone other than the undersigned, or to the undersigned at an address other
 than that shown under "Description of Shares of Common Stock Tendered."
 
 Issue / / Check  / /  Certificate(s) to:
 
 Name _________________________________________________________________________
 
                                 (PLEASE PRINT)
 
 Address ______________________________________________________________________
 
  _____________________________________________________________________________
 
                                                             (INCLUDE ZIP CODE)
 
                                       5
<PAGE>
 
                                   IMPORTANT
                            STOCKHOLDERS: SIGN HERE
              (ALSO COMPLETE SUBSTITUTE FORM W-9 ON REVERSE SIDE)
 ______________________________________________________________________________
 ______________________________________________________________________________
 
                         (SIGNATURES OF STOCKHOLDER(S))
 Dated: ________________________
 
 (Must be signed by registered holder(s) exactly as name(s) appear(s) on stock
 certificates or on a security position listing or by person(s) authorized to
 become registered holder(s) by certificate(s) and documents transmitted
 herewith. If signature is by a trustee, executor, administrator, guardian,
 attorney-in-fact, officer of a corporation or other person acting in a
 fiduciary or representative capacity, please provide the following
 information. See Instruction 5.)
 Name(s) ______________________________________________________________________
 ______________________________________________________________________________
 ______________________________________________________________________________
 
                                 (PLEASE PRINT)
 Capacity (Full Title) ________________________________________________________
 
 Address
 ______________________________________________________________________________
 
                                                             (INCLUDE ZIP CODE)
 Area Code and Telephone Number _______________________________________________
 Tax Identification or Social Security Number _________________________________
 
                                      (See Substitute Form W-9 on reverse side)
 
                           GUARANTEE OF SIGNATURE(S)
 
                   (IF REQUIRED -- SEE INSTRUCTIONS 1 AND 5)
 
                    FOR USE BY FINANCIAL INSTITUTIONS ONLY.
             PLACE MEDALLION GUARANTEE OVER THE BELOW INFORMATION.
 Authorized Signature(s) ______________________________________________________
 Name _________________________________________________________________________
 
                                 (PLEASE PRINT)
 Name of Firm _________________________________________________________________
 Address ______________________________________________________________________
 
                               (INCLUDE ZIP CODE)
 Area Code and Telephone Number _______________________________________________
 Dated: _______________________________________________________________________
 
                                       6
<PAGE>
                                  INSTRUCTIONS
             Forming Part of the Terms and Conditions of the Offer
 
    1. SIGNATURE GUARANTEE. No signature guarantee on this Letter of Transmittal
is required if (i) this Letter of Transmittal is signed by the registered
holder(s) (which term, for purposes of this document, shall include any
participant in the Book-Entry Transfer Facility whose name appears on a security
position listing as the owner of Shares tendered herewith, unless such holder(s)
have completed either the box entitled "Special Delivery Instructions" or
"Special Payment Instructions" on this Letter of Transmittal) or (ii) such
Shares are tendered for the account of a financial institution (including most
commercial banks, savings and loan associations and brokerage houses) that is a
participant in the Security Transfer Agents Medallion Program, the New York
Stock Exchange Medallion Signature Guarantee Program or the Stock Exchange
Medallion Program (each, an "Eligible Institution"). In all other cases, all
signatures on this Letter of Transmittal must be guaranteed by an Eligible
Institution.
 
    2. DELIVERY OF LETTER OF TRANSMITTAL AND CERTIFICATES. This Letter of
Transmittal is to be completed by stockholders either if certificates are to be
forwarded herewith or unless an Agent's Message (as defined in Section
2--"Acceptance for Payment and Payment for Shares" of the Offer to Purchase) is
utilized, if tenders are to be made pursuant to the procedures for delivery by
book-entry transfer set forth in Section 3--"Procedures for Tendering Shares" of
the Offer to Purchase. Certificates for all physically tendered Shares, or
timely confirmation of a book-entry transfer (a "Book Entry Confirmation") into
the Depositary's account at the Book-Entry Transfer Facility of all Shares
delivered by book-entry transfer, this Letter of Transmittal (or manually signed
facsimile hereof) properly completed and duly executed with all required
signature guarantees and any other documents required by this Letter of
Transmittal, must be received by the Depositary at the address set forth herein
on or prior to the Expiration Date (as defined in Section 1--"Terms of the
Offer" of the Offer to Purchase), or the tendering stockholder must comply with
the guaranteed delivery procedures set forth below. If certificates are
forwarded to the Depositary in multiple deliveries, this Letter of Transmittal
(or manually signed facsimile hereof) properly completed and duly executed with
all required signature guarantees must accompany each such delivery.
 
    Stockholders whose certificates for Shares are not immediately available,
who cannot deliver their certificates and all other required documents to the
Depositary on or prior to the Expiration Date, or who cannot complete the
procedure for delivery by book-entry transfer on a timely basis, may tender
their Shares pursuant to the guaranteed delivery procedures set forth in Section
3--"Procedures for Tendering Shares" of the Offer to Purchase. Pursuant to such
procedures, (i) such tender must be made by or through an Eligible Institution,
(ii) a properly completed and duly executed Notice of Guaranteed Delivery,
substantially in the form provided by the Offeror, must be received by the
Depositary, either by hand delivery, mail or facsimile transmission, on or prior
to the Expiration Date and (iii) the certificates for all physically tendered
shares, in proper form for transfer (or Book-Entry Confirmation) together with
this Letter of Transmittal (or manually signed facsimile thereof) properly
completed and duly executed with all required signature guarantees or, in the
case of a book-entry transfer, an Agent's Message, and any other documents
required by this Letter of Transmittal, must be received by the Depositary
within three trading days after the date of the execution and delivery to the
Depositary of the Notice of Guaranteed Delivery. A trading day is any day on
which the NASDAQ National Market is open for business.
 
    The method of delivery of this Letter of Transmittal, the certificates for
Shares and all other required documents, including delivery through the
Book-Entry Transfer Facility, is at the option and risk of the tendering
stockholder. If delivery is by mail, registered mail with return receipt
requested, properly insured, is recommended. In all cases, sufficient time
should be allowed for such documents to reach the Depositary. Except as
otherwise provided in this Instruction 2, delivery will be deemed made only when
actually received by the Depositary.
 
    No alternative, conditional or contingent tenders will be accepted and no
fractional shares will be purchased. All tendering stockholders, by execution of
this Letter of Transmittal (or a facsimile hereof), waive any right to receive
any notice of the acceptance of their Shares for payment.
 
    3. INADEQUATE SPACE. If the space provided herein under "Description of
Shares of Common Stock Tendered" is inadequate, the certificate numbers, the
number of Shares evidenced by such certificates and the number of Shares
tendered should be listed on a separate signed schedule and attached hereto.
 
                                       7
<PAGE>
    4. PARTIAL TENDERS (NOT APPLICABLE TO STOCKHOLDERS WHO TENDER BY BOOK-ENTRY
TRANSFER). If fewer than all the Shares evidenced by any certificate delivered
to the Depositary herewith are to be tendered, fill in the number of Shares that
are to be tendered in the box entitled "Number of Shares Tendered." In such
case, as soon as practicable after the Expiration Date, new certificate(s)
evidencing the remainder of the Shares that were evidenced by the certificates
delivered to the Depositary herewith will be sent to the person(s) signing this
Letter of Transmittal, unless otherwise provided in the box entitled "Special
Delivery Instructions." All Shares represented by certificates delivered to the
Depositary will be deemed to have been tendered unless otherwise indicated.
 
    5. SIGNATURES ON LETTER OF TRANSMITTAL, STOCK POWERS AND ENDORSEMENTS. If
this Letter of Transmittal is signed by the registered holder(s) of the Shares
tendered hereby, the signature(s) must correspond with the name(s) as written on
the certificates without alteration, enlargement or any other change whatsoever.
Do not sign the back of the certificates.
 
    If any Share tendered hereby is held of record by two or more holders, all
such holders must sign this Letter of Transmittal.
 
    If any of the Shares tendered hereby are registered in names of different
holders, it will be necessary to complete, sign and submit as many separate
Letters of Transmittal as there are different registrations of certificates.
 
    If this Letter of Transmittal is signed by the registered holder(s) of the
Shares tendered hereby, no endorsements of certificates or separate stock powers
are required unless payment is to be made, or certificates for Shares not
tendered or not purchased are to be issued in the name of, a person other than
the registered holder(s), in which case the certificate(s) tendered hereby must
be endorsed or accompanied by appropriate stock powers, in either case signed
exactly as the name(s) of the registered holder(s) appear(s) on such
certificate(s), and stock powers must be guaranteed by an Eligible Institution.
 
    If this Letter of Transmittal is signed by a person other than the
registered owner(s) of the Shares tendered hereby, the certificates tendered
hereby must be endorsed or accompanied by appropriate stock powers, in either
case signed as the name(s) of the registered holder(s) appear(s) on such
certificates. Signatures on such certificates and stock powers must be
guaranteed by an Eligible Institution.
 
    If this Letter of Transmittal or any certificate or stock power is signed by
a trustee, executor, administrator, guardian, attorney-in-fact, agent, officer
of a corporation or other person acting in a fiduciary or representative
capacity, such person should so indicate when signing, and proper evidence
satisfactory to the Offeror of such person's authority to so act must be
submitted.
 
    6. SPECIAL PAYMENT AND DELIVERY INSTRUCTIONS. If a check for the Offer Price
of any Shares tendered hereby is to be issued or certificate(s) not tendered or
not purchased are to be issued in the name of a person other than the person
signing this Letter of Transmittal, or to the person(s) signing this Letter of
Transmittal but at an address other than that shown above, the appropriate boxes
on this Letter of Transmittal must be completed.
 
    7. STOCK TRANSFER TAXES. Except as set forth in this Instruction 7, the
Offeror will pay or cause to be paid any stock transfer taxes with respect to
the transfer and sale of the purchased Shares to it, or to its order, pursuant
to the Offer. If, however, payment of the Offer Price of any Shares purchased is
to be made to, or certificate(s) for Shares not tendered or not purchased are to
be issued in the name of, a person other than the registered owner(s), or if
tendered certificates are registered in the name of any persons other than the
persons signing this Letter of Transmittal, the amount of any stock transfer
taxes (whether imposed on the registered holder(s), such other person or
otherwise) payable on account of the transfer to such other person will be
deducted from the Offer Price of such shares purchased, unless evidence
satisfactory to the Offeror of the payment of such taxes or exemption therefrom
is submitted.
 
    8. WAIVER OF CONDITIONS. Subject to the terms of the Merger Agreement (as
defined in the Offer to Purchase), the conditions of the Offer may be waived by
the Offeror, in whole or in part, at any time and from time to time in Offeror's
sole discretion, in the case of any Shares tendered.
 
                                       8
<PAGE>
    9. SUBSTITUTE FORM W-9. Each tendering stockholder is required to provide
the Depositary with a correct taxpayer identification number ("TIN"), generally
the stockholder's social security or federal employer identification number, and
with certain other information, on the Substitute Form W-9, which is provided
under "Important Tax Information" below, and to certify, under penalties of
perjury, that such number is correct and that the stockholder is not subject to
backup withholding of federal income tax. If a tendering stockholder has been
notified by the Internal Revenue Service that such stockholder is subject to
backup withholding, such stockholder must cross out item (2) of the
Certification box (Part 2) of the Substitute Form W-9, unless such stockholder
has since been notified by the Internal Revenue Service that such stockholder is
no longer subject to backup withholding. Failure to provide the information on
the Substitute Form W-9 may subject the tendering stockholder to 31% federal
income tax withholding on the payment of the Offer Price of all Shares purchased
from such stockholder. The box in Part 3 of the Substitute Form W-9 may be
checked if the tendering stockholder has not been issued a TIN and has applied
for a TIN or intends to apply for a TIN in the near future. If the box in Part 3
is checked and the Depositary is not provided with the TIN within 60 days, the
Depositary will withhold 31% on all payments of the Purchase Price to such
stockholder until a TIN is provided to the Depositary.
 
    10. LOST, DESTROYED OR STOLEN CERTIFICATES. If any certificate(s)
representing shares has been lost, destroyed or stolen, the stockholder should
promptly notify Securities Transfer Corp. at (972) 447-9890. The stockholder
will then be instructed as to the steps that must be taken in order to replace
the certificate(s). This Letter of Transmittal and related documents cannot be
processed until the procedures for replacing lost or destroyed certificates have
been followed.
 
    11. REQUESTS FOR ASSISTANCE OR ADDITIONAL COPIES. Questions or requests for
assistance may be directed to the Information Agent or the Dealer Manager at
their respective addresses and telephone numbers set forth below. Additional
copies of the Offer to Purchase, this Letter of Transmittal, the Notice of
Guaranteed Delivery and the Guidelines for Certification of Taxpayer
Identification Number on Substitute Form W-9 may be obtained from the
Information Agent or the Dealer Manager at the addresses set forth below or from
brokers, dealers, commercial banks or trust companies and such materials will be
furnished at the Offeror's expense.
 
    IMPORTANT: This Letter of Transmittal (or manually signed facsimile hereof)
properly completed and duly executed (with all required guarantees and
certificates or confirmation of book-entry transfer and all other required
documents) or the Notice of Guaranteed Delivery properly completed and duly
executed must be received by the Depositary on or prior to the Expiration Date.
 
                                       9
<PAGE>
                           IMPORTANT TAX INFORMATION
 
    Under federal income tax law, a stockholder whose tendered Shares are
accepted for payment is required to provide the Depositary (as payer) with such
stockholder's current TIN on Substitute Form W-9 below. If such stockholder is
an individual, the TIN is such stockholder's social security number. If the
Depositary is not provided with the correct TIN, the stockholder or other payee
may be subject to a $50 penalty imposed by the Internal Revenue Service. In
addition, payments that are made to such stockholder or other payee with respect
to shares purchased pursuant to the Offer may be subject to backup withholding
of 31%.
 
    Certain stockholders (including, among others, all corporation, and certain
foreign individuals) are not subject to these backup withholding and reporting
requirements. In order for a foreign individual or a foreign entity to qualify
as an exempt recipient, that stockholder must submit to the Depositary a
properly completed Internal Revenue Service Form W-8 (a "Form W-8"), signed
under penalties of perjury, attesting to that individual's exempt status. A Form
W-8 can be obtained from the Depositary. See the enclosed "Guidelines for
Certification of Taxpayer Identification Number on Substitute Form W-9" for
additional instructions.
 
    If backup withholding applies, the Depositary is required to withhold 31% of
any payment made to the stockholder or other payee. Backup withholding is not an
additional tax. Rather, the federal income tax liability of persons subject to
backup withholding will be reduced by the amount of tax withheld. If withholding
results in an overpayment of taxes, a refund may be obtained from the Internal
Revenue Service.
 
Purpose of Substitute Form W-9
 
    To prevent backup withholding on payments made to a stockholder or other
payee with respect to shares purchased pursuant to the Offer, the stockholder is
required to notify the Depositary of the stockholder's current TIN (or the TIN
of any other payee) by completing the form below, certifying that the TIN
provided on Substitute Form W-9 is correct (or that such stockholder is awaiting
a TIN), and that (1) the stockholder has not been notified by the Internal
Revenue Service that the stockholder is subject to backup withholding as a
result of failure to report all interest or dividends or (2) the Internal
Revenue Service has notified the stockholder that the stockholder is no longer
subject to backup withholding.
 
What Number to Give the Depositary
 
    The stockholder is required to give the Depositary the TIN (e.g., social
security number or employer identification number) of the record owner of the
shares tendered hereby. If the shares are registered in more than one name or
are not registered in the name of the actual owner, consult the enclosed
"Guidelines for Certification of Taxpayer Identification Number on Substitute
Form W-9" for additional guidance on which number to report.
 
                                       10
<PAGE>
            PAYER'S NAME: MORGAN GUARANTY TRUST COMPANY OF NEW YORK
 
<TABLE>
<S>                                   <C>                                              <C>
- -----------------------------------------------------------------------------------------------------------------------
 
SUBSTITUTE Form W-9                   Part 1--PLEASE PROVIDE YOUR TIN IN THE BOX AT       Social Security number or
Department of the Treasury            RIGHT AND CERTIFY BY SIGNING AND DATING BELOW.    Employer identification number
Internal Revenue Service
                                      ---------------------------------------------------------------------------------
 Payer's Request for Taxpayer         Part 2--Certification--Under penalties of perjury, I certify that:
 Identification Number ("TIN")
                                      ---------------------------------------------------------------------------------
(1) The number shown on this form is my correct Taxpayer Identification Number (or I am waiting for a number to be
issued to me), and
 
(2)I am not subject to backup withholding because: (a) I am exempt from backup withholding, or (b) I have not been
   notified by the Internal Revenue Service (IRS) that I am subject to backup withholding as a result of a failure to
   report all interest or dividends, or (c) the IRS has notified me that I am no longer subject to backup withholding.
 
CERTIFICATION INSTRUCTIONS--You must cross out item (2) above if you have been notified by the IRS that you are
currently subject to backup withholding because of underreporting interest or dividends on your tax return. However, if
after being notified by the IRS that you were subject to backup withholding you received another notification from the
IRS that you are no longer subject to backup, do not cross out item (2).
                                      ---------------------------------------------------------------------------------
                                                                                                   Part 3--
                                                                                               Awaiting TIN / /
SIGNATURE   DATE
                                      ---------------------------------------------------------------------------------
</TABLE>
 
NOTE: FAILURE TO COMPLETE AND RETURN THIS FORM MAY RESULT IN BACKUP WITHHOLDING
      OF 31% OF ANY PAYMENTS MADE TO YOU PURSUANT TO THE OFFER. PLEASE REVIEW
      THE ENCLOSED GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION
      NUMBER ON SUBSTITUTE FORM W-9 FOR ADDITIONAL DETAILS.
 
           YOU MUST COMPLETE THE FOLLOWING CERTIFICATE IF YOU CHECKED
                 THE BOX IN PART 3 OF THE SUBSTITUTE FORM W-9.
 
             CERTIFICATE OF AWAITING TAXPAYER IDENTIFICATION NUMBER
 
      I certify under penalties of perjury that a taxpayer identification
  number has not been issued to me, and either (1) I have mailed or delivered
  an application to receive a taxpayer identification number to the
  appropriate Internal Revenue Service Center or Social Security
  Administration Office or (2) I intend to mail or deliver an application in
  the near future. I understand that if I do not provide a taxpayer
  identification number, 31% of all reportable payments made to me will be
  withheld, but that such amounts will be refunded to me if I then provide a
  taxpayer identification number within 60 days.
  Signature ____________________________  Date ___________________
 
                                       11
<PAGE>
                    THE INFORMATION AGENT FOR THE OFFER IS:
 
                                     [LOGO]
 
                               Wall Street Plaza
                            New York, New York 10005
                 Banks and Brokers Call Collect (212) 440-9800
                    All Others Call Toll Free (800) 223-2064
 
                      THE DEALER MANAGER FOR THE OFFER IS:
 
                     Credit Suisse First Boston Corporation
 
                             Eleven Madison Avenue
                         New York, New York 10010-3629
                         Call Toll Free (800) 881-8320
 
                                       12

<PAGE>
                         Notice of Guaranteed Delivery
 
                                      for
 
                        Tender of Shares of Common Stock
 
                                       of
 
                           Plenum Publishing Company
 
    THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK
     CITY TIME, ON WEDNESDAY, JULY 15, 1998, UNLESS THE OFFER IS EXTENDED.
 
    This form, or one substantially equivalent hereto, must be used to accept
the Offer (as defined below) if certificates for shares of Common Stock, par
value $.10 per share (the "Shares"), of Plenum Publishing Corporation, a
Delaware corporation (the "Company"), are not immediately available or if the
procedure for book-entry transfer cannot be completed on a timely basis or time
will not permit all required documents to reach the Depositary on or prior to
the Expiration Date (as defined in the Offer to Purchase). This form may be
delivered by hand, facsimile transmission, or mail to the Depositary. See
Section 3--"Procedure for Tendering Shares" of the Offer to Purchase, dated June
16, 1998 (the "Offer to Purchase").
 
                        The Depositary for the Offer is:
 
                         MORGAN GUARANTY TRUST COMPANY
                                  OF NEW YORK
 
<TABLE>
<CAPTION>
                  BY MAIL:                                       BY HAND:
<S>                                            <C>
        Morgan Guaranty Trust Company                      Securities Transfer &
          Corporate Reorganization                      Reporting Services (STARS)
                 PO Box 8216                                    55 Broadway
            Boston, MA 02266-8216                                3rd Floor
                                                            New York, NY 10006
</TABLE>
 
<TABLE>
<CAPTION>
            BY OVERNIGHT COURIER:                       BY FACSIMILE TRANSMISSION:
<S>                                            <C>
        Morgan Guaranty Trust Company                         (781) 794-6333
  c/o State Street Corporate Reorganization
             70 Campanelli Drive                           CONFIRM BY TELEPHONE:
             Braintree, MA 02184                              (781) 794-6388
</TABLE>
 
    DELIVERY OF THIS NOTICE OF GUARANTEED DELIVERY TO AN ADDRESS, OR
TRANSMISSION OF INSTRUMENTS VIA A FACSIMILE, OTHER THAN AS SET FORTH ABOVE DOES
NOT CONSTITUTE A VALID DELIVERY.
 
    This Notice of Guaranteed Delivery is not to be used to guarantee
signatures. If a signature on a Letter of Transmittal is required to be
guaranteed by an "Eligible Institution" under the instructions thereto, such
signature guarantee must appear in the applicable space provided in the
signature box on the Letter of Transmittal.
 
    The Eligible Institution that completes this form must communicate the
guarantee to the Depositary and must deliver the Letter of Transmittal or an
Agent's Message and certificates for Shares to the Depositary within the time
period shown herein. Failure to do so could result in a financial loss to such
Eligible Institution.
 
              THE GUARANTEE ON THE REVERSE SIDE MUST BE COMPLETED.
<PAGE>
Ladies and Gentlemen:
 
    The undersigned hereby tenders to PPC Acquisition Corp., a Delaware
corporation, upon the terms and subject to the conditions set forth in the Offer
to Purchase and in the related Letter of Transmittal (which, together with all
amendments or supplements thereto, constitute the "Offer"), receipt of which is
hereby acknowledged, the number of Shares of the Company indicated below,
pursuant to the guaranteed delivery procedure set forth in Section
3--"Procedures for Tendering Shares" of the Offer to Purchase.
 
<TABLE>
<S>                                           <C>
Number of Shares:                             Sign Here
Certificate No(s). (if available):            Name(s):
 
If Securities will be tendered by book-entry transfer:
Name of Tendering Institution:                Address:
Account No.: at                                                                 (Zip Code)
(Please Print)                                Area Code and Telephone No:
                                              Signature(s):
</TABLE>
<PAGE>
                                   GUARANTEE
                    (Not to be used for signature guarantee)
 
    The undersigned, a bank, broker, dealer, credit union, savings association
or other entity which is a member in good standing of the Securities Transfer
Agents Medallion Program or a bank, broker, dealer, credit union, savings
association or other entity which is an "eligible guarantor institution," as
such term is defined in Rule l7Ad-15 under the Securities Exchange Act of 1934,
as amended, guarantees the delivery to the Depositary of the Shares tendered
hereby, together with a properly completed and duly executed Letter of
Transmittal (or manually signed facsimile(s) thereof) and any other required
documents, or an Agent's Message (as defined in the Offer to Purchase) in the
case of a book-entry delivery of Shares, all within three NASDAQ trading days of
the date hereof.
 
Name of Firm: __________________________________________________________________
 
Address: _______________________________________________________________________
 
                                                                      (Zip Code)
 
AUTHORIZED SIGNATURE: __________________________________________________________
 
Title: _________________________________________________________________________
 
Name: __________________________________________________________________________
                             (Please Print or Type)
 
Area Code & Telephone No.: _____________________________________________________
 
   NOTE: DO NOT SEND SHARE CERTIFICATES WITH THIS NOTICE OF GUARANTEED DELIVERY.
         SHARE CERTIFICATES SHOULD BE SENT WITH YOUR LETTER OF TRANSMITTAL.
 
Date: ____________________________, 1998

<PAGE>
                                                         CREDIT SUISSE FIRST
BOSTON CORPORATION
 
        [LOGO]
                                                         Eleven Madison
Avenue          Telephone 212 325 2000
                                                         New York, NY 10010-3629
 
                           Offer to Purchase for Cash
 
                           All Outstanding Shares of
 
                                  Common Stock
 
                                       of
 
                         Plenum Publishing Corporation
                                       at
 
                              $73.50 Net Per Share
 
                                       by
 
                             PPC Acquisition Corp.
 
                      a direct wholly owned subsidiary of
 
                              Kluwer Boston, Inc.
 
    THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK
      CITY TIME, ON WEDNESDAY, JULY 15, 1998 UNLESS THE OFFER IS EXTENDED.
 
                                                                   June 16, 1998
 
To Brokers, Dealers, Commercial Banks,
  Trust Companies and Other Nominees:
 
    We have been appointed by PPC Acquisition Corp., a Delaware corporation (the
"Offeror") and a direct wholly owned subsidiary of Kluwer Boston, Inc., a
Massachusetts corporation (the "Parent"), to act as Dealer Manager in connection
with the Offeror's offer to purchase all outstanding shares of Common Stock, par
value $.10 per share (the "Shares"), of Plenum Publishing Corporation, a
Delaware corporation (the "Company"), at a purchase price of $73.50 per Share,
net to the seller in cash, without interest thereon, upon the terms and subject
to the conditions set forth in the Offer to Purchase, dated June 16, 1998 (the
"Offer to Purchase"), and in the related Letter of Transmittal (which, together
with any amendments or supplements thereto, constitute the "Offer") enclosed
herewith. The Offer is being made pursuant to the Agreement and Plan of Merger,
dated as of June 10, 1998 (the "Merger Agreement"), by and among the Parent, the
Offeror and the Company.
 
    The Offer is conditioned upon, among other things, there being validly
tendered by the Expiration Date (as defined in the Offer to Purchase) and not
withdrawn that number of Shares which, together with the Shares to be acquired
pursuant to the Purchase Agreements (as defined below) simultaneously with the
acceptance of the Shares pursuant to the Offer, represent at least that number
of shares which would constitute a majority of the Shares outstanding on a fully
diluted basis (the "Minimum Condition"), the Offeror obtaining certain
governmental approvals and the satisfaction of certain other terms and
conditions. In connection with entering into the Merger Agreement, the Offeror
has entered into five Stock Purchase Agreements, each dated as of June 10, 1998
(the "Purchase Agreements"), with the stockholders identified therein (each a
"Stockholder" and collectively, the "Stockholders") beneficially owning an
aggregate of 536,960 Shares representing approximately 15.3% of the outstanding
Shares on a fully diluted basis (the "Stockholders' Shares") pursuant to which
the Stockholders have, among other things, (i) agreed to tender into the Offer,
all of the Stockholders' Shares and not withdraw any of the Stockholders' Shares
unless an election is made by the Offeror to purchase the Stockholders' Shares
and (ii) granted to the Offeror an option to purchase the Stockholders' Shares
exercisable in certain limited circumstances following the Expiration
<PAGE>
Date or the termination of the Offer by the Offeror. In addition, the
Stockholders have agreed to appoint the Offeror under certain circumstances as
such Stockholders' proxy to vote such Stockholders' Shares on all matters in
connection with the consummation of the transactions contemplated by the Merger
Agreement and the Purchase Agreements. The tender by the Stockholders of the
Stockholders' Shares alone will not cause the Minimum Condition to be satisfied.
 
    For your information and for forwarding to your clients for whom you hold
Shares registered in your name or in the name of your nominee, or who hold
Shares registered in their own names, we are enclosing the following documents:
 
    1. The Offer to Purchase dated June 16, 1998;
 
    2. The Letter of Transmittal to tender the Shares for your use and for the
information of your clients (manually signed facsimile copies of the Letter of
Transmittal may be used to tender such Shares);
 
    3. A Notice of Guaranteed Delivery to be used to accept the Offer if
certificates for Shares are not immediately available or time will not permit
certificates for Shares and all other required documents to reach Morgan
Guaranty Trust Company of New York (the "Depositary") by the Expiration Date or
if the procedures for book-entry transfer cannot be completed on a timely basis;
 
    4. A letter from the President and Chief Executive Officer and Chairman of
the Board of the Company and the Company's Solicitation/Recommendation Statement
on Schedule 14D-9 filed with the Securities and Exchange Commission;
 
    5. A form of letter which may be sent to your clients for whose accounts you
hold Shares in your name or in the name of a nominee, with space provided for
obtaining such clients' instructions with regard to the Offer;
 
    6. Guidelines of the Internal Revenue Service for Certification of Taxpayer
Identification Number on Substitute Form W-9; and
 
    8. A return envelope addressed to the Depositary.
 
    YOUR PROMPT ACTION IS REQUESTED. WE URGE YOU TO CONTACT YOUR CLIENTS AS
PROMPTLY AS POSSIBLE. THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00
MIDNIGHT, NEW YORK CITY TIME, ON WEDNESDAY, JULY 15, 1998, UNLESS THE OFFER IS
EXTENDED.
 
    Upon the terms and subject to the conditions of the Offer (including, if the
Offer is extended or amended, the terms and conditions of any such extensions or
amendments), the Offeror will be deemed to have accepted for payment (and
thereby purchased) all Shares validly tendered on or prior to the Expiration
Date and not properly withdrawn if, as and when the Offeror gives oral or
written notice to the Depositary of the Offeror's acceptance of such Shares for
payment pursuant to the Offer. Payment for Shares purchased pursuant to the
Offer will in all cases be made only after timely receipt by the Depositary of
(i) certificates for such Shares, or timely confirmation of a book-entry
transfer of such Shares into the Depositary's account at The Depository Trust
Company, pursuant to the procedures described in Section 3- "Procedures for
Tendering Shares" of the Offer to Purchase and (ii) the Letter of Transmittal
(or manually signed facsimile thereof), properly completed and duly executed
with all required signature guarantees or an Agent's Message (as defined in the
Offer to Purchase) in connection with a book-entry transfer of Shares, together
with any other documents required by the Letter of Transmittal.
 
    In order to take advantage of the Offer, the Letter of Transmittal (or
manually signed facsimile thereof) duly executed and properly completed with any
required signature guarantees or an Agent's Message in connection with a
book-entry transfer of Shares, and any other required documents, should be sent
to the Depositary, and certificates representing the tendered Shares should be
delivered, all in accordance with the instructions set forth in the Letter of
Transmittal and the Offer to Purchase.
 
                                       2
<PAGE>
    If holders of Shares wish to tender their Shares, but it is impracticable
for them to tender their certificates on or prior to the Expiration Date or to
comply with the book-entry transfer procedures on a timely basis, a tender may
be effected by following the guaranteed delivery procedures specified in Section
3- "Procedures for Tendering Shares" of the Offer to Purchase.
 
    Neither the Parent nor the Offeror nor any officer, director, stockholder,
agent or other representative of the Parent or the Offeror will pay any fees or
commissions to any broker, dealer, or other person (other than the Dealer
Manager, the Information Agent and the Depositary as described in the Offer to
Purchase) in connection with the solicitation of tenders of Shares pursuant to
the Offer. The Offeror will, however, upon request, reimburse brokers, dealers,
commercial banks and trust companies and other nominees for reasonable and
necessary costs and expenses incurred by them in forwarding the Offer to
Purchase and the related documents to the beneficial owners of Shares held by
them as nominee or in a fiduciary capacity.
 
    The Offeror will pay or cause to be paid all stock transfer taxes applicable
to the purchase of Shares pursuant to the Offer, except as set forth in
Instruction 7 of the Letter of Transmittal.
 
    Any inquiries you have with respect to the Offer should be addressed to
Credit Suisse First Boston Corporation, the Dealer Manager, or Georgeson &
Company Inc., the Information Agent, at their respective addresses and telephone
numbers set forth on the back cover of the Offer to Purchase. Additional copies
of the enclosed material may be obtained from the Information Agent or the
Dealer Manager or from brokers, dealers, commercial banks or trust companies.
 
                                      Very truly yours,
 
                                      CREDIT SUISSE FIRST BOSTON CORPORATION
 
    NOTHING HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL CONSTITUTE YOU OR ANY
OTHER PERSON AS THE AGENT OF THE OFFEROR, THE PARENT, THE COMPANY, THE DEALER
MANAGER, THE DEPOSITARY, THE INFORMATION AGENT OR OF ANY AFFILIATE OF ANY OF
THEM, OR AUTHORIZE YOU OR ANY OTHER PERSON TO USE ANY DOCUMENT OR MAKE ANY
STATEMENTS ON BEHALF OF ANY OF THEM IN CONNECTION WITH THE OFFER, EXCEPT FOR
STATEMENTS EXPRESSLY MADE IN THE OFFER TO PURCHASE OR THE LETTER OF TRANSMITTAL.
 
                                       3

<PAGE>
                           Offer to Purchase for Cash
 
                           All Outstanding Shares of
 
                                  Common Stock
 
                                       of
 
                         Plenum Publishing Corporation
 
                                       at
 
                              $73.50 Net Per Share
 
                                       by
 
                             PPC Acquisition Corp.
 
                      a direct wholly owned subsidiary of
 
                              Kluwer Boston, Inc.
 
  THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
        TIME ON WEDNESDAY, JULY 15, 1998, UNLESS THE OFFER IS EXTENDED.
 
                                                                   June 16, 1998
 
To Our Clients:
 
    Enclosed for your consideration is an Offer to Purchase, dated June 16, 1998
(the "Offer to Purchase"), and the related Letter of Transmittal (which,
together with any amendments or supplements thereto, constitute the "Offer"), in
connection with the offer by PPC Acquisition Corp., a Delaware corporation (the
"Offeror") and a direct wholly owned subsidiary of Kluwer Boston, Inc., a
Massachusetts corporation (the "Parent"), to purchase all outstanding shares of
Common Stock par value $.10 per share (the "Shares"), of Plenum Publishing
Corporation, a Delaware corporation (the "Company"), at a purchase price of
$73.50 per Share net to the seller in cash, without interest thereon, upon the
terms and subject to the conditions set forth in the Offer.
 
    We are the holder of record of Shares held by us for your account. A tender
of such Shares can be made only by us as the holder of record and pursuant to
your instructions. The Letter of Transmittal is furnished to you for your
information only and cannot be used by you to tender Shares held by us for your
account.
 
    We request instructions as to whether you wish to have us tender on your
behalf any or all of the Shares held by us for your account, upon the terms and
subject to the conditions set forth in the Offer.
 
    Your attention is directed to the following:
 
    1. The offer price is $73.50 per Share net to the seller in cash, without
interest thereon, upon the terms and subject to the conditions set forth in the
Offer.
 
    2. The Offer is being made pursuant to the Agreement and Plan of Merger,
dated as of June 10, 1998, by and among the Parent, the Offeror and the Company
(the "Merger Agreement").
 
    3. The Offer and withdrawal rights will expire at 12:00 Midnight, New York
City time, on July 15, 1998, unless the Offer is extended.
 
    4. The Board of Directors of the Company has unanimously approved the Merger
Agreement, the Offer and the Merger (as defined in the Offer to Purchase), has
unanimously determined that the Offer and the Merger are fair to, and in the
best interests of, the Company's stockholders and recommends that the Company's
stockholders accept the Offer and tender their Shares pursuant to the Offer.
 
    5. The Offer is being made for all Shares outstanding. The Offer is
conditioned upon, among other things, there being validly tendered by the
Expiration Date (as defined in the Offer to Purchase) and not withdrawn
<PAGE>
that number of Shares which together with the Shares to be acquired pursuant to
the Purchase Agreements (as defined below) simultaneously with the acceptance of
the Shares pursuant to the Offer, represent at least that number of Shares which
would constitute a majority of the Shares outstanding on a fully diluted basis
(the "Minimum Condition"), the Offeror obtaining certain governmental approvals
and the satisfaction of certain other terms and conditions. In connection with
entering into the Merger Agreement, the Offeror has entered into five Stock
Purchase Agreements, each dated as of June 10, 1998 (the "Purchase Agreements"),
with the stockholders identified therein (each a "Stockholder" and collectively,
the "Stockholders") beneficially owning an aggregate of 536,960 Shares
representing approximately 15.3% of the outstanding Shares, on a fully diluted
basis (the "Stockholders' Shares") pursuant to which the Stockholders have,
among other things (i) agreed to tender into the Offer all of the Stockholders'
Shares and not withdraw any of the Stockholders' Shares unless an election is
made by the Offeror to purchase the Stockholders' Shares and (ii) granted to the
Offeror an option to purchase the Stockholders' Shares exercisable in certain
limited circumstances following the Expiration Date or the termination of the
Offer by the Offeror. In addition, the Stockholders have agreed to appoint the
Offeror under certain circumstances as such Stockholders' proxy to vote such
Stockholders' Shares on all matters in connection with the consummation of the
transactions contemplated by the Merger Agreement and the Purchase Agreements.
The tender by the Stockholders of the Stockholders' Shares alone will not cause
the Minimum Condition to be satisfied.
 
    6. Except as set forth in Instruction 7 of the Letter of Transmittal,
tendering stockholders will not be obligated to pay stock transfer taxes on the
purchase of Shares by the Offeror pursuant to the Offer. However, federal income
tax backup withholding at a rate of 31% may be required, unless an exemption is
provided or unless the required taxpayer identification information is provided
(see Instruction 9 to the Letter of Transmittal).
 
    7. Notwithstanding any other provision of the Offer, payment for Shares
purchased pursuant to the Offer will in all cases be made only after timely
receipt by the Depositary of (i) certificates for such Shares, or timely
confirmation of a book-entry transfer of such shares into the Depositary's
account at The Depositary Trust Company, pursuant to the procedures described in
Section 3-"Procedures for Tendering Shares" of the Offer to Purchase and (ii)
the Letter of Transmittal (or manually signed facsimile thereof) properly
completed and duly executed with all required signature guarantees, or an
Agent's Message (as defined in the Offer to Purchase) in connection with a
book-entry transfer of Shares, together with any other documents required by the
Letter of Transmittal. Accordingly, payment may not be made to all tendering
stockholders at the same time depending upon when certificates representing
Shares or confirmations for book-entry transfer of such Shares into the
Depositary's account are actually received by the Depositary.
 
    If you wish to have us tender any or all of your Shares, please so instruct
us by completing, executing and returning to us the instruction form contained
in this letter. An envelope in which to return your instructions to us is
enclosed. If you authorize the tender of your Shares, all such Shares will be
tendered unless otherwise specified in your instructions. Your instructions
should be forwarded to us in ample time to permit us to submit a tender on your
behalf prior to the Expiration Date.
 
    The Offer is made solely by the Offer to Purchase and the related Letter of
Transmittal and is being made to all holders of Shares. The Offeror is not aware
of any jurisdiction in which the making of the Offer or the tender of Shares in
connection therewith would not be in compliance with applicable law. If the
Parent or the Offeror becomes aware of any jurisdiction in which the making of
the Offer or the tender of Shares in connection therewith would not be in
compliance with applicable law, the Parent or the Offeror will make a good faith
effort to comply with any such law. If, after such good faith effort, the Parent
or the Offeror cannot comply with any such law, the Offer will not be made to
(nor will tenders be accepted from or on behalf of) the holders of Shares
residing in any such jurisdiction. In any jurisdiction where the securities,
blue sky or other laws require the Offer to be made by licensed brokers or
dealers, the Offer shall be deemed to be made on behalf of the Parent or the
Offeror by the Dealer Manager (as defined in the Offer to Purchase) or one or
more registered brokers or dealers licensed under the laws of such jurisdiction.
 
                                       2
<PAGE>
               INSTRUCTIONS WITH RESPECT TO THE OFFER TO PURCHASE
                FOR CASH ALL OUTSTANDING SHARES OF COMMON STOCK
 
                        OF PLENUM PUBLISHING CORPORATION
 
    The undersigned acknowledges receipt of your letter and the enclosed Offer
to Purchase, dated June 16, 1998 and the related Letter of Transmittal (which,
together with any amendments or supplements thereto, constitute the "Offer"), in
connection with the offer by PPC Acquisition Corp., a Delaware corporation and a
direct wholly owned subsidiary of Kluwer Boston, Inc., a Massachusetts
corporation, to purchase all outstanding shares of Common Stock, par value $.10
per share ("Shares"), of Plenum Publishing Corporation, a Delaware corporation,
at a purchase price of $73.50 per Share net to the seller in cash, without
interest thereon, upon the terms and subject to the conditions set forth in the
Offer.
 
    This will instruct you to instruct your nominee to tender the number of
Shares indicated below (or, if no number is indicated below, all Shares) that
are held for the account of the undersigned, upon the terms and subject to the
conditions set forth in the Offer.
 
                                                  SIGN HERE
 
                        Number of Shares to be Tendered*
- ----------------------------------------
                      ____________ shares of Common Stock
- ----------------------------------------
Signature(s)
 
                                                               -----------------
 
Dated: June 16, 1998
- ---------------------------------------------------
                                                               Please Type or
Print Name(s)
 
                                                               -----------------
- ---------------------------------------------------
                                                               Please Type or
Print Address(es)
 
                                                               -----------------
                                                               Area Code and
Telephone Number
 
                                                               -----------------
                                                               Taxpayer
Identification or
                                                               Social Security
Number
 
- ------------------------------
 
*   Unless otherwise indicated, it will be assumed that all your Shares held by
    us for your account are to be tendered.
 
                                       3

<PAGE>
                           Offer to Purchase for Cash
 
                           All Outstanding Shares of
 
                                  Common Stock
 
                                       of
 
                         Plenum Publishing Corporation
 
                                       at
 
                              $73.50 Net Per Share
 
                                       by
 
                             PPC Acquisition Corp.
 
                        a direct wholly owned subsidiary
 
                                       of
 
                              Kluwer Boston, Inc.
 
  THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
        TIME ON WEDNESDAY, JULY 15, 1998, UNLESS THE OFFER IS EXTENDED.
 
                                                                   June 16, 1998
 
To the Participants in the Profit Sharing Plan of Plenum Publishing Corporation:
 
    Enclosed for your consideration is an Offer to Purchase, dated June 16, 1998
(the "Offer to Purchase"), and the related Letter of Transmittal (which,
together with any amendments or supplements thereto, constitute the "Offer"), in
connection with the offer by PPC Acquisition Corp., a Delaware corporation (the
"Offeror") and a direct wholly owned subsidiary of Kluwer Boston, Inc., a
Massachusetts corporation (the "Parent"), to purchase all of the outstanding
shares of Common Stock, par value $.10 per share (the "Shares"), of Plenum
Publishing Corporation, a Delaware corporation (the "Company"), at a purchase
price of $73.50 per Share net to the seller in cash, without interest thereon,
upon the terms and subject to the conditions set forth in the Offer. We have
been designated by the Company pursuant to authority granted to it under Section
2.4(g) of the Trust Agreement between the Company and The Dreyfus Trust Company
(the "Trustee") dated as of March 16, 1992 to notify you of the Offer and
distribute the information, materials and directions relating to the Offer.
 
    As a participant in the Company's Profit Sharing Plan, you may direct the
Trustee to tender Shares allocated to your Profit Sharing Plan account. The
Trustee is the holder of record of Shares held by the Trustee for your account.
A tender of such Shares can be made only by the Trustee as the holder of record
and pursuant to your instructions. The Letter of Transmittal is furnished to you
for your information only and cannot be used by you to tender Shares held by the
Trustee for your account.
 
    We request instructions as to whether you wish to instruct the Trustee to
tender on your behalf any or all of the Shares held by the Trustee for your
account, upon the terms and subject to the conditions set forth in the Offer.
 
    Your attention is directed to the following:
 
    1. The offer price is $73.50 per Share net to the seller in cash, without
interest thereon, upon the terms and subject to the conditions set forth in the
Offer.
 
    2. The Offer is being made pursuant to the Agreement and Plan of Merger,
dated as of June 10, 1998, by and among the Parent, the Offeror and the Company
(the "Merger Agreement").
 
    3. The Offer and withdrawal rights will expire at 12:00 Midnight, New York
City time, on July 15, 1998, unless the Offer is extended.
<PAGE>
    4. The Board of Directors of the Company has unanimously approved the Merger
Agreement, the Offer and the Merger (as defined in the Offer to Purchase), has
unanimously determined that the Offer and the Merger are fair to, and in the
best interests of the Company's stockholders and recommends that stockholders
accept the Offer and tender their Shares.
 
    5. The Offer is being made for all Shares outstanding. The Offer is
conditioned upon, among other things, there being validly tendered by the
Expiration Date (as defined in the Offer to Purchase) and not withdrawn that
number of Shares which would, together with the Shares beneficially owned by the
Parent or the Offeror constitute at least that number of Shares which would
constitute a majority of the outstanding Shares on a fully diluted basis (the
"Minimum Condition"). In connection with entering into the Merger Agreement, the
Offeror has entered into five separate Stock Purchase Agreements, each dated as
of June 10, 1998 (the "Purchase Agreements") with the stockholders identified
therein (each a "Stockholder" and collectively, the "Stockholders") beneficially
owning an aggregate of 536,960 Shares (including 117,540 Shares which are held
in the Profit Sharing Plan for the benefit of two of such Stockholders)
representing approximately 15.3% of the Shares outstanding, on a fully diluted
basis (the "Stockholders' Shares"), pursuant to which the Stockholders have,
among other things (i) agreed to tender into the Offer all of the Stockholders'
Shares and not to withdraw any of the Stockholders' Shares unless an election is
made by the Offeror to purchase the Stockholders' Shares and (ii) granted to the
Offeror an option to purchase the Stockholders' Shares exercisable in certain
limited circumstances following the Expiration Date or the termination of the
Offer by the Offeror. In addition, the Stockholders have agreed to appoint the
Offeror under certain circumstances as such Stockholders' proxy to vote such
Stockholders' Shares on all matters in connection with the consummation of the
transactions contemplated by the Merger Agreement, the Purchase Agreements and
the Option Agreement. The tender by the Stockholders of the Stockholders' Shares
alone will not cause the Minimum Condition to be satisfied.
 
    6. The Letter of Transmittal referred to above and in the Offer to Purchase
cannot be used by you to tender the Shares held in your Profit Sharing Plan
account. The enclosed Election Form for the Profit Sharing Plan is a substitute
for the Letter of Transmittal and must be used by you to direct the Trustee to
tender Shares in your Profit Sharing Plan account.
 
    7. If you wish to have the Trustee tender any or all of your Shares, please
so instruct the Trustee by completing, executing and returning to the Trustee
the Election Form contained in this letter. An envelope in which to return your
instructions to the Trustee is enclosed. If you authorize the tender of your
Shares, all such Shares will be tendered unless otherwise specified in your
instructions. Your Election Form should be forwarded to the Trustee in ample
time to permit the Trustee to submit a tender on your behalf prior to the
Expiration Date (as defined in the offer to purchase). Under the Profit Sharing
Plan, you may direct the Trustee to tender all or part of the Shares that are
allocated to your account.
 
    8. If you direct the Trustee to tender Shares allocated to your account in
the Profit Sharing Plan, proceeds from the sale of the Shares shall be credited
to each account from which the Shares were taken. In accordance with the Profit
Sharing Plan's investment transfer provisions, you will be able to transfer
amounts from the account from which the Shares were taken to the Profit Sharing
Plan's other investment funds.
 
    9. As more fully described in Section 4 of the Offer to Purchase, tenders
will be deemed irrevocable unless withdrawn by the dates specified therein. If
you instruct the Trustee to tender Shares, and you subsequently decide to change
your instructions, you may do so by sending a notice of withdrawal to the
Trustee. The notice of withdrawal will be effective only if it is in writing and
is received by the Trustee at or before the Expiration Date (as defined in the
Offer to Purchase), at the address set forth on the enclosed return envelope.
Any notice of change of instruction to the Trustee must specify your name, your
social security number, the number of Shares tendered, and the number of Shares
to be withdrawn. Upon receipt of a timely written notice of change of
instruction to the Trustee, previous instructions to tender with respect to such
Shares will be deemed cancelled. If you later wish to re-tender Shares, you may
call Georgeson & Company Inc., the Information Agent at (800) 223-2064 to obtain
a new Election Form. Any new Election Form must be received by the Trustee in
ample time to permit the Trustee to submit a tender on your behalf prior to the
Expiration Date.
 
                                          Kluwer Boston, Inc.
 
                                       2
<PAGE>
              ELECTION FORM WITH RESPECT TO THE OFFER TO PURCHASE
                FOR CASH ALL OUTSTANDING SHARES OF COMMON STOCK
 
                        OF PLENUM PUBLISHING CORPORATION
 
    The undersigned acknowledges receipt of your letter and the enclosed Offer
to Purchase, dated June 16, 1998 and the related Letter of Transmittal (which,
together with any amendments or supplements thereto, constitute the "Offer") in
connection with the offer by PPC Acquisition Corp., a Delaware corporation and a
direct wholly owned subsidiary of Kluwer Boston, Inc., a Massachusetts
corporation, to purchase all outstanding shares of Common Stock, par value $.10
per share ("Shares"), of Plenum Publishing Corporation, a Delaware corporation,
at a purchase price of $73.50 per Share net to the seller in cash without
interest thereon, upon the terms and subject to the conditions set forth in the
Offer.
 
    This will instruct The Dreyfus Trust Company, as Trustee of the Plenum
Publishing Corporation Profit Sharing Plan, to tender the number of Shares
indicated below (or, if no number is indicated below, all Shares) that are held
for the account of the undersigned, upon the terms and subject to the conditions
set forth in the Offer.
 
                                                  SIGN HERE
 
                        Number of Shares to be Tendered*
- ----------------------------------------
                      ____________ shares of Common Stock
- ----------------------------------------
Signature
 
                                                               -----------------
 
Dated: June 16, 1998
- ---------------------------------------------------
                                                               Please Type or
Print Name
 
                                                               -----------------
- ---------------------------------------------------
                                                               Please Type or
Print Address
 
                                                               -----------------
                                                               Area Code and
Telephone Number
 
                                                               -----------------
                                                               Taxpayer
Identification or
                                                               Social Security
Number
 
- ------------------------------
 
*   Unless otherwise indicated, it will be assumed that all your Shares held by
    The Dreyfus Trust Company for your account are to be tendered.
 
                                       3

<PAGE>
            GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION
                         NUMBER ON SUBSTITUTE FORM W-9
 
    Guidelines for Determining the Proper Identification Number to Give the
Payer.--Social Security numbers have nine digits separated by two hyphens: i.e.
000-00-0000. Employer identification numbers have nine digits separated by only
one hyphen: i.e. 00-0000000. The table below will help determine the number to
give the payer.
<TABLE>
<CAPTION>
- -----------------------------------------------------
                                 Give the TAXPAYER
For this type of account:        IDENTIFICATION
                                 NUMBER of--
- -----------------------------------------------------
<S>        <C>                   <C>
1.         An individual's       The individual
           account
2.         Two or more           The actual owner of
           individuals (joint    the account or, if
           account)              combined funds, the
                                 first individual on
                                 the account(1)
3.         Custodian account of  The minor(2)
           a minor (Uniform
           Gift to Minors Act)
4.         a. The usual          The
              revocable savings  grantor-trustee(1)
              trust (grantor is
              also trustee)
           b. So-called trust
              account that is    The actual owner(1)
              not a legal or
              valid trust under
              state law.
5.         Sole proprietorship   The owner(3)
6.         A valid trust,        The legal entity (Do
           estate, or pension    not furnish the
           trust                 identifying number
                                 of the personal
                                 representative or
                                 trustee unless the
                                 legal entity itself
                                 is not designated in
                                 the account
                                 title.)(4)
- -----------------------------------------------------
 
<CAPTION>
                                 Give the TAXPAYER
For this type of account:        IDENTIFICATION
                                 NUMBER of--
<S>        <C>                   <C>
- -----------------------------------------------------
7.         Corporate account     The corporation
8.         Religious,            The organization
           charitable, or
           educational
           organization account
9.         Partnership account   The partnership
10.        Association, club,    The organization
           or other tax-exempt
           organization
11.        A broker or           The broker or
           registered nominee    nominee
12.        Account with the      The public entity
           Department of
           Agriculture in the
           name of a public
           entity (such as a
           state or local
           government, school
           district, or prison)
           that receives
           agricultural program
           payments
</TABLE>
 
- ---------------------------------------------
- ---------------------------------------------
 
(1) List first and circle the name of the person whose number you furnish. If
    only one person on a joint account has an SSN, that person's number must be
    furnished.
 
(2) Circle the minor's name and furnish the minor's social security number.
 
(3) Show your individual name. You may also enter your business or "doing
    business as" name. You may use either your social security number or your
    employer identification number.
 
(4) List first and circle the name of the legal trust, estate, or pension trust.
 
NOTE: If no name is circled when there is more than one name listed, the number
      will be considered to be that of the first name listed.
<PAGE>
            GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION
                         NUMBER ON SUBSTITUTE FORM W-9
                                     Page 2
 
Note: Section references are to the Internal Revenue Code unless otherwise
      noted.
 
Obtaining a Number
 
If you do not have a taxpayer identification number or you don't know your
number, obtain Form SS-5, Application for a Social Security Number Card (for
individuals), or Form SS-4, Application for Employer Identification Number (for
businesses and all other entities), at the local office of the Social Security
Administration or the Internal Revenue Service (the "IRS") and apply for a
number.
 
Payees and Payments Exempt from Backup Withholding
 
The following is a list of payees exempt from backup withholding and for which
no information reporting is required. For interest and dividends, all listed
payees are exempt except item (9). For broker transactions, payees listed in
items (1) through (13) and a person registered under the Investment Advisors Act
of 1940 who regularly acts as a broker are exempt. Payments subject to reporting
under sections 6041 and 6041A are generally exempt from backup withholding only
if made to payees described in items (1) through (7), except a corporation
(other than certain hospitals described in Regulations section 1.6041-3(c)) that
provides medical and health care services or bills and collects payments for
such services is not exempt from backup withholding or information reporting.
Only payees described in items (1) through (5) are exempt from backup
withholding for barter exchange transactions and patronage dividends.
 
(1) An organization exempt from tax under section 501(a), or an IRA, or a
custodial account under section 403(b)(7), if the account satisfies the
requirements of section 401(f)(2).
 
(2) The United States or any of its agencies or instrumentalities.
 
(3) A state, the District of Columbia, a possession of the United States, or any
of their political subdivisions or instrumentalities.
 
(4) A foreign government or any of its political subdivisions, agencies or
instrumentalities.
 
(5) An international organization or any of its agencies or instrumentalities.
 
(6) A corporation.
 
(7) A foreign central bank of issue.
 
(8) A dealer in securities or commodities required to register in the United
States, the District of Columbia or a possession of the United States.
 
(9) A futures commission merchant registered with the Commodity Futures Trading
Commission.
 
(10) A real estate investment trust.
 
(11) An entity registered at all times during the tax year under the Investment
Company Act of 1940.
 
(12) A common trust fund operated by a bank under section 584(a).
 
(13) A financial institution.
 
(14) A middleman known in the investment community as a nominee or listed in the
most recent publication of the American Society of Corporate Secretaries, Inc.,
Nominee List.
 
(15) A trust exempt from tax under section 664 or described in section 4947.
 
Payments of dividends and patronage dividends that generally are exempt from
backup withholding include the following:
 
- - Payments to nonresident aliens subject to withholding under section 1441.
 
- - Payments to partnerships not engaged in a trade or business in the U.S. and
  which have at least one nonresident alien partner.
 
- - Payments of patronage dividends not paid in money.
 
- - Payments made by certain foreign organizations.
 
- - Section 404(k) payments made by an ESOP.
 
Payments of interest that generally are exempt from backup withholding include
the following:
 
- - Payments of interest on obligations issued by individuals. Note: You may be
  subject to backup withholding if this interest is $600 or more and is paid in
  the course of the payer's trade or business and you have not provided your
  correct taxpayer identification number to the payor.
 
- - Payments of tax-exempt interest (including exempt-interest dividends under
  section 852).
 
- - Payments described in section 6049(b)(5) to non-resident aliens.
 
- - Payments on tax-free covenant bonds under section 1451.
 
- - Payments made by certain foreign organizations.
 
- - Payments of mortgage interest to you.
 
Exempt payees described above should file substitute Form W-9 to avoid possible
erroneous backup withholding. FILE THIS FORM WITH THE PAYER, FURNISH YOUR
TAXPAYER IDENTIFICATION NUMBER, WRITE "EXEMPT" ON THE FACE OF THE FORM, SIGN AND
DATE THE FORM AND RETURN IT TO THE PAYER. IF YOU ARE A NON-RESIDENT ALIEN OR A
FOREIGN ENTITY NOT SUBJECT TO BACKUP WITHHOLDING, FILE WITH PAYER A COMPLETED
INTERNAL REVENUE FORM W-8 (CERTIFICATE OF FOREIGN STATUS).
 
    Payments that are not subject to information reporting are also not subject
to backup withholding. For details, see sections 6041, 6041A, 6042, 6044, 6045,
6049, 6050A and 6050N and the regulations promulgated thereunder.
 
Privacy Act Notice.--Section 6109 requires most recipients of dividend,
interest, or other payments to give taxpayer identification numbers to payors
who must report the payments to the IRS. The IRS uses the numbers for
identification purposes. Payers must generally withhold 31% of taxable interest,
dividend, and certain other payments to a payee who does not furnish a taxpayer
identification number to a payer. Certain penalties may also apply.
 
Penalties
 
(1) Penalty for Failure to Furnish Taxpayer Identification Number.--If you fail
to furnish your correct taxpayer identification number to a requester, you are
subject to a penalty of $50 for each such failure unless your failure is due to
reasonable cause and not to willful neglect.
 
(2) Civil Penalty for False Information With Respect to Withholding.--If you
make a false statement with no reasonable basis which results in no imposition
of backup withholding, you are subject to a penalty of $500.
 
(3) Criminal Penalty for Falsifying Information.--Willfully falsifying
certifications or affirmations may subject you to criminal penalties including
fines and/or imprisonment.
 
FOR ADDITIONAL INFORMATION CONTACT YOUR TAX CONSULTANT OR THE INTERNAL REVENUE
SERVICE.

<PAGE>

                                                                Exhibit 99(a)(8)


This announcement is neither an offer to purchase nor a solicitation of an offer
to sell Shares. The Offer is made solely by the Offer to Purchase dated June 16,
1998 and the related Letter of Transmittal and any amendments or supplements
thereto, and is being made to all holders of Shares. The Offer is not being made
to, nor will tenders be accepted from or on behalf of, holders of Shares in any
jurisdiction where the making of the Offer or acceptance thereof is not in
compliance with the laws of such jurisdiction. In those jurisdictions where
securities, blue sky or other laws require the Offer to be made by a licensed
broker or dealer, the Offer shall be deemed to be made on behalf of the Offeror
by Credit Suisse First Boston Corporation ("Credit Suisse First Boston") or one
or more registered brokers or dealers licensed under the laws of such
jurisdiction.

                        NOTICE OF OFFER TO PURCHASE FOR CASH
                       ALL OUTSTANDING SHARES OF COMMON STOCK
                                         OF
                           PLENUM PUBLISHING CORPORATION
                                         AT
                                $73.50 NET PER SHARE
                                         BY
                                          
                               PPC ACQUISITION CORP.
                        A DIRECT WHOLLY OWNED SUBSIDIARY OF
                                KLUWER BOSTON, INC.

     PPC Acquisition Corp., a Delaware corporation (the "Offeror") and a direct
wholly owned subsidiary of Kluwer Boston, Inc., a Massachusetts corporation
("Parent"), is offering to purchase all of the outstanding shares of Common
Stock, par value $.10 per share (the "Shares"), of Plenum Publishing
Corporation, a Delaware corporation (the "Company"), at a purchase price of
$73.50 per Share, net to the seller in cash, without interest thereon, upon the
terms and subject to the conditions set forth in the Offer to Purchase dated
June 16, 1998 (the "Offer to Purchase") and in the related Letter of Transmittal
(which, together with any amendments or supplements thereto, constitute the
"Offer"). Tendering stockholders who have shares registered in their name and
who tender directly will not be charged brokerage fees or commissions or,
subject to Instruction 7 of the Letter of Transmittal, transfer taxes on the
purchase of Shares pursuant to the Offer. Following the Offer, the Offeror
intends to effect the Merger described below.

   ---------------------------------------------------------------------------
      THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK
       CITY TIME, ON WEDNESDAY, JULY 15, 1998, UNLESS THE OFFER IS EXTENDED.
   ---------------------------------------------------------------------------

     THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS, THERE BEING VALIDLY
TENDERED BY THE EXPIRATION DATE (AS DEFINED BELOW) AND NOT WITHDRAWN THAT NUMBER
OF SHARES WHICH, TOGETHER WITH THE SHARES TO BE ACQUIRED PURSUANT TO THE
PURCHASE AGREEMENTS (AS DEFINED BELOW) SIMULTANEOUSLY WITH THE ACCEPTANCE OF
SHARES PURSUANT TO THE OFFER, REPRESENT AT LEAST THAT NUMBER OF SHARES WHICH
WOULD CONSTITUTE A MAJORITY OF THE SHARES OUTSTANDING ON A FULLY DILUTED BASIS
(THE "MINIMUM CONDITION"), THE OFFEROR OBTAINING CERTAIN GOVERNMENTAL APPROVALS
AND THE SATISFACTION OF CERTAIN OTHER TERMS AND CONDITIONS. SEE THE
INTRODUCTION, SECTION 1-"TERMS OF THE OFFER" AND SECTION 14-"CERTAIN CONDITIONS
TO THE OFFEROR'S OBLIGATIONS" OF THE OFFER TO PURCHASE.

     The Offer is being made pursuant to the Agreement and Plan of Merger, dated
as of June 10, 1998 (the "Merger Agreement"), by and among Parent, the Offeror
and the Company. Pursuant to the Merger Agreement, and on the terms and subject
to the conditions set forth therein, the Offeror will be merged with and into
the Company (the "Merger"), with the Company to be the surviving corporation in
the Merger, and each outstanding Share (other than any Shares held by Parent,
the Offeror, any wholly owned subsidiary of Parent or the Offeror, or in the
treasury of the Company which shall be cancelled, and Shares held by
stockholders who properly exercise appraisal rights under Delaware law, if any),
will be converted into the right to receive $73.50 in cash, without interest
thereon, and the Company will become a direct wholly owned subsidiary of Parent.

     THE BOARD OF DIRECTORS OF THE COMPANY HAS UNANIMOUSLY APPROVED THE MERGER
AGREEMENT, THE OFFER AND THE MERGER, HAS UNANIMOUSLY DETERMINED THAT THE OFFER
AND THE MERGER ARE FAIR TO, AND IN THE BEST INTERESTS OF, THE COMPANY'S
STOCKHOLDERS AND RECOMMENDS THAT THE COMPANY'S STOCKHOLDERS ACCEPT THE OFFER AND
TENDER THEIR SHARES PURSUANT TO THE OFFER.

     The Offeror has entered into five Stock Purchase Agreements, each dated as
of June 10, 1998 (the "Purchase Agreements"), with the stockholders identified
therein (each a "Stockholder" and collectively, the "Stockholders") beneficially
owning an aggregate of 536,960 Shares representing approximately 15.3% of the
outstanding Shares on a fully diluted basis (the "Stockholders' Shares")
pursuant to which the Stockholders have, among other things, (i) agreed to
tender into the Offer all of the Stockholders' Shares and not withdraw any of
the Stockholders' Shares unless an election is made by the Offeror to purchase
the Stockholders' Shares and (ii) granted to the Offeror an option to purchase
the Stockholders' Shares exercisable in certain limited circumstances following
the Expiration Date or the termination of the Offer by the Offeror). In
addition, the Stockholders have agreed to appoint the Offeror under certain
circumstances as such Stockholders' proxy to vote such Stockholders' Shares on
all matters in connection with the consummation of the transactions contemplated
by the Merger Agreement and the Purchase Agreements. THE TENDER BY THE
STOCKHOLDERS OF THE STOCKHOLDERS' SHARES ALONE WILL NOT CAUSE THE MINIMUM
CONDITION TO BE SATISFIED.

     For purposes of the Offer, the Offeror shall be deemed to have accepted for
payment (and thereby purchased) validly tendered Shares, if, as and when the
Offeror gives oral or written notice to Morgan Guaranty Trust Company of New
York (the "Depositary") of the Offeror's acceptance of such Shares for payment
pursuant to the Offer. In all cases, payment for Shares accepted for payment
pursuant to the Offer will be made by deposit of the purchase price therefor
with the Depositary, which will act as agent for tendering stockholders for the
purpose of receiving payment from the Offeror and transmitting payment to
tendering stockholders. Under no circumstances will interest on the purchase
price of the Shares be paid by the Offeror by reason of any delay in making
payment. Payment for Shares purchased pursuant to the Offer will in all cases be
made only after timely receipt by the Depositary of (i) certificates for such
Shares (or timely confirmation of a book-entry transfer of such Shares into the
Depositary's account at the Book-Entry Transfer Facility (as defined in the
Offer to Purchase)), and (ii) the Letter of Transmittal (or manually signed
facsimile thereof) properly completed and duly executed with all required
signature guarantees or an Agent's Message (as defined in the Offer to Purchase)
in connection with a book-entry transfer of Shares, together with any other
documents required by the Letter of Transmittal.

     The Offeror expressly reserves the right at any time or from time to time,
subject to the terms of the Merger Agreement and regardless of whether any of
the events set forth in Section 14 -"Certain Conditions to the Offeror's
Obligations" of the Offer to Purchase shall have occurred or shall have been
determined by the Offeror to have occurred, to extend the period of time during
which the Offer is open and thereby delay acceptance for payment of, and the
payment for, any Shares by giving oral or written notice of such extension to
the Depositary. Any such extension will be followed as promptly as practicable
by public announcement thereof no later than 9:00 a.m., New York City time, on
the next business day after the previously scheduled Expiration Date.

     The term "Expiration Date" means 12:00 Midnight, New York City time, on
July 15, 1998 unless and until the Offeror shall have extended the period of
time for which the Offer is open, in which event the term "Expiration Date"
shall mean the latest time and date at which the Offer, as so extended by the
Offeror, shall expire.

     Tenders of Shares made pursuant to the Offer are irrevocable, provided that
Shares tendered pursuant to the Offer may be withdrawn at any time prior to the
Expiration Date and, unless theretofore accepted for payment by the Offeror
pursuant to the Offer, may also be withdrawn at any time after August 14, 1998.
To be effective, a written or facsimile transmission notice of withdrawal must
be timely received by the Depositary at the address set forth on the back cover
page of the Offer to Purchase and must specify the name of the person who
tendered the Shares to be withdrawn, the number of Shares to be withdrawn and
the name of the registered holders, if different from the name of the person who
tendered such Shares. If certificates for Shares to be withdrawn have been
delivered or otherwise identified to the Depositary, then, prior to the release
of such certificates, the serial numbers of the particular certificates
evidencing such Shares and a signed notice of withdrawal with signatures
guaranteed by an Eligible Institution (as defined in the Offer to Purchase) must
be submitted prior to the release of such Shares (except that such signature
guarantee requirement is not applicable in the case of Shares tendered by an
Eligible Institution). In the case of Shares tendered by book-entry transfer,
the notice of withdrawal must also specify the name and number of the account at
the Book-Entry Transfer Facility to be credited with the withdrawn Shares and
otherwise comply with such Book-Entry Transfer Facility's procedures. Any Shares
properly withdrawn will be deemed not to be validly tendered for purposes of the
Offer. Withdrawn Shares may, however, be retendered by repeating one of the
procedures in Section 3-"Procedure for Tendering Shares" of the Offer to
Purchase at any time before the Expiration Date. All questions as to the form
and the validity (including time of receipt) of notices of withdrawal will be
determined by the Offeror, in its sole discretion, whose determination will be
final and binding. None of the Offeror, Parent, the Dealer Manager, the
Depositary, the Information Agent or any other person will be under any duty to
give notification of any defects or irregularities in any notice of withdrawal
or incur any liability for failure to give any such notification.

     The information required to be disclosed by Rule 14d-6(e)(1)(vii) of the
General Rules and Regulations under the Securities Exchange Act of 1934, as
amended, is contained in the Offer to Purchase and is incorporated herein by
reference.

     The Company has provided to the Offeror its list of stockholders and
security position listings for the purpose of disseminating the Offer to holders
of Shares. The Offer to Purchase and the related Letter of Transmittal and other
related materials will be mailed to record holders of Shares whose names appear
on the Company's stockholder list and will be  furnished to brokers, dealers,
commercial banks, trust companies and similar persons whose names, or the names
of whose nominees, appear on the stockholder list or, if applicable, who are
listed as participants in a clearing agency's security position listing for
subsequent transmittal to beneficial owners of Shares.

     THE OFFER TO PURCHASE AND THE RELATED LETTER OF TRANSMITTAL CONTAIN
IMPORTANT INFORMATION WHICH SHOULD BE READ CAREFULLY BEFORE ANY DECISION IS MADE
WITH RESPECT TO THE OFFER.

     Questions or requests for assistance may be directed to the Information
Agent or to the Dealer Manager at their respective addresses and telephone
numbers set forth below. Additional copies of the Offer to Purchase, the Letter
of Transmittal and other tender offer materials may be obtained from the
Information Agent or the Dealer Manager, and copies will be furnished promptly
at the Offeror's expense. No fees or commissions will be paid to brokers,
dealers or other persons (other than the Information Agent and the Dealer
Manager) for soliciting tenders of Shares pursuant to the Offer.

                      The Information Agent for the Offer is:
                                          
                                     GEORGESON
                                   & COMPANY INC.
                                   --------------
                                          
                                 Wall Street Plaza
                              New York, New York 10005
                         Bankers and Brokers Call Collect:
                                   (212) 440-9800
                             All Others Call Toll Free:
                                   (800) 223-2064
                                          
                        The Dealer Manager for the Offer is:
                                          
                                   CREDIT | FIRST
                                   SUISSE | BOSTON
                                          
                               Eleven Madison Avenue
                           New York, New York 10010-3629
                           Call Toll Free (800) 881-8320


June 16, 1998


<PAGE>

                                                        





June 10, 1998              PRESS RELEASE
For Immediate Release:     For more information, contact:

                      Plenum Publishing Corporation   Wolters Kluwer U.S.
                      Bernard Bressler, Esq.          Mary Dale Walters
                      Secretary and Counsel           Director, Public Relations
                      Phone:  (973) 514-1200          Phone:  (312) 425-7014
                      Fax:  (973) 514-1660            Fax:  (312) 425-0232

                  PLENUM AGREES TO BE ACQUIRED BY WOLTERS KLUWER.
                         TENDER OFFER AT $73.50 TO COMMENCE

New York, N.Y. Plenum Publishing Corporation (NASDAQ:  PLEN) and Wolters Kluwer
N.V., Amsterdam, announced today that they have reached a definitive merger
agreement through which Plenum would be acquired by Wolters Kluwer in a
transaction valued at approximately $258 million.  As previously announced,
Plenum has been exploring the possible sale of the Company.

Under the agreement, Wolters Kluwer will promptly commence a tender offer for
all of the outstanding shares of Plenum common stock at $73.50 per share, net to
the seller in cash.  The tender offer is conditioned on Wolters Kluwer receiving
tenders of at least 51% of Plenum's outstanding common stock and the expiration
of any waiting periods under applicable law.  Shareholders consisting of Martin
Tash, President and CEO, Mark Shaw, Executive Vice President, Ghanshyam Patel,
the Company's Chief Financial Officer and one other director, representing 15.3%
of the outstanding shares of Plenum have entered into a definitive agreement to
sell their shares for the tender price and vote for the merger.

Martin Tash, President and CEO of Plenum, stated that the Board of Directors of
Plenum believes that this transaction constitutes the achievement of a value for
the stockholders of the Company which reflects the accomplishments of the
management and employees of the Company.

Plenum will form an important further addition to Kluwer Academic Publishers,
the wholly owned subsidiary of Wolters Kluwer specializing in research level
scientific publishing.

Jeffrey Smith, President of Kluwer Academic Publishers, stated that the
acquisition of Plenum is an important further step in Wolters Kluwer's expansion
in science publishing.  He added that Plenum's established programs of
high-quality journals, books and databases expand and complement Kluwer
Academic's own programs.  Plenum's journals will also provide important
additional content to Kluwer Academic's web-based electronic publishing system
Kluwer On-Line (http://www.wkap.nl).

<PAGE>

Wolters Kluwer also does business in the USA through its subsidiaries Aspen
Publishers, Gaithersburg, Md.; CCH Incorporated, Riverwoods, Ill.; Legal
Information Services, New York City; Lippincott Raven Publishers, Philadelphia;
Facts & Comparisons, St. Louis; and Blessing/White, Princeton, NJ.

Wolters Kluwer is a multidomestic publishing company active in 26 countries. 
Core activities are legal and tax publishing, business publishing,
medical/scientific publishing, educational publishing/professional training and
trade publishing for select markets.  Wolters Kluwer has a sales level of
approximately Dfl. 5 billion and has some 14,000 employees.  The corporate
website of Wolters Kluwer on the Internet can be accessed at
http://www.wolters-kluwer.com.









<PAGE>

                                                         


                               AGREEMENT AND PLAN

                                       OF

                                     MERGER

                                   ----------

                                  By and Among


                         PLENUM PUBLISHING CORPORATION,


                               KLUWER BOSTON, INC.


                                       and


                              PPC ACQUISITION CORP.



                                  June 10, 1998

<PAGE>

                               TABLE OF CONTENTS

                                                                            Page
                                                                            ----

ARTICLE I   THE OFFER........................................................1
      SECTION 1.1       The Offer............................................1
      SECTION 1.2       Company Action.......................................3
      SECTION 1.3       Directors............................................4

ARTICLE II  THE MERGER.......................................................5
      SECTION 2.1       The Merger...........................................5
      SECTION 2.2       Effective Time; Closing..............................5
      SECTION 2.3       Effects of the Merger; Subsequent Actions............5
      SECTION 2.4       Certificate of Incorporation and By-Laws of
                        the Surviving Corporation............................5
      SECTION 2.5       Directors............................................6
      SECTION 2.6       Officers.............................................6
      SECTION 2.7       Conversion of Shares.................................6
      SECTION 2.8       Conversion of Purchaser Common Stock.................6
      SECTION 2.9       Stockholders' Meeting................................6
      SECTION 2.10      Merger Without Meeting of Stockholders...............7

ARTICLE III DISSENTING SHARES; PAYMENT FOR SHARES............................7
      SECTION 3.1       Dissenting Shares....................................7
      SECTION 3.2       Exchange of Certificates.............................7

ARTICLE IV  REPRESENTATIONS AND WARRANTIES OF THE COMPANY....................9
      SECTION 4.1       Organization and Qualification; Subsidiaries.........9
      SECTION 4.2       Charter and By-laws..................................9
      SECTION 4.3       Capitalization.......................................9
      SECTION 4.4       Authority Relative to this Agreement................10
      SECTION 4.5       No Conflict; Required Filings and Consents..........10
      SECTION 4.6       SEC Reports and Financial Statements................11
      SECTION 4.7       Information.........................................12
      SECTION 4.8       Changes.............................................12
      SECTION 4.9       Opinion of Financial Advisor........................13
      SECTION 4.10      Takeover Statutes...................................13
      SECTION 4.11      Litigation..........................................13
      SECTION 4.12      Employee Plans and Arrangements.....................13
      SECTION 4.13      Assets..............................................15
      SECTION 4.14      Intellectual Property...............................15
      SECTION 4.15      Taxes...............................................16
      SECTION 4.16      Environmental Laws and Regulations..................16
      SECTION 4.17      Insurance...........................................17
      SECTION 4.18      Brokers.............................................17
<PAGE>

ARTICLE V   REPRESENTATIONS AND WARRANTIES OF PARENT
            AND PURCHASER...................................................18
      SECTION 5.1       Organization and Qualification......................18
      SECTION 5.2       Authority Relative to this Agreement and
                        the Stock Purchase Agreements.......................18
      SECTION 5.3       No Conflict; Required Filings and Consents..........18
      SECTION 5.4       Information.........................................19
      SECTION 5.5       Financing...........................................19
      SECTION 5.6       Brokers.............................................19

ARTICLE VI  COVENANTS.......................................................19
      SECTION 6.1       Conduct of Business of the Company..................19
      SECTION 6.2       Access to Information...............................21
      SECTION 6.3       Reasonable Best Efforts.............................22
      SECTION 6.4       Consents............................................22
      SECTION 6.5       Public Announcements................................23
      SECTION 6.6       Indemnification.....................................23
      SECTION 6.7       Notification of Certain Matters.....................24
      SECTION 6.8       No Solicitation.....................................24

ARTICLE VII CONDITIONS TO CONSUMMATION OF THE MERGER........................26
      SECTION 7.1       Conditions to Each Party's Obligation
                        to Consummate the Merger............................26

ARTICLE VIII      TERMINATION; AMENDMENTS; WAIVER...........................26
      SECTION 8.1       Termination.........................................26
      SECTION 8.2       Effect of Termination...............................27
      SECTION 8.3       Fees and Expenses...................................27
      SECTION 8.4       Amendment...........................................28
      SECTION 8.5       Extension; Waiver...................................29

ARTICLE IX  MISCELLANEOUS...................................................29
      SECTION 9.1       Non-Survival of Representations and Warranties......29
      SECTION 9.2       Entire Agreement; Assignment........................29
      SECTION 9.3       Validity............................................29
      SECTION 9.4       Notices.............................................29
      SECTION 9.5       Governing Law.......................................31
      SECTION 9.6       Consent to Jurisdiction; Waiver of Immunities.......31
      SECTION 9.7       Descriptive Headings................................31
      SECTION 9.8       Counterparts........................................31
      SECTION 9.9       Parties in Interest.................................31
      SECTION 9.10      Certain Definitions.................................31
      SECTION 9.11      Specific Performance................................32


                                       ii
<PAGE>

                                LIST OF SCHEDULES


Schedule 4.8            --    Material Changes
Schedule 4.11           --    Litigation
Schedule 4.12(a)        --    Employee Benefit Plans
Schedule 4.12(i)        --    Employment/Termination Agreements
Schedule 4.12(j)        --    Labor Union
Schedule 4.14(b)        --    Licenses
Schedule 4.16           --    Environmental Matters
Schedule 4.17           --    Insurance


                                      iii
<PAGE>

                              LIST OF DEFINED TERMS

                                                                            Page
                                                                            ----

Acquisition Proposal........................................................23
Affiliate...................................................................29
Agreement....................................................................1
Antitrust Laws..............................................................21
Benefit Plans...............................................................12
Board........................................................................1
Certificates.................................................................7
Closing......................................................................5
Closing Date.................................................................5
Code........................................................................12
Commonly Controlled Entity..................................................12
Company......................................................................1
Company Process Agent.......................................................28
Company Representatives.....................................................20
Confidentiality Agreement...................................................27
Consent.....................................................................10
Control.....................................................................29
Dissenting Shares............................................................7
Effective Time...............................................................5
Employee Pension Benefit Plan...............................................12
Employee Welfare Benefit Plan...............................................12
Environmental Claim.........................................................15
Environmental Laws..........................................................16
Environmental Permits.......................................................15
ERISA.......................................................................12
Exchange Act................................................................10
Executive Stock Purchase Agreement...........................................1
GAAP........................................................................11
GCL..........................................................................4
Governmental Entity.........................................................10
HSR Act.....................................................................10
Hazardous Materials.........................................................16
Indemnified Parties.........................................................21
Indemnified Party...........................................................21
Independent Directors........................................................4
Intellectual Property.......................................................14
Lien.........................................................................9
Material Adverse Effect on the Company.......................................8
Material Adverse Effect on Parent...........................................16
Merger.......................................................................4
Minimum Condition............................................................1


                                       iv
<PAGE>

Offer........................................................................1
Offer Documents..............................................................1
Offer to Purchase............................................................1
Other Filings...............................................................11
Parent.......................................................................1
Parent Process Agent........................................................28
Parent Representatives......................................................20
Paying Agent.................................................................7
PBGC........................................................................13
Pension Plan................................................................12
Person......................................................................29
Preferred Stock..............................................................9
Prohibited Transaction......................................................13
Proxy Statement..............................................................6
Purchaser....................................................................1
Purchase Price...............................................................1
Reimbursable Expenses.......................................................26
Reportable Event............................................................13
Schedule 14D-1...............................................................2
Schedule 14D-9...............................................................3
SEC..........................................................................1
SEC Reports.................................................................10
Shares.......................................................................1
Significant Subsidiaries.....................................................8
Superior Proposal...........................................................23
Stockholders' Meeting........................................................6
Subsidiaries................................................................29
Subsidiary..................................................................29
Salomon Smith Barney........................................................12
Surviving Corporation........................................................4
Tax.........................................................................15
Taxes.......................................................................15
Tax Returns.................................................................15
Termination Fee.............................................................26
Violation...................................................................10
Voting Debt..................................................................9
Welfare Plan................................................................12


                                       v
<PAGE>

                          AGREEMENT AND PLAN OF MERGER

      AGREEMENT AND PLAN OF MERGER (this "Agreement"), dated as of June 10,
1998, by and among Kluwer Boston, Inc., a Massachusetts corporation ("Parent"),
PPC Acquisition Corp., a Delaware corporation and subsidiary of Parent
("Purchaser"), and Plenum Publishing Corporation (the "Company"), a Delaware
corporation.

      WHEREAS, the respective Boards of Directors of Parent, Purchaser and the
Company deem it advisable and in the best interests of the stockholders of such
corporations to effect the merger of Purchaser and the Company pursuant to this
Agreement;

      WHEREAS, the respective Boards of Directors of Parent, Purchaser and the
Company have approved the acquisition of the Company by Parent and, in
furtherance of such acquisition, Parent proposes to make or to cause Purchaser
to make a cash tender offer (the "Offer") for all of the outstanding shares of
common stock of the Company, par value $.10 per share (the "Shares"), at a price
of $73.50 net to the seller per Share (the "Purchase Price") on the terms set
forth in the Offer Documents (as such term is defined below), and the Board of
Directors of the Company (the "Board") has unanimously approved the Offer and
resolved to recommend that it be accepted by the stockholders of the Company;

      WHEREAS, certain stockholders of the Company and Parent are entering into
Stock Purchase Agreements, dated as of the date hereof ("Stock Purchase
Agreements"), pursuant to which the Company, and such stockholders will, among
other things, agree to sell Shares to Parent under certain circumstances; and

      WHEREAS, the Company and Parent are entering into an Option Agreement,
dated as of the date hereof ("Option Agreement"), pursuant to which the Company
will grant to Parent an option to acquire an additional 19.9% of its Shares at
the Purchase Price.

      NOW, THEREFORE, in consideration of the foregoing and the respective
representations, warranties, covenants and agreements set forth herein, Parent,
Purchaser and the Company agree as follows:

                                    ARTICLE I

                                    THE OFFER

      SECTION 1.1 The Offer.

      (a) Provided that nothing shall have occurred that would result in the
failure of any of the conditions set forth in Annex I hereto, Parent and
Purchaser shall, as promptly as practicable following the date hereof and in any
event not later than five (5) business days after the public announcement of the
execution hereof, commence their Offer to purchase the Shares at a price equal
to the Purchase Price. The Offer shall be made by means of an offer to purchase
(the "Offer to Purchase" and, together with a letter of transmittal relating
thereto, the "Offer Documents") which shall be subject solely to the condition
that there be validly tendered and not withdrawn prior to the expiration of the
Offer that number of Shares


                                       1
<PAGE>

which, when added to any Shares acquired pursuant to the Stock Purchase
Agreements simultaneously with the acceptance of Shares pursuant to the Offer,
represents at least a majority of the Shares outstanding on a fully diluted
basis (the "Minimum Condition") and to the other conditions set forth in Annex I
hereto (including the expiration of applicable waiting periods under the HSR Act
(as hereinafter defined)). As soon as practicable, Parent and Purchaser shall
file with the Securities and Exchange Commission (the "SEC") a Schedule 14D-1
(which schedule, together with all amendments and supplements thereto, is
hereinafter referred to as the "Schedule 14D-1") with respect to the Offer. The
Company and its counsel shall be given the opportunity to review the Schedule
14D-1 (as defined below) before it is filed with the SEC. In addition, Parent
and Purchaser agree to provide the Company and its counsel with any comments,
whether written or oral, that Parent and/or its counsel may receive from time to
time from the SEC or its staff with respect to the Schedule 14D-1 promptly after
the receipt of such comments or other communications. Without the prior written
consent of the Company, neither Parent nor Purchaser shall decrease the price
per Share or change the form of consideration payable in the Offer, decrease the
number of Shares sought to be purchased in the Offer, change the conditions set
forth in Annex I, impose additional conditions to the Offer or amend any other
term of the Offer in any manner materially adverse to the holders of the Shares.
Subject to the terms of the Offer and this Agreement and the satisfaction or
waiver of all the conditions of the Offer set forth in Annex I hereto as of any
expiration date of the Offer, Parent and/or Purchaser will accept for payment
and pay for all Shares validly tendered and not properly withdrawn pursuant to
the Offer as soon as practicable after such expiration date of the Offer.
Notwithstanding the foregoing, Purchaser may, without the consent of the
Company, (i) extend the Offer on one or more occasions for up to ten business
days for each such extension beyond the then scheduled expiration date (the
initial scheduled expiration date being 20 business days following commencement
of the Offer), if at the then scheduled expiration date of the Offer any of the
conditions to Purchaser's obligation to accept for payment and pay for the
Shares shall not be satisfied or waived, until such time as such conditions are
satisfied or waived, (ii) increase the Purchase Price and extend the Offer for
any period required by any rule, regulation, interpretation or provision of the
SEC or the staff thereof applicable to the Offer and (iii) extend the Offer for
an aggregate period of not more than 10 business days beyond the latest
expiration date that would otherwise be permitted under clause (i) or (ii) of
this sentence if there shall not have been tendered and not withdrawn pursuant
to the Offer at least 90% of the outstanding Shares.

      (b) The Offer Documents will comply in all material respects with the
provisions of applicable federal securities laws and, on the date filed with the
SEC and on the date first published, sent or given to the Company's
stockholders, shall not contain any untrue statement of a material fact or omit
to state any material fact required to be stated therein or necessary in order
to make the statements made therein, in light of the circumstances under which
they were made, not misleading, except that no representation is made by Parent
or Purchaser with respect to information supplied by the Company in writing for
inclusion in the Offer Documents. Each of Parent and Purchaser, on the one hand,
and the Company, on the other hand, agrees to correct promptly any information
provided by it for use in the Offer Documents if and to the extent that it shall
have become false or misleading in any material respect and Parent and Purchaser
further agree to take all steps necessary to cause the Offer Documents as so
corrected to be filed with the SEC and to be disseminated to stockholders of the
Company, in each case as and to the extent required by applicable federal
securities laws.


                                       2
<PAGE>

      SECTION 1.2 Company Action.

      (a) The Company hereby approves of and consents to the Offer and
represents that, at a meeting duly called and held, its Board of Directors has
(i) unanimously determined that this Agreement and the transactions contemplated
hereby and thereby, including, without limitation, the Offer and the Merger, are
fair to and in the best interest of the Company's stockholders, (ii) unanimously
approved this Agreement and the transactions contemplated hereby and thereby,
including, without limitation, the Offer and the Merger and (iii) unanimously
resolved to recommend that the stockholders of the Company accept the Offer,
tender their Shares thereunder to Purchaser and approve and adopt this Agreement
and the Merger; provided, that such recommendation may be withdrawn, modified or
amended if, in the good faith opinion of the Directors, only after receipt of
advice from legal counsel, the failure to withdraw, modify or amend such
recommendation would result in the Board violating its fiduciary duties to the
Company's stockholders under applicable law. The Company consents to the
inclusion of such recommendation and approval in the Offer Documents.

      (b) Contemporaneously with the commencement of the Offer as provided for
in Section 1.1, the Company will file with the SEC a Solicitation/Recommendation
Statement on Schedule 14D-9 (which schedule, together with all amendments and
supplements thereto, is hereafter referred to as the "Schedule 14D-9") which
shall reflect the recommendations and actions of the Company's Board of
Directors referred to above. The Company further agrees to take all steps
necessary to cause the Schedule 14D-9 to be filed with the SEC and to be
disseminated to holders of the Shares, in each case as and to the extent
required by applicable federal securities laws. Each of the Company, on the one
hand, and Parent and Purchaser, on the other hand, agrees to promptly correct
any information provided by it for use in the Schedule 14D-9 if and to the
extent that it shall have become false or misleading in any material respect and
the Company further agrees to take all steps necessary to cause the Schedule
14D-9 as so corrected to be filed with the SEC and to be disseminated to
stockholders of the Company, in each case as and to the extent required by
applicable federal securities laws. Parent and its counsel shall be given the
opportunity to review the Schedule 14D-9 before it is filed with the SEC. In
addition, the Company agrees to provide Parent and its counsel with any
comments, whether written or oral, that the Company and/or its counsel may
receive from time to time from the SEC or its staff with respect to the Schedule
14D-9 promptly after the receipt of such comments or other communications.

      (c) In connection with the Offer, the Company will promptly furnish or
cause to be furnished to Parent and Purchaser mailing labels, security position
listings and any available listing, or computer file containing the names and
addresses of all record holders of the Shares as of a recent date, and shall
furnish Parent and Purchaser with such additional information (including, but
not limited to, updated lists of holders of the Shares and their addresses,
mailing labels and lists of security positions) and assistance as Parent,
Purchaser or their respective agents may reasonably request in communicating the
Offer to the record and beneficial holders of the Shares. Except for such steps
as are necessary to disseminate the Offer Documents, Parent and Purchaser shall
hold in confidence the information contained in any of such labels and lists and
the additional information referred to in the preceding sentence, will use such
information in connection with the Offer, and, if this Agreement is terminated,
will upon request of the Company deliver or cause to be delivered to the Company
all copies of such information then in its possession or the possession of its
agents or representatives.


                                       3
<PAGE>

      SECTION 1.3 Directors.

      (a) Promptly upon the purchase of Shares by Parent or Purchaser or any of
its Subsidiaries pursuant to the Offer and/or pursuant to any of the Stock
Purchase Agreements which represents at least a majority of the outstanding
Shares, Purchaser shall be entitled to designate such number of directors,
rounded up to the next whole number, on the Board of Directors of the Company as
is equal to the product of the total number of directors on such Board (giving
effect to the directors designated by Purchaser pursuant to this sentence)
multiplied by the percentage that the number of Shares so accepted for payment
bears to the total number of Shares then outstanding. In furtherance thereof,
the Company shall, upon request of the Purchaser, use its reasonable best
efforts promptly either to increase the size of its Board of Directors or secure
the resignations of such number of its incumbent directors, or both, as is
necessary to enable Purchaser's designees to be so elected to the Company's
Board of Directors, and shall take all actions available to the Company to cause
Purchaser's designees to be so elected. At such time, the Company shall, if
requested by Purchaser, also cause persons designated by Purchaser to constitute
at least the same percentage (rounded up to the next whole number) as is on the
Company's Board of Directors of (i) each committee of the Company's Board of
Directors, (ii) each board of directors (or similar body) of each Subsidiary of
the Company and (iii) each committee (or similar body) of each such board.

      (b) The Company shall promptly take all actions required pursuant to
Section 14(f) of the Exchange Act and Rule 14f-1 promulgated thereunder in order
to fulfill its obligations under Section 1.3(a), including mailing to
stockholders the information required by such Section 14(f) and Rule 14f-1 as is
necessary to enable Purchaser's designees to be elected to the Company's Board
of Directors. Purchaser or Parent will supply the Company and be solely
responsible for any information with respect to either of them and their
nominees, officers, directors and affiliates required by such Section 14(f) and
Rule 14f-1. The provisions of this Section 1.3 are in addition to and shall not
limit any rights which Purchaser, Parent or any of their affiliates may have as
a holder or beneficial owner of Shares as a matter of law with respect to the
election of directors or otherwise.

      (c) In the event Purchaser's designees are elected to the Company's Board
of Directors, until the Effective Time (as defined below), the Company's Board
shall have at least two directors who are directors on the date hereof
("Independent Directors"), provided that, in such event, if the number of
Independent Directors shall be reduced below two for any reason whatsoever, any
remaining Independent Directors (or Independent Director, if there be only one
remaining) shall be entitled to designate persons to fill such vacancies who
shall be deemed to be Independent Directors for purposes of this Agreement or,
if no Independent Director then remains, the other directors shall designate two
persons to fill such vacancies who shall not be stockholders, affiliates or
associates of Purchaser or Parent and such persons shall be deemed to be
Independent Directors for purposes of this Agreement. Notwithstanding anything
in this Agreement to the contrary, in the event that Purchaser's designees are
elected to the Company's Board, after the acceptance for payment of Shares
pursuant to the Offer and prior to the Effective Time, the affirmative vote of a
majority of the Independent Directors shall be required to (i) amend or
terminate this Agreement by the Company, (ii) exercise or waive any of the
Company's rights, benefits or remedies hereunder or (iii) take any other action
by the Company's Board under or in connection with this Agreement.


                                       4
<PAGE>

                                   ARTICLE II

                                   THE MERGER

      SECTION 2.1 The Merger. Upon the terms and subject to the satisfaction or
waiver of the conditions hereof, and in accordance with the applicable
provisions of this Agreement and the General Corporation Law of the State of
Delaware (the "GCL"), at the Effective Time Purchaser shall be merged (the
"Merger") with and into the Company. Following the Merger, the separate
corporate existence of Purchaser shall cease and the Company shall continue as
the surviving corporation (the "Surviving Corporation"). At the option of Parent
and provided that such amendment does not delay the Effective Time, the Merger
may be structured so that, and this Agreement shall thereupon be amended to
provide that, the Company shall be merged with and into Purchaser or another
direct or indirect wholly-owned subsidiary of Parent with Purchaser or such
other subsidiary of Parent continuing as the Surviving Corporation; provided,
however, that the Company shall be deemed not to have breached any of its
representations and warranties herein if and to the extent such breach would
have been attributable to such election.

      SECTION 2.2 Effective Time; Closing. As soon as practicable after the
satisfaction or waiver (to the extent permitted hereunder) of the conditions set
forth in Article VII, the Company shall execute in the manner required by the
GCL and deliver to the Secretary of State of the State of Delaware a duly
executed and verified certificate of merger, or, if permitted, a certificate of
ownership and merger, and the parties shall take such other and further actions
as may be required by law to make the Merger effective. The time the Merger
becomes effective in accordance with applicable law is referred to as the
"Effective Time." Prior to such filing, a closing (the "Closing") shall be held
at the offices of Bressler, Amery & Ross, 17 State Street, 34th Floor, New York,
New York 10004, or such other place as the parties hereto shall agree, for the
purpose of confirming the satisfaction or waiver of the conditions set forth in
Article VII. The date on which the Closing occurs is referred to herein as the
"Closing Date."

      SECTION 2.3 Effects of the Merger; Subsequent Actions. The Merger shall
have the effects set forth in Section 259 of the GCL. Without limiting the
generality of the foregoing, and subject thereto and any other applicable laws,
at the Effective Time, all properties, rights, privileges, powers and franchises
of the Company and Purchaser shall vest in the Surviving Corporation, and all
debts, liabilities, restrictions, disabilities and duties of the Company and
Purchaser shall become debts, liabilities, restrictions, disabilities and duties
of the Surviving Corporation.

      SECTION 2.4 Certificate of Incorporation and By-Laws of the Surviving
Corporation.

      (a) The Certificate of Incorporation of the Company, as in effect
immediately prior to the Effective Time, shall be the Certificate of
Incorporation of the Surviving Corporation, until thereafter amended in
accordance with the provisions thereof and hereof and applicable law.

      (b) The By-Laws of Purchaser in effect at the Effective Time shall be the
By-Laws of the Surviving Corporation, until thereafter amended in accordance
with the provisions thereof and hereof and applicable law.


                                       5
<PAGE>

      SECTION 2.5 Directors. Subject to applicable law, the directors of
Purchaser immediately prior to the Effective Time shall be the initial directors
of the Surviving Corporation and shall hold office until their respective
successors are duly elected and qualified, or their earlier death, resignation
or removal.

      SECTION 2.6 Officers. The officers of the Purchaser immediately prior to
the Effective Time shall be the initial officers of the Surviving Corporation
and shall hold office until their respective successors are duly elected and
qualified, or their earlier death, resignation or removal.

      SECTION 2.7 Conversion of Shares. Subject to Section 3.1 below, at the
Effective Time, by virtue of the Merger and without any action on the part of
Parent, Purchaser, the Company or the holders of the following securities, each
Share issued and outstanding immediately prior to the Effective Time (other than
any Shares held by Parent, Purchaser, any wholly-owned subsidiary of Parent or
Purchaser, or in the treasury of the Company, which Shares, by virtue of the
Merger and without any action on the part of the holder thereof, shall be
cancelled and retired and shall cease to exist with no payment being made with
respect thereto, and other than Dissenting Shares) shall be converted into the
right to receive the Purchase Price, without interest thereon, upon surrender of
the certificate formerly representing such Share.

      SECTION 2.8 Conversion of Purchaser Common Stock. At the Effective Time,
each share of common stock, par value $.01 per share, of Purchaser issued and
outstanding immediately prior to the Effective Time shall, by virtue of the
Merger and without any action on the part of the holder thereof, be converted
into and become one validly issued, fully paid and non-assessable share of
common stock, par value $.10 per share, of the Surviving Corporation.

      SECTION 2.9 Stockholders' Meeting.

      (a) If required by the GCL in order to consummate the Merger, the Company,
acting through the Board, shall, in accordance with the GCL:

            (i) duly call, give notice of, convene and hold a special meeting of
its stockholders (the "Stockholders' Meeting") as soon as practicable following
the acceptance for payment of and payment for the Shares by Parent and/or
Purchaser pursuant to the Offer for the purpose of considering and taking action
upon this Agreement;

            (ii) prepare and file with the SEC a preliminary proxy or
information statement relating to the Merger and this Agreement and use its
reasonable best efforts (x) to obtain and furnish the information required to be
included by the SEC in the Proxy Statement (as hereinafter defined) and, after
consultation with Parent, to respond promptly to any comments made by the SEC
with respect to the preliminary proxy or information statement and cause a
definitive proxy or information statement (including any amendment or supplement
thereto, the "Proxy Statement") to be mailed to its stockholders, provided that
no amendment or supplement to the Proxy Statement will be made by the Company
without consultation with Parent and its counsel and (y) to obtain the necessary
approvals of the Merger and this Agreement by its stockholders; and

            (iii) subject to the fiduciary obligations of the Board under
applicable law, include in the


                                       6
<PAGE>

Proxy Statement the recommendation of the Board that stockholders of the Company
vote in favor of the approval of the Merger and the adoption of this Agreement.

      (b) At such meeting, each of Parent and Purchaser will vote (and will
cause each of their respective affiliates to vote), all of the Shares (if any)
then owned by them (or their respective affiliates) in favor of the approval of
the Merger and the adoption of this Agreement.

      SECTION 2.10 Merger Without Meeting of Stockholders. Notwithstanding
Section 2.9, in the event that Parent, Purchaser or any other subsidiary of
Parent shall acquire at least 90% of the Shares pursuant to the Offer and the
Stock Tender Agreement, the parties hereto agree to take all necessary and
appropriate action to cause the Merger to become effective as soon as
practicable after the acceptance for payment of and payment for Shares by Parent
and/or Purchaser pursuant to the Offer without a meeting of stockholders of the
Company, in accordance with Section 253 of the GCL.

                                   ARTICLE III

                      DISSENTING SHARES; PAYMENT FOR SHARES

      SECTION 3.1 Dissenting Shares. Notwithstanding anything in this Agreement
to the contrary, Shares outstanding immediately prior to the Effective Time and
held by a holder who has not voted in favor of the Merger or consented thereto
in writing and who has demanded appraisal for such Shares in accordance with
Section 262 of the GCL, if such Section 262 provides for appraisal rights for
such Shares in the Merger ("Dissenting Shares"), shall not be converted into the
right to receive the Purchase Price as provided in Section 2.7, unless and until
such holder fails to perfect or withdraws or otherwise loses his right to
appraisal and payment under the GCL. If, after the Effective Time, any such
holder fails to perfect or withdraws or loses his right to appraisal, such
Dissenting Shares shall thereupon be treated as if they had been converted as of
the Effective Time into the right to receive the Purchase Price, if any, to
which such holder is entitled, without interest or dividends thereon. The
Company shall give Parent prompt notice of any demands received by the Company
for appraisal of Shares and, prior to the Effective Time, Parent shall have the
right to participate in all negotiations and proceedings with respect to such
demands. Prior to the Effective Time, the Company shall not, except with the
prior written consent of Parent, make any payment with respect to, or settle or
offer to settle, any such demands.

      SECTION 3.2 Exchange of Certificates.

      (a) Prior to the Effective Time, Parent shall designate a bank or trust
company reasonably acceptable to the Company to act as paying agent (the "Paying
Agent") in effecting the exchange for the Purchase Price of certificates (the
"Certificates") that, prior to the Effective Time, represented Shares. Upon the
surrender of each such Certificate formerly representing Shares, together with a
properly completed letter of transmittal, the Paying Agent shall pay the holder
of such Certificate the Purchase Price multiplied by the number of Shares
formerly represented by each such Certificate, in exchange therefor, and each
such Certificate shall forthwith be cancelled. Until so surrendered and
exchanged, each such Certificate (other than Certificates representing
Dissenting Shares or Shares held by Parent, Purchaser or the Company, or any
direct or indirect subsidiary thereof, or in the treasury of the Company) shall
represent solely the right to receive the Purchase Price. No interest shall be
paid or accrue on the Purchase Price. If the Purchase Price (or any portion
thereof) is to be delivered to any


                                       7
<PAGE>

person other than the person in whose name the Certificate formerly representing
Shares surrendered in exchange therefor is registered, it shall be a condition
to such exchange that the Certificate so surrendered shall be properly endorsed
or otherwise be in proper form for transfer and that the person requesting such
exchange shall pay to the Paying Agent any transfer or other Taxes required by
reason of the payment of the Purchase Price to a person other than the
registered holder of the Certificate surrendered, or shall establish to the
satisfaction of the Paying Agent that such Tax has been paid or is not
applicable.

      (b) Prior to the Effective Time, Parent or Purchaser shall deposit, or
cause to be deposited, in trust with the Paying Agent such funds as needed for
timely payment hereunder; provided, however, that no such deposit shall relieve
Parent or Purchaser of their obligation to pay the Purchase Price pursuant to
Section 2.7.

      (c) The Purchase Price shall be invested by the Paying Agent as directed
by Parent, provided that such investments shall be limited to direct obligations
of the United States of America, obligations for which the full faith and credit
of the United States of America is pledged to provide for the payment of
principal and interest, commercial paper rated of the highest quality by Moody's
Investors Services, Inc. or Standard & Poor's Corporation, or certificates of
deposit issued by a commercial bank having at least $1,000,000,000 in assets;
provided further that no loss on investment made pursuant to this Section 3.2(c)
shall relieve Parent or Purchaser of their obligation to pay the Purchase Price
pursuant to Section 2.7.

      (d) Promptly after the Effective Time, the Paying Agent shall mail to each
record holder of Certificates that immediately prior to the Effective Time
represented Shares a form of letter of transmittal and instructions for use in
surrendering such Certificates and receiving the Purchase Price in exchange
therefor.

      (e) After the Effective Time, there shall be no transfers on the stock
transfer books of the Surviving Corporation of any Shares. If, after the
Effective Time, Certificates formerly representing Shares are presented to the
Surviving Corporation or the Paying Agent, they shall be cancelled and exchanged
for the Purchase Price as provided in this Article III, subject to applicable
law in the case of Dissenting Shares.

      (f) Promptly following the date which is six months after the Effective
Time, the Paying Agent shall deliver to Parent all cash and documents in its
possession relating to the transactions described in this Agreement, and the
Paying Agent's duties shall terminate. Thereafter, each holder of a Certificate
formerly representing a Share may surrender such Certificate to the Surviving
Corporation and (subject to applicable abandoned property, escheat and similar
laws) receive in exchange therefor the Purchase Price, without any interest
thereon.


                                       8
<PAGE>

                                   ARTICLE IV

                  REPRESENTATIONS AND WARRANTIES OF THE COMPANY

      The Company represents and warrants to Parent and Purchaser that:

      SECTION 4.1 Organization and Qualification; Subsidiaries. The Company is a
corporation duly organized, validly existing and in good standing under the laws
of the State of Delaware. Each entity which the Company owns, directly or
indirectly, a majority of the outstanding voting securities (each a "Subsidiary"
or collectively the "Subsidiaries") is a corporation duly organized, validly
existing and in good standing under the laws of the jurisdiction of its
incorporation. Each of the Company and its Subsidiaries has the requisite
corporate power and authority to own, operate or lease its properties and to
carry on its business as it is now being conducted, and is duly qualified or
licensed to do business, and is in good standing, in each jurisdiction in which
the nature of its business or the properties owned, operated or leased by it
makes such qualification, licensing or good standing necessary, except where the
failure to have such power or authority, or the failure to be so qualified,
licensed or in good standing, would not have a Material Adverse Effect on the
Company. The term "Material Adverse Effect on the Company," as used in this
Agreement, means any adverse change, circumstance or effect that, individually
or in the aggregate with all other adverse changes, circumstances and effects,
has had or will have a material adverse effect on the business, financial
condition, properties or results of operations of the Company and its
Subsidiaries taken as a whole, other than any adverse change, circumstance or
effect relating to or arising out of (i) the economy or securities markets in
general, (ii) the announcement of the Agreement or the transactions contemplated
hereby (including any impact on employees, vendors or customers resulting
therefrom) or (iii) the industry of the Company and its Subsidiaries in general,
and not specifically relating to the Company or its Subsidiaries.

      SECTION 4.2 Charter and By-laws. The Company has heretofore made available
to Parent a complete and correct copy of the charter and the By-laws or
comparable organizational documents, each as amended as of the date hereof, of
the Company and each of its Subsidiaries.

      SECTION 4.3 Capitalization.

      (a) The authorized capital stock of the Company consists of 12,000,000
shares of Common Stock, $.10 par value per share ("Common Stock") and 1,000,000
shares of preferred stock, par value $1.00 per share ("Preferred Stock"). As of
the close of business on May 15, 1998, 3,510,251 shares of Common Stock were
issued and outstanding, excluding 2,336,990 shares of Common Stock in treasury.
As of the date hereof there were no shares of Preferred Stock issued and
outstanding. The Company has no shares of capital stock reserved for future
issuance. The Company has no outstanding options to purchase any shares of
capital stock. Since March 31, 1998 the Company has not issued any shares of
capital stock. There are no bonds, debentures, notes or other indebtedness
having general voting rights (or convertible into securities having such rights)
("Voting Debt") of the Company or any of its Subsidiaries issued and
outstanding. There are no existing options, warrants, calls, subscriptions or
other rights, convertible securities, agreements, arrangements or commitments of
any character, relating to the issued or unissued capital stock of the Company
or any of its Subsidiaries, obligating the Company or any of its Subsidiaries to
issue, transfer or sell or cause to be issued, transferred or sold any shares of
capital stock or Voting Debt of, or other equity interest in, the Company or any
of its Subsidiaries or securities 


                                       9
<PAGE>

convertible into or exchangeable for such shares or equity interests, and
neither the Company nor any of its Subsidiaries is obligated to grant, extend or
enter into any such option, warrant, call, subscription or other right,
convertible security, agreement, arrangement or commitment. There are no
outstanding contractual obligations of the Company or any of its Subsidiaries to
(i) repurchase, redeem or otherwise acquire any shares of capital stock of the
Company or any of its Subsidiaries or (ii) provide funds to or make any
investment in (in the form of a loan, capital contribution or otherwise) any
entity other than a wholly-owned Subsidiary.

      (b) Each of the outstanding shares of capital stock of each of the Company
and its Subsidiaries is duly authorized, validly issued, fully paid and
nonassessable, and such shares of capital stock of the Subsidiaries as are owned
by the Company or by a Subsidiary of the Company are owned in each case free and
clear of any lien, claim, option, charge, security interest, limitation,
encumbrance and restriction of any kind (any of the foregoing being a "Lien").
All outstanding shares of capital stock of each of the Subsidiaries are owned by
the Company.

      (c) There are no voting trusts or other agreements or understandings to
which the Company or any of its Subsidiaries is a party with respect to the
voting of the capital stock of the Company or any of its Subsidiaries.

      SECTION 4.4 Authority Relative to this Agreement.

      The Company has all necessary corporate power and authority to execute and
deliver this Agreement, and to consummate the transactions contemplated hereby
and thereby. The execution and delivery of this Agreement by the Company and the
consummation by the Company of the transactions contemplated hereby have been
duly and validly authorized and approved by the Board and no other corporate
proceedings on the part of the Company are necessary to authorize or approve
this Agreement, or to consummate the transactions contemplated hereby (other
than, with respect to the Merger, and subject to Section 2.10, the approval and
adoption of the Merger and this Agreement by the affirmative vote of the holders
of a majority of the Shares then outstanding). This Agreement has been duly and
validly executed and delivered by the Company and, assuming the due and valid
authorization, execution and delivery of this Agreement by Parent and Purchaser,
constitutes a valid and binding obligation of the Company enforceable against
the Company in accordance with its terms, except that such enforceability (i)
may be limited by bankruptcy, insolvency, moratorium or other similar laws
affecting or relating to the enforcement of creditors' rights generally and (ii)
is subject to general principles of equity.

      SECTION 4.5 No Conflict; Required Filings and Consents.

      (a) None of the execution, delivery or performance of this Agreement by
the Company, the consummation by the Company of the transactions contemplated
hereby or the compliance by the Company with any of the provisions hereof will
(i) conflict with or violate the Certificate of Incorporation or By-Laws of the
Company or the comparable organizational documents of any of its Subsidiaries,
(ii) conflict with or violate any statute, ordinance, rule, regulation, order,
judgment or decree applicable to the Company or its Subsidiaries, or by which
any of them or any of their respective properties or assets may be bound or
affected, or (iii) result in a violation or breach of or constitute a default
(or an event which with notice or lapse of time or both would become a default)
under, or give to others any rights of termination, amendment, acceleration or
cancellation of, or result in any loss of any material benefit, or 


                                       10
<PAGE>

the creation of any Lien on any of the property or assets of the Company or any
of its Subsidiaries (any of the foregoing referred to in clause (ii) or this
clause (iii) being a "Violation") pursuant to, any note, bond, mortgage,
indenture, contract, agreement, lease, license, permit, franchise or other
instrument or obligation to which the Company or any of its Subsidiaries is a
party or by which the Company or any of its Subsidiaries or any of their
respective properties may be bound or affected, except in the case of the
foregoing clauses (ii) or (iii) for any such Violations which would not in the
aggregate have a Material Adverse Effect on the Company or limit or restrict the
ability of the Company to consummate the transactions contemplated hereby or
thereby.

      (b) None of the execution, delivery or performance of this Agreement by
the Company, the consummation by the Company of the transactions contemplated
hereby or the compliance by the Company with any of the provisions hereof will
require any consent, waiver, approval, authorization or permit of, or
registration or filing with or notification to (any of the foregoing being a
"Consent"), any government or subdivision thereof, domestic, foreign or
supranational or any administrative, governmental or regulatory authority,
agency, commission, tribunal or body, domestic, foreign or supranational (a
"Governmental Entity"), except for (i) compliance with any applicable
requirements of the Securities Exchange Act of 1934, as amended (the "Exchange
Act"), (ii) the filing of a certificate of merger, or, if permitted, a
certificate of ownership and merger, pursuant to the GCL, (iii) notifications
required by certain state Blue Sky, takeover and environmental statutes, (iv)
compliance with the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as
amended (the "HSR Act") and any requirements of any foreign or supranational
Antitrust Laws, and (v) Consents, the failure of which to obtain or make would
not in the aggregate have a Material Adverse Effect on the Company or limit or
restrict the ability of the Company to consummate the transactions contemplated
hereby.

      SECTION 4.6 SEC Reports and Financial Statements.

      (a) The Company has filed with the SEC all forms, reports, schedules,
registration statements and definitive proxy statements required to be filed by
the Company with the SEC since January 1, 1997 (the "SEC Reports"). As of their
respective dates, the SEC Reports (including, without limitation, any financial
statements or schedules included therein) complied in all material respects with
the requirements of the Exchange Act or the Securities Act of 1933, as amended,
and the rules and regulations of the SEC promulgated thereunder applicable, as
the case may be, to such SEC Reports, and none of the SEC Reports contained any
untrue statement of a material fact or omitted to state a material fact required
to be stated therein or necessary to make the statements made therein, in light
of the circumstances under which they were made, not misleading.

      (b) The audited consolidated financial statements and unaudited
consolidated interim financial statements of the Company included in the SEC
Reports and the audited financial statements as of and for the year ended
December 31, 1997, which the Company has provided to Parent, present fairly in
all material respects the consolidated financial position and the consolidated
results of operations and cash flows of the Company and its consolidated
Subsidiaries as of the dates or for the periods presented therein in conformity
with United States generally accepted accounting principles ("GAAP") applied on
a consistent basis during the periods involved except as otherwise noted
therein, including the related notes. The Company has also provided to Parent
unaudited condensed consolidated financial statements for the period ending
March 31, 1998, filed with the SEC on May 15, 1998. Such statements were
prepared in accordance with generally accepted accounting principles for interim
financial information and with the


                                       11
<PAGE>

instructions to SEC Form 10-Q and Article 10 of Regulation S-X promulgated under
the Exchange Act and, in the opinion of management, all adjustments consisting
of normal recurring accruals considered necessary for a fair presentation have
been included.

      SECTION 4.7 Information. None of the information provided or that may be
provided by the Company for use in the Offer Documents, the Schedule 14D-1 or
any other document to be filed with the SEC or any other Governmental Entity in
connection with the transactions contemplated by this Agreement (the "Other
Filings"), and neither the Proxy Statement nor the Schedule 14D-9, shall, at the
time filed with the SEC or such other Governmental Entity, and, in the case of
the Proxy Statement, at the time mailed to the Company's stockholders, at the
time of the Stockholders' Meeting or at the Effective Time, contain any untrue
statement of a material fact or omit to state any material fact required to be
stated therein or necessary in order to make the statements therein, in light of
the circumstances under which they are made, not misleading. Notwithstanding the
foregoing, the Company makes no representation or warranty with respect to any
information provided or that may be provided by Parent or Purchaser specifically
for use in such documents. The Schedule 14D-9 and the Proxy Statement will
comply as to form in all material respects with the provisions of the Exchange
Act and the rules and regulations thereunder.

      SECTION 4.8 Changes. Since December 31, 1997, except as set forth in the
SEC Reports filed prior to the date hereof or as otherwise disclosed in Schedule
4.8 hereto:

      (a) there has been no event, effect or change (including the incurrence of
any liabilities or obligations of any nature whether or not accrued, contingent
or otherwise) having a Material Adverse Effect on the Company;

      (b) the Company has not adopted any amendment to its Certificate of
Incorporation or By-laws;

      (c) the Company has not issued, reissued, pledged or sold, or authorized
the issuance, reissuance, pledge or sale of (i) additional shares of capital
stock of any class, or securities convertible into, exchangeable for or
evidencing the right to substitute for, capital stock of any class, or any
rights, warrants, options, calls, commitments or any other agreements of any
character, to purchase or acquire any capital stock or any securities or rights
convertible into, exchangeable for, or evidencing the right to subscribe for,
capital stock, or (ii) any other securities in respect of, in lieu of, or in
substitution for, Shares;

      (d) neither the Company nor any of its Subsidiaries declared, set aside or
paid any dividend or other distribution (whether in cash, securities or property
or any combination thereof) in respect of any class or series of its capital
stock other than between the Company and any of its wholly-owned Subsidiaries,
or its regular quarterly dividend of $.32 per share of Common Stock to
stockholders of record on March 23, 1998;

      (e) Neither the Company nor any of its Subsidiaries has split, combined,
subdivided, reclassified or redeemed, purchased or otherwise acquired or
proposed to redeem or purchased or otherwise acquired any shares of its capital
stock or any of its other securities; and


                                       12
<PAGE>

      (f) Neither the Company nor any of its Subsidiaries has taken or omitted
to take any action, nor has any event occurred, which (if taken, omitted or
occurring after the date hereof) would constitute a breach of Section 6.1 of
this Agreement.

      SECTION 4.9 Opinion of Financial Advisor. The Company has received the
opinion of Salomon Brothers Inc and Smith Barney Inc. collectively doing
Business as "Salomon Smith Barney" ("Salomon Smith Barney"), dated the date
hereof, to the effect that, as of such date, the Purchase Price is fair to the
holders of Shares, a copy of which opinion has been delivered to Parent. The
Company has been authorized by Salomon Smith Barney to permit inclusion of such
opinion (and reference thereto) in the Offer Documents, the Schedule 14D-9 and
the Proxy Statement.

      SECTION 4.10 Takeover Statutes. The Company is subject to Section 203 of
the GCL. By reason of action taken by the Company, such section is not
applicable to the transactions contemplated hereby.

      SECTION 4.11 Litigation. Except as set forth in Schedule 4.11 there are no
suits, claims, actions, proceedings, including, without limitation, arbitration
proceedings or alternative dispute resolution proceedings, or investigations
pending or, to the knowledge of the Company, threatened against the Company or
any of its Subsidiaries not set forth in the SEC Reports filed prior to the date
hereof.

      SECTION 4.12 Employee Plans and Arrangements.

      (a) Schedule 4.12(a) lists each "employee pension benefit plan" (as
defined in Section 3(2) of the Employee Retirement Income Security Act of 1974,
as amended ("ERISA")) (hereinafter a "Pension Plan") and "employee welfare
benefit plan" (as defined in Section 3 (i) of ERISA, (hereinafter a "Welfare
Plan") and each pension, retirement, bonus, incentive compensation, profit
sharing, stock option, stock purchase, stock bonus, phantom stock, deferred
compensation, hospitalization, medical, dental, vision, life insurance,
accidental death and dismemberment insurance, business travel insurance,
cafeteria and flexible spending, sick pay, disability, severance, golden
parachute, or other plans, policy, contract, fund or arrangement maintained or
contributed to, or required to be maintained or contributed to, by the Company,
any of its Subsidiaries or any other person that, together with the Company, is
treated as a single employer under Section 4.14(b), (c), (m) or (o) of the
Internal Revenue Code of 1986, as amended (the "Code") (each a "Commonly
Controlled Entity") for the benefit of any present or former employees of the
Company or any of its Subsidiaries. The Company has never maintained, or
incurred any liability whatsoever, with respect to a multiemployer plan (as
defined in Section 4001(a)(3) of ERISA). The Company has made available to
Purchaser true, complete and correct copies of (i) each Pension Plan and Welfare
Plan collectively, the ("Benefit Plans") (ii) the most recent annual report on
Form 5500 as filed with the Internal Revenue Service with respect to, (iii) the
most recent summary plan description (or similar document) with respect to each
applicable Benefit Plan, and (iv) each trust agreement relating to the Pension
Plan.

      (b) Except where a failure would not have a Material Adverse Effect on the
Company, each Benefit Plan has been administered in accordance with its terms.
Except where a failure would not have a Material Adverse Effect on the Company,
the Company, its Subsidiaries all the Benefit Plans are in compliance with the
applicable provisions of ERISA, the Code, and all other laws, ordinances or
regulations of any Governmental Entities. Except where a failure would not have
a Material Adverse 


                                       13
<PAGE>

Effect on the Company, there are no investigations by any Governmental Entities,
termination proceedings or other claims (except claims for benefits payable in
the normal operations of the Pension Plans), suits or proceedings against or
involving any Benefit Plan or asserting any rights to or claims for benefits
under any Benefit Plan.

      (c) Except where a failure would not have a Material Adverse Effect on the
Company, (i) all contributions to the Benefit Plan required to be made by the
Company or any of its Subsidiaries in accordance with the terms of the Benefit
Plans, and, when applicable, Section 302 of ERISA or Section 412 of the Code,
have been timely made, (ii) there has been no application for or waiver of the
minimum funding standards imposed by Section 412 of the Code with respect to any
Benefit Plan that is a Pension Plan and (iii) no Pension Plan had an
"accumulated funding deficiency" within the meaning of Section 412(a) of the
Code as of the end of the most recently completed plan year.

      (d) (i) Each Pension Plan that is intended to be a tax-qualified plan has
been the subject of a post Tax Reform Act of 1986 determination letter from the
Internal Revenue Service to the effect that such Company Pension Plan and each
related trust is qualified and exempt from Federal income taxes under Sections
401(a) and 501(a), respectively, of the Code; (ii) No such determination letter
has been revoked, and revocation has not been threatened; (iii) No event has
occurred and no circumstances exist that would adversely affect the
tax-qualification of such Pension Plan except for any events or circumstances
that would not have a Material Adverse Effect on the Company; and (iv) Such
Pension Plan has not been amended since the effective date of its most recent
determination letter in any respect that might adversely affect its
qualification, increase its cost or require security under Section 307 of ERISA.
The Company has made available to Purchaser a copy of the most recent
determination letter received with respect to each Pension Plan for which such a
letter has been issued, as well as a copy of any pending application for a
determination letter.

      (e) Except where a failure would not have a Material Adverse Effect on the
Company: (i) no non-exempt "prohibited transaction" (as defined in Section 4975
of the Code or Section 406 of ERISA) has occurred that involves the assets of
any Benefit Plan; (ii) no Pension Plan has been terminated or has been the
subject of a "reportable event" (as defined in Section 4043 of ERISA and the
regulations thereunder) for which the 30-day notice requirement has not been
waived by the Pension Benefit Guaranty Corporation ("PBGC"); and (iii) none of
the Company, any of its Subsidiaries or any trustee, administrator or other
fiduciary of the Pension Plan has engaged in any transaction or acted in a
manner that could, or has failed to act so as to, subject the Company, any such
Subsidiary or any trustee, administrator or other fiduciary to any liability for
breach of fiduciary duty under ERISA or any other applicable law.

      (f) No Commonly Controlled Entity has incurred any liability to a Pension
Plan (other than for contributions not yet due) or to the PBGC (other than for
the payment of premiums not yet due other than liabilities that would have a
Material Adverse Effect on the Company).

      (g) Except where the failure would not have a Material Adverse Effect on
the Company, no Commonly Controlled Entity has (i) engaged in a transaction
described in Section 4069 of ERISA that could subject the Company to a liability
at any time after the date hereof or (ii) acted in a manner that could, or
failed to act so as to, result in fines, penalties, taxes or related charges
under (x) Section 502(c), (i) or (1) of ERISA, (y) Section 4071 of ERISA or (z)
Chapter 43 of the Code.


                                       14
<PAGE>

      (h) The Company and its Subsidiaries comply with the applicable
requirements of parts 6 and 7 of subtitle B of Title I of ERISA ((S)(S) 601 et
seq.) with respect to each Benefit Plan that is a group health plan, as such
term is defined in Section 5000(b)(1) of the Code and other than medical
continuation requirements mandated pursuant to (S)(S) 601 et seq. no Benefit
Plan that is a group health plan provides or is required to provide post
employment or post retirement medical or health benefits to any former employees
or employees of the Company or any Commonly Controlled Entity.

      (i) Schedule 4.12(i) lists (i) all employment agreements between the
Company or any of its Subsidiaries and any of their respective directors or
officers and between the Company or any of its Subsidiaries and any of its or
their employees which is not terminable by the Company or its Subsidiaries on
less than 90 days' notice, and (ii) all agreements and plans pursuant to which
any director, officer or employee of the Company or any of its subsidiaries is
entitled to benefits upon termination of their employment or a change in control
of the Company.

      (j) Except as set forth in Schedule 4.12(j), none of the employees of the
Company or any of its Subsidiaries is represented by a union or subject to a
collective bargaining agreement.

      SECTION 4.13 Assets. The Company or one of its Subsidiaries has (a) good
and marketable title to or a valid leasehold interest under a capitalized lease
in all assets recorded on the Company's balance sheet as of December 31, 1997
included in the financial statements referred to in Section 4.6(b), except for
assets disposed of in the ordinary course of business since such date, and (b) a
valid leasehold or other interest in all other assets used by it in its
business, except in each case for exceptions to the foregoing that would not
have a Material Adverse Effect on the Company. The consummation of the
transactions contemplated hereby will not affect the ownership or right to use
any of the Company's assets, except for exceptions to the foregoing that would
not have a Material Adverse Effect on the Company.

      SECTION 4.14 Intellectual Property.

      (a) Except for any exceptions to the following that would not have a
Material Adverse Effect on the Company, the Company and its Subsidiaries own or
have the right to use the Intellectual Property used by it and reasonably
necessary for the Company and its Subsidiaries to conduct their business as it
is currently conducted or proposed to be conducted and consistent with past
practice.

      (b) Except for any exceptions to the following that would not have a
Material Adverse Effect on the Company: (i) all of the registered Intellectual
Property owned by the Company and its Subsidiaries is subsisting and unexpired
(except as such has expired by the passing of time without the possibility of
extension or renewal), free of all Liens, has not been abandoned and, to the
knowledge of the Company, all Intellectual Property used by the Company whether
or not registered does not infringe the Intellectual Property rights of any
third party; (ii) none of the Intellectual Property owned by the Company and its
Subsidiaries is the subject of any license, security interest or other agreement
granting rights therein to any third party, except as set forth on Schedule
4.14(b), (iii) to the knowledge of the Company, no judgment, decree, injunction,
rule or order has been rendered by any Governmental Entity which would limit,
cancel or question the validity of, or the Company's or its Subsidiaries' rights
in and to, any Intellectual Property owned by the Company; and (iv) the Company
has not received notice of any pending or threatened suit,


                                       15
<PAGE>

action or proceeding that seeks to limit, cancel or question the validity of, or
the Company's or its Subsidiaries' rights in and to, any Intellectual Property.

      (c) For purposes of this Agreement "Intellectual Property" shall mean all
rights, privileges and priorities provided under U.S., state and foreign law
relating to intellectual property, including without limitation all (i)(A)
inventions, discoveries, processes, formulae, designs, methods, techniques,
procedures, concepts, developments, technology, new and useful improvements
thereof and know-how relating thereto, whether or not patented or eligible for
patent protections; (B) copyrights and copyrightable works, including computer
applications, programs, software, databases and related items; (C) trademarks,
service marks, trade names, and trade dress, the goodwill of any business
symbolized thereby, and all common-law rights relating thereto; and (D) trade
secrets and other confidential information; and (ii) all registrations,
applications, recordings, and licenses or other similar agreements related to
the foregoing.

      SECTION 4.15 Taxes. The Company and each of its Subsidiaries have (i)
filed all Tax Returns which they are required to file under applicable laws and
regulations, (ii) paid all Taxes which have become due and payable, and (iii)
accrued as a liability on the balance sheet included in the Company's 1997
financial statements described in Section 4.6 all Taxes which were accrued but
not yet due and payable as of the date thereof, except for failures to take any
of such actions which, individually or in the aggregate, would not have a
Material Adverse Effect on the Company. For purposes of this Agreement, "Tax" or
"Taxes" shall mean any federal, state, local or foreign income, gross receipts,
franchise, estimated, alternative minimum, add-on minimum, sales, use, transfer,
registration, value added, excise, natural resources, severance, stamp,
occupation, premium, windfall profit, environmental, customs, duties, real
property, personal property, capital stock, social security, unemployment,
disability, payroll, license, employee or other withholding, or other tax of any
kind, including any interest or penalties in respect of the foregoing, and "Tax
Returns" means returns, declarations, reports, information returns, or other
documents filed or required to be filed in connection with the determination,
assessment or collection of Taxes of any person or the administration of any
laws, regulations or administrative requirements relating to any Taxes.

      SECTION 4.16 Environmental Laws and Regulations. Except as disclosed in
Schedule 4.16:

            (i) The Company and its Subsidiaries hold and are in compliance with
all Environmental Permits (as defined below), and the Company and its
Subsidiaries are otherwise in compliance with all Environmental Laws (as defined
below) and there are no conditions that might prevent or interfere with such
compliance in the future, except where the failure to hold or to be in such
compliance would not reasonably be expected to have a Material Adverse Effect on
the Company;

            (ii) As of the date hereof, neither the Company nor any of its
Subsidiaries has received any Environmental Claim (as defined below) and there
is no threatened Environmental Claim that would reasonably be expected to have a
Material Adverse Effect on the Company;

            (iii) Neither the Company nor any of its Subsidiaries has entered
into any consent decree, order or agreement under any Environmental Law;

            (iv) There are no (A) underground storage tanks, (B) polychlorinated
biphenyls, 


                                       16
<PAGE>

(C) friable asbestos or asbestos-containing materials, (D) sumps, (E) surface
impoundments, (F) landfills, or (G) sewers or septic systems present at any
facility currently owned by the Company or any of its Subsidiaries the presence
of which would reasonably be expected to have a Material Adverse Effect on the
Company;

            (v) None of the Company or its Subsidiaries has contractually
assumed any liabilities or obligations under any Environmental Laws that would
reasonably be expected to have a Material Adverse Effect on the Company;

            (vi) To the knowledge of the Company, there has not been any Release
of Hazardous Materials at any property currently or formerly owned or operated
by the Company, any of its Subsidiaries or predecessors in interest nor, to the
knowledge of the Company, at any disposal facility that may have received
Hazardous Materials generated by the Company, any of its Subsidiaries or a
predecessor in interest; and

            (vii) For purposes of this Agreement, the following terms shall have
the following meanings: (A) "Environmental Claim" means any written or oral
notice, claim, demand, action, suit, complaint, proceeding or other
communication by any person alleging liability or potential liability (including
without limitation liability or potential liability for investigatory costs,
cleanup costs, governmental response costs, natural resource damages, property
damage, personal injury, reasonable engineering and attorneys fees, fines or
penalties) arising out of, relating to, based on or resulting from (1) the
presence, discharge, emission, release or threatened release of any Hazardous
Materials at any location, whether or not owned, leased or operated by the
Company or any of its Subsidiaries or (2) circumstances forming the basis of any
violation or alleged violation of any Environmental Law or Environmental Permit
or (3) otherwise relating to obligations or liabilities under any Environmental
Laws; (B) "Environmental Permits" means all permits, licenses, registrations and
other governmental authorizations required under Environmental Laws for the
Company and its Subsidiaries to conduct their operations and businesses on the
date hereof and consistent with past practices; (C) "Environmental Laws" means
all applicable federal, state and local statutes, rules, regulations,
ordinances, orders, decrees and common law relating in any manner to
contamination, pollution or protection of the environment, including without
limitation the Comprehensive Environmental Response, Compensation and Liability
Act, the Solid Waste Disposal Act, the Clean Air Act, the Clean Water Act, the
Toxic Substances Control Act, the Occupational Safety and Health Act, the
Emergency Planning and Community-Right-to-Know Act, the Safe Drinking Water Act,
all as amended, and similar state laws; (D) "Hazardous Materials" means all
hazardous or toxic substances, wastes, materials or chemicals, petroleum
(including crude oil or any fraction thereof) and petroleum products, solid
waste, special waste, friable asbestos and asbestos-containing materials,
pollutants, contaminants and all other materials, and substances regulated
pursuant to, or that could reasonably be expected to provide the basis of
liability under, any Environmental Law and (E) "Release" means any spilling,
leaking, pumping, emitting, emptying, discharging, injecting, escaping,
leaching, migrating, dumping, or disposing of Hazardous Materials (including the
abandonment or discarding of barrels, containers or other closed receptacles
containing Hazardous Materials) into the environment.

      SECTION 4.17 Insurance. Schedule 4.17 sets forth insurance policies in
force for the benefit of the Company as of April 15, 1998. All such policies
have been renewed in the ordinary course of business consistent with past
practice.


                                       17
<PAGE>

      SECTION 4.18 Brokers. Except for the engagement of Salomon Smith Barney,
whose fees will be paid by the Company and a copy of whose engagement letter has
been provided to Parent, none of the Company, any of its Subsidiaries, or any of
their respective officers, directors or employees has employed any broker or
finder or incurred any liability for any brokerage fees, commissions or finder's
fees in connection with the transactions contemplated by this Agreement.

                                    ARTICLE V

                         REPRESENTATIONS AND WARRANTIES
                             OF PARENT AND PURCHASER

      Parent and Purchaser represent and warrant to the Company that:

      SECTION 5.1 Organization and Qualification. Parent is a corporation duly
organized, validly existing and in good standing under the laws of Massachusetts
and each material subsidiary of Parent is a corporation duly organized, validly
existing and in good standing under the laws of the jurisdiction of its
organization. Purchaser is a corporation duly organized, validly existing and in
good standing under the laws of the State of Delaware. Each of Parent and its
material subsidiaries (including Purchaser) has the requisite corporate power
and authority to own, operate or lease its properties and to carry on its
business as it is now being conducted, and is duly qualified or licensed to do
business, and is in good standing, in each jurisdiction in which the nature of
its business or the properties owned, operated or leased by it makes such
qualification, licensing or good standing necessary, except where the failure to
have such power or authority, or the failure to be so qualified, licensed or in
good standing, would not have a Material Adverse Effect on Parent. The term
"Material Adverse Effect on Parent," as used in this Agreement, means any
adverse change, circumstance or effect that, individually or in the aggregate
with all other adverse changes, circumstances and effects, has had or will have
a materially adverse effect on the business, financial condition, properties or
results of operations of Parent and its Subsidiaries taken as a whole.

      SECTION 5.2 Authority Relative to this Agreement and the Stock Purchase
Agreements. Each of Parent and Purchaser has all necessary corporate power and
authority to execute and deliver this Agreement, and to consummate the
transactions contemplated hereby. The execution and delivery of this Agreement
by Parent and Purchaser and the consummation by Parent and Purchaser of the
transactions contemplated hereby have been duly and validly authorized and
approved by the Boards of Directors of Parent and Purchaser and by Parent as
stockholder of Purchaser, and no other corporate proceedings on the part of
Parent or Purchaser are necessary to authorize or approve this Agreement, or to
consummate the transactions contemplated hereby. This Agreement has been duly
executed and delivered by each of Parent and Purchaser and, assuming the due and
valid authorization, execution and delivery by the Company, constitutes a valid
and binding obligation of each of Parent and Purchaser enforceable against each
of them in accordance with its terms, except that such enforceability (i) may be
limited by bankruptcy, insolvency, moratorium or other similar laws affecting or
relating to the enforcement of creditors' rights generally and (ii) is subject
to general principles of equity.

      SECTION 5.3 No Conflict; Required Filings and Consents.


                                       18
<PAGE>

      (a) None of the execution, delivery or performance of this Agreement by
Parent or Purchaser, the consummation by Parent or Purchaser of the transactions
contemplated hereby or compliance by Parent or Purchaser with any of the
provisions hereof will (i) conflict with or violate the organizational documents
of Parent or Purchaser, (ii) conflict with or violate any statute, ordinance,
rule, regulation, order, judgment or decree applicable to Parent or Purchaser,
or any of their subsidiaries, or by which any of them or any of their respective
properties or assets may be bound or affected, or (iii) result in a violation
pursuant to any note, bond, mortgage, indenture, contract, agreement, lease,
license, permit, franchise or other instrument or obligation to which Parent or
Purchaser, or any of their subsidiaries, is a party or by which any of their
respective properties or assets may be bound or affected, except in the case of
the foregoing clauses (ii) and (iii) for any such violations which would not
have a Material Adverse Effect on Parent or limit or restrict the ability of
Parent or Purchaser to consummate the transactions contemplated hereby.

      (b) None of the execution and delivery of this Agreement by Parent and
Purchaser, the consummation by Parent and Purchaser of the transactions
contemplated hereby or compliance by Parent and Purchaser with any of the
provisions hereof will require any Consent of any Governmental Entity, except
for (i) compliance with any applicable requirements of the Exchange Act, (ii)
the filing of a certificate of merger, or, if permitted, a certificate of
ownership and merger, pursuant to the GCL, (iii) notifications required by
certain state Blue Sky, takeover and environmental statutes, (iv) compliance
with the HSR Act and any requirements of any foreign or supranational Antitrust
Laws and (v) Consents the failure of which to obtain or make would not have a
Material Adverse Effect on Parent or limit or restrict the ability of Parent or
Purchaser to consummate the transactions contemplated hereby.

      SECTION 5.4 Information. None of the information provided or that may be
provided by Parent or Purchaser for use in the Proxy Statement, the Schedule
14D-9 or the Other Filings, and neither the Offer Documents nor the Schedule
14D-1, shall, at the time filed with the SEC or any other Governmental Entity,
and, in the case of the Proxy Statement, at the time mailed to the Company's
stockholders, at the time of the Stockholders' Meeting or at the Effective Time,
contain any untrue statement of a material fact or omit to state any material
fact required to be stated therein or necessary in order to make the statements
therein, in light of the circumstances under which they are made, not
misleading. Notwithstanding the foregoing, neither Parent nor Purchaser makes
any representation or warranty with respect to any information provided or that
may be provided by the Company specifically for use in such documents. The
Schedule 14D-1 and the Offer Documents will comply as to form in all material
respects with the provisions of the Exchange Act and the rules and regulations
thereunder.

      SECTION 5.5 Financing. Parent or Purchaser will have available to it at
the time required the funds necessary to consummate the Merger and the
transactions contemplated hereby.

      SECTION 5.6 Brokers. Except for Credit Suisse First Boston Corporation,
whose fees will be paid by Parent, none of Parent, Purchaser, any of their
Subsidiaries, or any of their respective officers, directors or employees has
employed any broker or finder or incurred any liability for any brokerage fees,
commissions or finder's fees in connection with the transactions contemplated by
this Agreement.

                                   ARTICLE VI

                                    COVENANTS


                                       19
<PAGE>

      SECTION 6.1 Conduct of Business of the Company. Except as expressly
contemplated by this Agreement or with the prior written consent of Parent,
during the period from the date of this Agreement to the Effective Time, the
Company will, and will cause each of its Subsidiaries to, conduct its operations
only in the ordinary and usual course of business consistent with past practice
and will use its reasonable best efforts, and will cause each of its
Subsidiaries to use its reasonable best efforts, to preserve intact the business
organization of the Company and each of its Subsidiaries, to keep available the
services of its and their present officers and key employees, and to preserve
the good will of those having business relationships with it. Without limiting
the generality of the foregoing, and except as otherwise expressly contemplated
by this Agreement, the Company will not, and will not permit any of its
Subsidiaries to, prior to the Effective Time, without the prior written consent
of Parent:

      (a) adopt any amendment to its Certificate of Incorporation or By-laws or
comparable organizational documents;

      (b) except for issuances of capital stock of the Company's Subsidiaries to
the Company or a wholly-owned Subsidiary of the Company, issue, reissue, pledge
or sell, or authorize the issuance, reissuance, pledge or sale of (i) additional
shares of capital stock of any class, or securities convertible into,
exchangeable for or evidencing the right to substitute for, capital stock of any
class, or any rights, warrants, options, calls, commitments or any other
agreements of any character, to purchase or acquire any capital stock or any
securities or rights convertible into, exchangeable for, or evidencing the right
to subscribe for, capital stock, or (ii) any other securities in respect of, in
lieu of, or in substitution for, Shares outstanding on the date hereof;

      (c) declare, set aside or pay any dividends or other distribution (whether
in cash, securities or property or any combination thereof) in excess of the
regular quarterly dividend in an amount equal to the last paid regular quarterly
cash dividend paid by the Company which would normally be paid approximately
three months after such last paid regular quarterly dividend was paid, if any
such dividends are declared and paid;

      (d) split, combine, subdivide, reclassify or redeem, purchase or otherwise
acquire, or propose to redeem or purchase or otherwise acquire, any shares of
its capital stock, or any of its other securities; (e) except for (i) increases
in salary and wages granted to officers and employees of the Company or its
Subsidiaries in conjunction with promotions or other changes in job status or
normal compensation reviews (within the amounts projected in the Company's 1998
operating plan previously provided to Parent) in the ordinary course of business
consistent with past practice, or (ii) increases in salary, wages and benefits
to employees of the Company pursuant to collective bargaining agreements in
effect on the date hereof, increase the compensation or fringe benefits payable
or to become payable to its directors, officers or employees (whether from the
Company or any of its Subsidiaries), or pay or award any benefit not required by
any existing plan or arrangement (including, without limitation, the granting of
stock options, stock appreciation rights, shares of restricted stock or
performance units) or grant any additional severance or termination pay to
(other than as required by existing agreements or policies listed on Schedule
4.12(i) hereto), or enter into any employment or severance agreement with, any
director, officer or other employee of the Company or any of its Subsidiaries
or, except pursuant to arrangements disclosed in Schedule 4.12(i), establish,
adopt, enter into, amend, accelerate any rights or benefits or 


                                       20
<PAGE>

waive any performance or vesting criteria under any collective bargaining,
bonus, profit sharing, thrift, compensation, stock option, restricted stock,
pension, retirement, savings, welfare, deferred compensation, "golden
parachute", employment, termination, severance or other employee benefit plan,
agreement, trust, fund, policy or arrangement for the benefit or welfare of any
directors, officers or current or former employees (any of the foregoing being
an "Employee Benefit Arrangement"), except in each case to the extent required
by applicable law or regulation; provided, however, that nothing herein will be
deemed to prohibit the payment of benefits as they become payable;

      (f) acquire, sell, lease or dispose of any assets or securities which are
material to the Company and its Subsidiaries, or enter into any commitment to do
any of the foregoing or enter into any material commitment or transaction, other
than transactions between a wholly owned Subsidiary of the Company and the
Company or another wholly owned Subsidiary of the Company;

      (g) (i) incur, assume or pre-pay any long-term debt or incur or assume any
short-term debt, (ii) assume except in the ordinary course of business
consistent with past practice, guarantee, endorse or otherwise become liable or
responsible (whether directly, contingently or otherwise) for the obligations of
any other person or (iii) make any advances except in the ordinary course of
business consistent with past practice (other than advances to Salomon Smith
Barney required under a letter Agreement between Salomon Smith Barney and the
Company dated February 24, 1998), loans or capital contributions to, or
investments in, any other person (except for investments in short term interest
bearing instruments purchased with excess cash of the Company, and for loans,
advances, capital contributions or investments between any wholly owned
Subsidiary of the Company and the Company or another wholly owned Subsidiary of
the Company);

      (h) settle or compromise any material suit or claim or material threatened
suit or claim;

      (i) other than in the ordinary course of business consistent with past
practice, (i) modify, amend or voluntarily terminate any contract, (ii) waive,
release, relinquish or assign any contract (or any rights of the Company or any
of its Subsidiaries thereunder), right or claim, or (iii) cancel or forgive any
indebtedness owed to the Company or any of its Subsidiaries except for any
indebtedness relating to goods properly returned to the Company;

      (j) make any tax election not required by law or settle or compromise any
tax liability, in either case that is material to the Company and its
Subsidiaries;

      (k) make any material change, other than in the ordinary course of
business and consistent with past practice or as required by applicable law,
regulation or change in generally accepted accounting principles, applied by the
Company (including tax accounting principles);

      (l) release any person or entity from, or waive any provision of, any
standstill agreement to which it is a party or any confidentiality agreement
between it and another person or entity; or

      (m) agree in writing or otherwise to take any of the foregoing actions
prohibited under Section 6.1 or any action which would cause any representation
or warranty in this Agreement to be or become untrue or incorrect in any
material respect.


                                       21
<PAGE>

      SECTION 6.2 Access to Information. From the date of this Agreement until
the Effective Time, the Company will, and will cause its Subsidiaries, and each
of their respective officers, directors, employees, counsel, advisors and
representatives (collectively, the "Company Representatives"), to give Parent
and Purchaser and their respective officers, employees, counsel, advisors and
representatives (collectively, the "Parent Representatives") reasonable access,
during normal business hours, to the offices and other facilities and to the
books and records of the Company and its Subsidiaries and will cause the Company
Representatives and the Company's Subsidiaries to furnish Parent, Purchaser and
Parent Representatives to the extent available with such financial and operating
data and such other information with respect to the business and operations of
the Company and its Subsidiaries as Parent and Purchaser may from time to time
reasonably request. Parent will comply with the terms of the Confidentiality
Agreement (as hereinafter defined).

      SECTION 6.3 Reasonable Best Efforts. Subject to the terms and conditions
herein provided and to applicable legal requirements, each of the parties hereto
agrees to use its reasonable best efforts to take, or cause to be taken, all
action, and to do, or cause to be done, and to assist and cooperate with the
other parties hereto in doing, as promptly as practicable, all things necessary,
proper or advisable under applicable laws and regulations to ensure that the
conditions set forth in Annex I and Article VII are satisfied, to remove any
injunctions or other impediments or delays, legal or otherwise and to consummate
and make effective the transactions contemplated by this Agreement.

      In addition, if at any time prior to the Effective Time any event or
circumstance relating to either the Company or Parent and/or Purchaser or any of
their respective subsidiaries, should be discovered by the Company or Parent, as
the case may be, which should be set forth in the Offer Documents, the Proxy
Statement, the Other Filings, Schedule 14D-1 or Schedule 14D-9, the discovering
party will promptly inform the other parties of such event or circumstance. If
at any time after the Effective Time any further action is necessary or
desirable to carry out the purposes of this Agreement, including the execution
of additional instruments, the proper officers and directors of each party to
this Agreement shall take all such necessary or desirable action.

      SECTION 6.4 Consents.

      (a) Each of the parties will, and will cause its Subsidiaries to, use its
reasonable best efforts to obtain as promptly as practicable all Consents of any
Governmental Entity or any other public or private person required in connection
with, and waivers of any Violations that may be caused by, the consummation of
the transactions contemplated by this Agreement.

      (b) The Company shall obtain as promptly as practicable either a letter of
Non-Applicability from the New Jersey Department of Environmental Protection
indicating that the transactions contemplated hereby do not trigger the
Industrial Site Recovery Act or a Negative Declaration letter indicating that no
remedial actions have to be taken at the New Jersey warehouse in connection with
the transactions contemplated hereby.

      (c) Each of the Company and Parent shall use its reasonable best efforts
to file as soon as practicable notifications under the HSR Act and to respond as
promptly as practicable to any inquiries received from the Federal Trade
Commission and the Antitrust Division of the Department of Justice for
additional information or documentation and to respond as promptly as
practicable to all inquiries and 


                                       22
<PAGE>

requests received from any State Attorney General or other Governmental Entity
in connection with antitrust matters. Each of the Company and Parent shall
further take all reasonable actions necessary to file any other forms or
notifications which may be required by any foreign Governmental Entity and to
obtain any approvals which may be required in connection therewith.

      (d) In furtherance and not in limitation of the foregoing, each of Parent
and the Company shall use its reasonable best efforts to resolve such
objections, if any, as may be asserted with respect to the transactions
contemplated by this Agreement under any antitrust, competition or trade
regulatory laws, rules or regulations of any domestic or foreign government or
Governmental Entity or any multinational authority ("Antitrust Laws"); provided,
however, that nothing in this Agreement shall require, or be construed to
require, Purchaser or any of its affiliates to proffer to, or agree to, sell or
hold separate and agree to sell, before or after the Effective Time, any
material assets, businesses, or interest in any assets or businesses of
Purchaser, the Company or any of their respective affiliates (or to consent to
any sale, or agreement to sell, by the Company of any of its material assets or
businesses) or to agree to any material changes or restrictions in the
operations of any such assets or businesses.

      (e) Any party hereto shall promptly inform the others of any material
communication from the United States Federal Trade Commission, the Department of
Justice or any other domestic or foreign government or governmental or
multinational authority regarding any of the transactions contemplated by this
Agreement. If any party or any affiliate thereof receives a request for
additional information or documentary material from any such government or
authority with respect to the transactions contemplated by this Agreement, then
such party will endeavor in good faith to make, or cause to be made, as soon as
reasonably practicable and after consultation with the other party, an
appropriate response in compliance with such request. Parent will advise the
Company promptly in respect of any understandings, undertakings or agreements
(oral or written) which Parent proposes to make or enter into with the Federal
Trade Commission, the Department of Justice or any other domestic or foreign
government or governmental or multinational authority in connection with the
transactions contemplated by this Agreement.

      SECTION 6.5 Public Announcements. The mutual press release with respect to
the execution of this Agreement shall be a joint press release acceptable to
Parent and the Company. Thereafter, so long as this Agreement is in effect,
neither Parent and Purchaser, on the one hand, nor the Company, on the other,
shall issue any press release or otherwise make any public statement with
respect to the transactions contemplated by this Agreement without prior
consultation with the other party, except as may be required by law or as
contemplated by the first clause of Section 6.8(a)(ii) (it being understood and
agreed that the Company intends to file a Current Report on Form 8-K with
respect to the transaction contemplated hereby promptly after the date hereof).

      SECTION 6.6 Indemnification.

      (a) From and after the date hereof, Parent and Purchaser shall indemnify
and hold harmless each person who is, or has been at any time prior to the date
hereof or who becomes prior to the Effective Time, an officer, director or
employee of the Company or any of its Subsidiaries (collectively, the
"Indemnified Parties" and individually, the "Indemnified Party") against all
losses, liabilities, expenses, claims or damages in connection with any claim,
suit, action, proceeding or investigation based in whole or in part on the fact
that such Indemnified Party is or was a director, officer or employee of the
Company


                                       23
<PAGE>

or any of its Subsidiaries and arising out of acts or omissions occurring prior
to and including the Effective Time (including but not limited to the
transactions contemplated by this Agreement) to the fullest extent permitted by
the GCL, for a period of not less than six years following the Effective Time;
provided, however, that in the event any claim or claims are asserted or made
within such six-year period, all rights to indemnification in respect of any
such claim or claims shall continue until final disposition of any and all such
claims.

      (b) Parent shall cause the Certificate of Incorporation and By-Laws of the
Surviving Corporation and its Subsidiaries to include provisions for the
limitation of liability of directors and indemnification of the Indemnified
Parties to the fullest extent permitted under applicable law and shall not
permit the amendment of such provisions in any manner adverse to the Indemnified
Parties, as the case may be, without the prior written consent of such persons,
for a period of six years from and after the date hereof.

      (c) Without limitation of the foregoing, in the event any such Indemnified
Party is or becomes involved in any capacity in any action, proceeding or
investigation in connection with any matter, including, without limitation, the
transactions contemplated by this Agreement, occurring prior to, and including,
the Effective Time, Parent will pay as incurred such Indemnified Party's legal
and other expenses (including the cost of any investigation and preparation)
incurred in connection therewith, subject to the provision by such Indemnified
Party of an undertaking to reimburse such payments in the event of a final
determination by a court of competent jurisdiction that such Indemnified Party
is not entitled thereto. Subject to the undertaking to reimburse referred to in
the previous sentence, Parent shall pay all expenses, including attorneys' fees,
that may be incurred by any Indemnified Party in enforcing the indemnity and
other obligations provided for in this Section 6.6 or any action involving an
Indemnified Party resulting from the transactions contemplated by this
Agreement.

      (d) Any determination to be made as to whether any Indemnified Party has
met any standard of conduct imposed by law shall be made by legal counsel
reasonably acceptable to such Indemnified Party, Parent and the Surviving
Corporation, retained at Parent's and the Surviving Corporation's expense.

      (e) This Section 6.6 is intended to benefit the Indemnified Parties and
their respective heirs, executors and personal representatives and shall be
binding on the successors and assigns of Parent, Purchaser and the Surviving
Corporation.

      SECTION 6.7 Notification of Certain Matters. Parent and the Company shall
promptly notify each other of (a) the occurrence or non-occurrence of any fact
or event which would be reasonably likely (i) to cause any representation or
warranty contained in this Agreement to be untrue or inaccurate in any material
respect at any time from the date hereof to the Effective Time or (ii) to cause
any material covenant, condition or agreement under this Agreement not to be
complied with or satisfied in all material respects and (b) any failure of the
Company or Parent, as the case may be, to comply with or satisfy any covenant,
condition or agreement to be complied with or satisfied by it hereunder in any
material respect; provided, however, that no such notification shall affect the
representations or warranties of any party or the conditions to the obligations
of any party hereunder.

      SECTION 6.8 No Solicitation.


                                       24
<PAGE>

      (a) The Company and its Subsidiaries shall not, and the Company and its
Subsidiaries shall ensure that their respective officers, directors and
consultants (including, but not limited to, investment bankers, attorneys and
accountants) and will use its best efforts to ensure that its employees,
representatives and agents do not, directly or indirectly, encourage, solicit,
participate in or initiate discussions or negotiations with, or provide any
information to, any corporation, partnership, person or other entity or group
(other than Purchaser, any of its affiliates or representatives) concerning any
proposal or offer to acquire all or a substantial part of the business or
properties of the Company or any of its Subsidiaries or any capital stock of the
Company or any of its Subsidiaries, whether by merger, tender offer, exchange
offer, sale of assets or similar transaction involving the Company or any
Subsidiary, division or operating or principal business unit of the Company (an
"Acquisition Proposal"), except that nothing contained in this Section 6.8 or
any other provision hereof shall prohibit the Company or the Company's Board
from (i) taking and disclosing to the Company's stockholders a position with
respect to a tender or exchange offer by a third party pursuant to Rules 14d-9
and 14e-2 promulgated under the Exchange Act, or (ii) making such disclosure to
the Company's stockholders as, in the good faith judgment of the Board, after
receiving advice from Company counsel, is required under applicable law;
provided that the Company may not, except as permitted by Section 6.8(b),
withdraw or modify its position with respect to the Offer or the Merger or
approve or recommend, or propose to approve or recommend any Acquisition
Proposal, or enter into any agreement with respect to any Acquisition Proposal.
Except as permitted by Section 6.8(b), the Company shall, and shall cause each
of its Subsidiaries to, immediately cease and cause to be terminated any
existing activities, discussions or negotiations by the Company, any of its
Subsidiaries or any officer, director, employee or affiliate of, or investment
banker, attorney, accountant or other advisor or representative of, the Company
or any of its Subsidiaries with parties conducted heretofore with respect to any
of the foregoing.

      (b) Notwithstanding the foregoing, the Company may furnish information
concerning the Company and its Subsidiaries to any corporation, partnership,
person or other entity or group pursuant to appropriate confidentiality
agreements with terms substantially similar to those contained in the
Confidentiality Agreement, and may negotiate and participate in discussions and
negotiations with such entity or group concerning an Acquisition Proposal if (i)
such entity or group, which has not been solicited by or on behalf of the
Company after the date hereof, has submitted a bona fide written proposal to the
Company relating to the acquisition of all or substantially all of the business
or properties of the Company and its subsidiaries or the acquisition of all of
the capital stock of the Company with respect to which the Board concludes in
good faith, after consulting with a nationally recognized investment banking
firm (including but not limited to Salomon Smith Barney), (A) the proposal is
more favorable to the Company's stockholders (in their capacities as
stockholders), from a financial point of view, than the Offer and the Merger and
(B) the bidder is fully capable of completing the transaction in accordance with
the terms of such proposal, and (ii) in the good faith opinion of the Board of
Directors of the Company, only after receipt of written advice from legal
counsel to the Company, the failure to provide such information or access or to
engage in such discussions or negotiations would cause the Board of Directors to
violate its fiduciary duties to the Company's stockholders under applicable law
(an Acquisition Proposal which satisfies clauses (i) and (ii) being referred to
herein as a "Superior Proposal"). The Company shall provide reasonable notice to
Purchaser to the effect that it has received an Acquisition Proposal, including
its terms and conditions (but excluding the identity of the party or parties
making such Acquisition Proposal, unless the terms and conditions of such
Acquisition Proposal contains a purchase price that includes stock of such party
or parties). At any time after 48 hours following notification to Purchaser of


                                       25
<PAGE>

the Company's intent to do so (which notification shall include the identity of
the bidder and the material terms and conditions of the proposal) and if the
Company has otherwise complied with the terms of this Section 6.8(b), the Board
of Directors may withdraw or modify its approval or recommendation of the Offer
and may cause the Company to enter into an agreement with respect to a Superior
Proposal, provided it shall concurrently with entering into such agreement pay
or cause to be paid to Purchaser the Termination Fee (as defined below) plus any
amount payable at the time for reimbursement of expenses pursuant to Section
8.3(b). If the Company shall have notified Purchaser of its intent to enter into
an agreement with respect to a Superior Proposal in compliance with the
preceding sentence and has otherwise complied with such sentence, the Company
may enter into an agreement with respect to such Superior Proposal (with the
bidder and on terms no less favorable than those specified in such notification
to Purchaser) after the expiration of such 48 hour period.

                                   ARTICLE VII

                    CONDITIONS TO CONSUMMATION OF THE MERGER

      SECTION 7.1 Conditions to Each Party's Obligation to Consummate the
Merger. The respective obligations of Parent, Purchaser and the Company to
consummate the Merger and the transactions contemplated hereby are subject to
the satisfaction, at or before the Effective Time, of each of the following
conditions:

      (a) Stockholder Approval. If required by the GCL, the stockholders of the
Company shall have duly approved the transactions contemplated by this
Agreement.

      (b) Injunctions, Illegality. The consummation of the Merger shall not be
restrained, enjoined or prohibited by any order, judgment, decree, injunction or
ruling of a court of competent jurisdiction or any Governmental Entity and there
shall not have been any statute, rule or regulation enacted, promulgated or
deemed applicable to the Merger by any Governmental Entity which prevents the
consummation of the Merger.

      (c) Purchase of Shares. Parent and/or Purchaser shall have purchased all
Shares validly tendered and not withdrawn pursuant to the Offer; provided,
however, that this condition shall not be applicable to the obligations of
Parent or Purchaser if Parent and/or Purchaser fails to purchase Shares tendered
pursuant to the Offer in violation of the terms of this Agreement or the Offer.

                                  ARTICLE VIII

                         TERMINATION; AMENDMENTS; WAIVER

      SECTION 8.1 Termination. This Agreement may be terminated and the Merger
contemplated hereby may be abandoned at any time prior to the Effective Time,
notwithstanding approval thereof by the stockholders of the Company (with any
termination by Parent also being an effective termination by Purchaser):

      (a) by mutual consent of Parent and the Company;


                                       26
<PAGE>

      (b) by Parent or the Company:

      (i) if any court or Governmental Entity shall have issued an order, decree
or ruling or taken any other action (which order, decree, ruling or other action
the parties hereto shall use their reasonable best efforts to lift) restraining,
enjoining or otherwise prohibiting the Merger and such order, decree, ruling or
other action shall have become final and nonappealable; or

      (ii) if (x) the Offer shall have expired without any Shares being
purchased therein or (y) Purchaser shall not have accepted for payment all
Shares tendered pursuant to the Offer by March 31, 1999; provided, however, that
the right to terminate this Agreement under this Section 8.1(b)(ii) shall not be
available to any party whose failure to fulfill any obligation under this
Agreement has been the cause of, or resulted in, the failure of Purchaser, to
purchase the Shares pursuant to the Offer on or prior to such date; or

      (iii) if the Supervisory Board of Wolters Kluwer nv shall not have
approved the transactions contemplated hereby by June 10, 1998.

      (c) by the Company:

            (i) if Parent and/or Purchaser fails to commence the Offer as
provided in Section 1.1 hereof; provided, that the Company may not terminate
this Agreement pursuant to this Section 8.1(c)(i) if the Company is at such time
in breach of its obligations under this Agreement such as to cause a Material
Adverse Effect on the Company;

            (ii) in connection with entering into a definitive agreement in
accordance with Section 6.8(b), provided it has complied with all provisions of
such section, including the notice provisions therein, and that it makes
simultaneous payment of the Termination Fee plus any amounts then due as a
reimbursement of expenses; or

            (iii) if Parent or Purchaser shall have made a material
misrepresentation or have breached in any material respect any of their
respective representations, covenants or other agreements contained in this
Agreement, which breach (a) cannot be or has not been cured, in all material
respects, within 30 days after the giving of written notice to Parent or
Purchaser, as applicable, and (b) limits or restricts the ability of Parent or
Purchaser to consummate the transactions contemplated hereby.

      (d) by Parent:

            (i) if prior to the purchase of Shares pursuant to the Offer, the
Company shall have breached any representation, warranty, covenant or other
agreement contained in this Agreement which (A) would give rise to the failure
of a condition set forth in paragraph (e) or (f) of Annex I hereto and (B)
cannot be or has not been cured, in all material respects, within 30 days after
the giving of written notice to the Company; or

            (ii) if any event set forth in paragraph (d) of Annex I hereto shall
have occurred.

      SECTION 8.2 Effect of Termination. In the event of the termination of this
Agreement


                                       27
<PAGE>

pursuant to Section 8.1, this Agreement shall forthwith become void and have no
effect, without any liability on the part of any party or its directors,
officers or stockholders, other than the provisions of this Section 8.2, Section
8.3 and the last sentence of Section 6.2, which shall survive any such
termination. Nothing contained in this Section 8.2 shall relieve any party from
liability for any breach of this Agreement or the Confidentiality Agreement.

      SECTION 8.3 Fees and Expenses.

      (a) Except as contemplated by this Agreement, each party hereto shall bear
its own expenses and costs in connection with this Agreement and the
transactions contemplated hereby.

      (b) If

            (w) the Company shall terminate this Agreement pursuant to Section
8.1(c)(ii) hereof,

            (x) Parent shall terminate this Agreement pursuant to Section
8.1(d)(ii) hereof,

            (y) either the Company or Parent terminates this Agreement pursuant
to Section 8.1(b)(ii) and (a) prior thereto there shall have been publicly
announced another Acquisition Proposal (provided, however, that solely for
purposes of this clause (a), the term Acquisition Proposal shall not include (1)
the purchase of less than 5% of any class or series of capital stock of the
Company if such purchase does not involve an offer to acquire additional shares
of capital stock of the Company that could cause any person, entity or "group"
(as defined in Section 13(d)(3) of the Exchange Act), other than Purchaser or
its affiliates or any group of which any of them is a member, to beneficially
own 5% or more of any such class or series or (2) any purchase of 5% or more of
any class or series of capital stock of the Company which can properly be
reported on a Schedule 13G and (b) an Acquisition Proposal pursuant to which any
Person acquires all or a substantial part of the business or properties of the
Company or any of its Subsidiaries, any of the capital stock (or securities
exercisable for or convertible into such capital stock) of any of the
Subsidiaries of the Company or any capital stock (or securities exercisable for
or convertible into such capital stock) of the Company which represents 20% or
more of the equity interest or voting power of the Company shall be consummated
on or prior to March 31, 1999, or

            (z) Parent shall terminate this Agreement pursuant to Section
8.1(d)(i) hereof and an Acquisition Proposal pursuant to which any Person
acquires all or a substantial part of the business or properties of the Company
or any of its Subsidiaries, any of the capital stock (or securities exercisable
for or convertible into such capital stock) of any of the Subsidiaries of the
Company or any capital stock (or securities exercisable for or convertible into
such capital stock) of the Company which represents 20% or more of the equity
interest or voting power of the Company shall be consummated on or prior to
March 31, 1999,

then, the Company shall pay to Purchaser an amount equal to Seven Million Five
Hundred Thousand Dollars ($7,500,000)(the "Termination Fee"), plus an amount
equal to Purchaser's actual documented reasonable out-of-pocket fees and
expenses (including, without limitation, reasonable legal, investment banking,
financing commitment fees and commercial banking fees and expenses) incurred by
Purchaser and Parent in connection with the due diligence investigation, the
Offer, the Merger, this Agreement and 


                                       28
<PAGE>

the consummation of the transactions contemplated hereby (the "Reimbursable
Expenses"), which shall be payable by wire transfer of same day funds to an
account designated by Purchaser. The Company shall also be obligated to pay to
Purchaser the Reimbursable Expenses in such manner if Parent shall terminate
this Agreement pursuant to Section 8.1(d)(i) hereof (regardless of whether an
Acquisition Proposal is consummated thereafter). The Termination Fee and
Purchaser's good faith estimate of its Reimbursable Expenses shall be paid
concurrently with any such termination, together with delivery of a written
acknowledgment by the Company of its obligation to reimburse Purchaser for its
actual expenses in excess of such estimated expenses payment, except that the
Termination Fee and such expenses shall be payable in connection with a
termination described in clauses (y) or (z) above upon the consummation of an
Acquisition Proposal referenced in such clauses. All fees and expenses paid
pursuant to this Section shall constitute liquidated damages and the Company
shall have no further liability to Purchaser or Parent under this Agreement
after the payment of such fees and expenses, provided that nothing in this
sentence shall affect any liability the Company may have to Purchaser or Parent
under Stock Purchase Agreements (if any) and the Option Agreement.

      SECTION 8.4 Amendment. This Agreement may be amended by Parent and the
Company at any time before or after any approval of this Agreement by the
stockholders of the Company but, after any such approval, no amendment shall be
made which decreases the Purchase Price or changes the form thereof without the
approval of such stockholders. This Agreement may not be amended except by an
instrument in writing signed on behalf of all the parties.

      SECTION 8.5 Extension; Waiver. At any time prior to the Effective Time,
any party hereto may (i) extend the time for the performance of any of the
obligations or other acts of any other party hereto, (ii) waive any inaccuracies
in the representations and warranties contained herein by any other party or in
any document, certificate or writing delivered pursuant hereto by any other
party or (iii) waive compliance with any of the agreements of any other party or
with any conditions to its own obligations. Any agreement on the part of any
party to any such extension or waiver shall be valid only if set forth in an
instrument in writing signed on behalf of such party.

                                   ARTICLE IX

                                  MISCELLANEOUS

      SECTION 9.1 Non-Survival of Representations and Warranties. The
representations and warranties made in this Agreement shall not survive beyond
the Effective Time. The covenants and other agreements contained herein shall
survive in accordance with their respective terms.

      SECTION 9.2 Entire Agreement; Assignment.

      (a) This Agreement (including the documents and the instruments referred
to herein) and the letter agreement between Salomon Smith Barney, on behalf of
the Company, and Wolters Kluwer U.S. Corporation, on its own behalf and for
Parent and its other affiliates, dated April 6, 1998 (the "Confidentiality
Agreement"), constitute the entire agreement and supersede all prior agreements
and understandings, both written and oral, among the parties with respect to the
subject matter hereof and thereof.

      (b) Neither this Agreement nor any of the rights, interests or obligations
hereunder will be assigned by any of the parties hereto (whether by operation of
law or otherwise) without the prior written consent of the other party (except
that Parent may assign its rights and Purchaser may assign its rights, 


                                       29
<PAGE>

interest and obligations to any affiliate or direct or indirect subsidiary of
Parent without the consent of the Company). Subject to the preceding sentence,
this Agreement will be binding upon, inure to the benefit of and be enforceable
by the parties and their respective successors and assigns.

      SECTION 9.3 Validity. The invalidity or unenforceability of any provision
of this Agreement shall not affect the validity or enforceability of any other
provision of this Agreement, each of which shall remain in full force and
effect.

      SECTION 9.4 Notices. All notices, requests, claims, demands and other
communications hereunder shall be in writing and shall be deemed to have been
duly given when delivered in person, by overnight courier or facsimile to the
respective parties as follows:

      If to Parent or Purchaser:

            Kluwer Boston, Inc.
            c/o Kluwer Academic Publishers bv
            Spuiboulevard 50, 311GR Dordrecht
            3300 AZ Dordrecht, The Netherlands
            Attention: Jeffrey K. Smith
            Fax #: (011)(31)(78) 639-2268

      with a copy to:

            Wolters Kluwer U.S. Corporation
            161 North Clark Street, 48th Floor
            Chicago, Illinois  60601-3221
            Attention: Bruce C. Lenz
            Fax #: (312) 425-02[cad 220]33 or 0234

      and to:

            Pryor Cashman Sherman & Flynn LLP
            410 Park Avenue
            New York, New York  10022
            Attention: Arnold J. Schaab, Esq.
            Fax #: (212) 326-0806

      If to the Company:

            Plenum Publishing Corporation
            233 Spring Street
            New York, New York 10013
            Attention: Martin E. Tash
            Fax #:  (212) 463-0742

      with copies to:

            Bressler, Amery & Ross, P.C.
            17 State Street


                                       30
<PAGE>

            New York, New York 10004
            Attention: Bernard Bressler

            Fax #: (212) 425-9337

or to such other address as the person to whom notice is given may have
previously furnished to the other in writing in the manner set forth above
(provided that notice of any change of address shall be effective only upon
receipt thereof).

      SECTION 9.5 Governing Law. This Agreement shall be governed by and
construed in accordance with the laws of the State of Delaware, regardless of
the laws that might otherwise govern under applicable principles of conflicts of
laws thereof.

      SECTION 9.6 Consent to Jurisdiction; Waiver of Immunities. The Company,
Parent and Purchaser irrevocably submit to the jurisdiction of any Delaware
state or federal court thereof in any action or proceeding arising out of or
relating to this Agreement, and the Company, Parent and Purchaser hereby
irrevocably agree that all claims in respect of such action or proceeding may be
heard and determined in such Delaware court or in such federal court. Parent and
Purchaser hereby irrevocably appoint The Corporation Trust Company (the "Parent
Process Agent"), with an office on the date hereof at Corporation Trust Center,
1209 Orange Street, Wilmington, Delaware, as its agent to receive on behalf of
Parent or Purchaser service of copies of the summons and complaint and any other
process which may be served in any such action or proceeding. Such service may
be made by mailing or delivering a copy of such process to Parent or Purchaser
in care of Parent Process Agent at Parent Process Agent's above address, and
Parent and/or Purchaser hereby irrevocably authorize and direct Parent Process
Agent to accept such service on their behalf. The Company hereby irrevocably
appoints The Corporation Trust Company (the "Company Process Agent"), with an
office on the date hereof at Corporation Trust Center, 1209 Orange Street,
Wilmington, Delaware, as its agent to receive on behalf of the Company service
of copies of the summons and complaint and any other process which may be served
in any such action or proceeding. Such service may be made by mailing or
delivering a copy of such process to the Company in care of the Company Process
Agent at the Company Process Agent's above address, and the Company hereby
irrevocably authorizes and directs the Company Process Agent to accept such
service on its behalf. As an alternative method of service, the Company, Parent
and Purchaser also irrevocably consent to the service of any and all process in
any such action or proceeding by the mailing of copies of such process to the
respective party at its address specified in Section 9.4. The Company, Parent
and Purchaser agree that a final judgment in any such action or proceeding shall
be conclusive and may be enforced in other jurisdictions by suit on the judgment
or in any other manner provided by law.

      SECTION 9.7 Descriptive Headings. The descriptive headings and captions
herein are inserted for convenience of reference only and are not intended to be
part of or to affect the meaning or interpretation of this Agreement.

      SECTION 9.8 Counterparts. This Agreement may be executed in two or more
counterparts, each of which shall be deemed to be an original, but all of which
shall constitute one and the same agreement.

      SECTION 9.9 Parties in Interest. This Agreement shall be binding upon and
inure solely to the benefit of each party hereto, and, except with respect to
Sections 2.9 and 6.6, nothing in this Agreement, express or implied, is intended
to confer upon any other person any rights or remedies of any nature whatsoever
under or by reason of this Agreement.


                                       31
<PAGE>

      SECTION 9.10 Certain Definitions. As used in this Agreement:

      (a) the term "Affiliate," as applied to any person, shall mean any other
person directly or indirectly controlling, controlled by, or under common
control with, that person. For the purposes of this definition, "Control"
(including, with correlative meanings, the terms "controlling," "controlled by"
and "under common control with"), as applied to any person, means the
possession, directly or indirectly, of the power to direct or cause the
direction of the management and policies of that person, whether through the
ownership of voting securities, by contract or otherwise;

      (b) the term "Person" shall include individuals, corporations,
partnerships, trusts, other entities and groups (which term shall include a
"group" as such term is defined in Section 13(d)(3) of the Exchange Act); and

      (c) the term "Subsidiary", "Subsidiaries" or "subsidiaries" means, with
respect to Parent, the Company or any other person, any corporation,
partnership, joint venture or other legal entity of which Parent, the Company or
such other person, as the case may be (either alone or through or together with
any other subsidiary), owns, directly or indirectly, stock or other equity
interests the holders of which are generally entitled to more than 50% of the
vote for the election of the board of directors or other governing body of such
corporation or other legal entity.

      SECTION 9.11 Specific Performance. The parties hereto agree that
irreparable damage would occur in the event that any of the provisions of this
Agreement were not performed in accordance with their specific terms or were
otherwise breached. It is accordingly agreed that the parties shall be entitled
to an injunction or injunctions to prevent breaches of this Agreement and to
enforce specifically the terms and provisions hereof in any court of the United
States or any state having jurisdiction, this being in addition to any other
remedy to which they are entitled at law or in equity.

                                    * * * * *

      IN WITNESS WHEREOF, each of the parties has caused this Agreement and Plan
of Merger to be executed on its behalf by its respective officer thereunto duly
authorized, all as of the day and year first above written.

                                KLUWER BOSTON, INC.


                                By: /s/ Jeffrey K. Smith
                                   -------------------------------
                                   Name:  Jeffrey K. Smith
                                   Title: President


                                PPC ACQUISITION CORP.


                                By: /s/ Jeffrey K. Smith
                                   -------------------------------
                                   Name:  Jeffrey K. Smith
                                   Title: President


                                   32
<PAGE>

                                PLENUM PUBLISHING CORPORATION

                                By: /s/ Martin E. Tash
                                   -------------------------------
                                   Name:  Martin E. Tash
                                   Title: President and Chairman of the Board


                                       33
<PAGE>

                                     ANNEX I

      Certain Conditions of the Offer. Notwithstanding any other provisions of
the Offer, and in addition to (and not in limitation of) Purchaser's rights to
extend and amend the Offer at any time in its sole discretion (subject to the
provisions of the Merger Agreement), Purchaser shall not be required to accept
for payment or, subject to any applicable rules and regulations of the SEC,
including Rule 14e-l(c) under the Exchange Act (relating to Purchaser's
obligation to pay for or return tendered Shares promptly after termination or
withdrawal of the Offer), pay for, and may delay the acceptance for payment of
or, subject to the restriction referred to above, the payment for, any tendered
Shares, and may terminate or amend the Offer as to any Shares not then paid for,
if (i) any applicable waiting period under the HSR Act has not expired or
terminated, (ii) the Minimum Condition has not been satisfied, or (iii) at any
time on or after the date of the Merger Agreement and before the time of
acceptance for payment for any such Shares, any of the following events shall
have occurred:

      (a) there shall be threatened or pending any suit, action or proceeding by
any Governmental Entity against Purchaser, Parent, the Company or any Subsidiary
of the Company (i) seeking to prohibit or impose any material limitations on
Purchaser's or Parent's ownership or operation (or that of any of their
respective Subsidiaries or affiliates) of all or a material portion of their or
the Company's businesses or assets (or that of any of its Subsidiaries), or to
compel Purchaser or Parent or their respective Subsidiaries and affiliates to
dispose of or hold separate any material portion of the business or assets of
the Company or Parent and their respective Subsidiaries, in each case taken as a
whole, (ii) challenging the acquisition by Purchaser or Parent of any Shares
under the Offer, seeking to restrain or prohibit the making or consummation of
the Offer or the Merger or the performance of any of the other transactions
contemplated by the Agreement or the Stock Purchase Agreements, or seeking to
obtain from the Company, Purchaser or Parent any damages that are material in
relation to the Company and its Subsidiaries taken as a whole, (iii) seeking to
impose material limitations on the ability of Purchaser, or render Purchaser
unable, to accept for payment, pay for or purchase some or all of the Shares
pursuant to the Offer and the Merger or (iv) seeking to impose material
limitations on the ability of Purchaser or Parent effectively to exercise full
rights of ownership of the Shares, including, without limitation, the right to
vote the Shares purchased by it on all matters properly presented to the
Company's stockholders or there shall be pending any suit, action or proceeding
by any Governmental Entity against Purchaser, Parent, the Company or any
Subsidiary of the Company which is reasonably likely to have a Material Adverse
Effect on the Company;

      (b) there shall be any statute, rule, regulation, judgment, order or
injunction enacted, entered, enforced, promulgated, or deemed applicable,
pursuant to an authoritative interpretation by or on behalf of a Government
Entity, to the Offer or the Merger, or any other action shall be taken by any
Governmental Entity, other than the application to the Offer or the Merger of
applicable waiting periods under HSR Act, that is reasonably likely to result,
directly or indirectly, in any of the consequences referred to in clauses (i)
through (iv) of paragraph (a) above;

      (c) there shall have occurred any events after the date of the Agreement
which have or will have a Material Adverse Effect on the Company;

      (d) (i) the Board of Directors of the Company or any committee thereof
shall have withdrawn or modified in a manner adverse to Parent or Purchaser its
approval or recommendation of the Offer, the Merger or the Agreement, or
approved or recommended any Acquisition Proposal or (ii) the Company shall have
entered into any agreement with respect to any Superior Proposal in accordance
with Section 6.8(b) of the Agreement;


                                       34
<PAGE>

      (e) the representations and warranties of the Company set forth in the
Agreement shall not be true and correct, in each case (i) as of the date
referred to in any representation or warranty which addresses matters as of a
particular date, or (ii) as to all other representations and warranties, as of
the date of the Agreement and as of the scheduled expiration of the Offer unless
the inaccuracies without giving effect to any materiality or material adverse
effect qualifications or materiality exceptions contained therein under such
representations and warranties, taking all the inaccuracies under all such
representations and warranties together in their entirety, do not result in
Material Adverse Effect on the Company;

      (f) the Company shall have failed to perform any obligation or to comply
with any agreement or covenant to be performed or complied with by it (i) under
Section 6.1 or 6.8 of the Agreement or (ii) under any other agreement or
covenant to be performed or complied with by it under the Agreement, unless the
failure to so perform or comply would not have a Material Adverse Effect on the
Company;

      (g) the Agreement shall have been terminated in accordance with its terms;

      The foregoing conditions are for the benefit of Parent and Purchaser, may
be asserted by Parent or Purchaser regardless of the circumstances giving rise
to any such conditions and may be waived by Parent or Purchaser in whole or in
part at any time and from time to time in their reasonable discretion, in each
case, subject to the terms of the Merger Agreement. The failure by Parent or
Purchaser at any time to exercise any of the foregoing rights shall not be
deemed a waiver of any such right and each such right shall be deemed an ongoing
right which may be asserted at any time and from time to time.

      The capitalized terms used in this Annex I shall have the meanings set
forth in the Agreement to which it is annexed, except that the term "Merger
Agreement" shall be deemed to refer to the Agreement to which this Annex I is
appended.


                                       35
<PAGE>

                                  SCHEDULE 4.8

                                MATERIAL CHANGES

      After March 31, 1998, the Company realized losses of approximately $3.4
million dollars as a result of liquidating its securities portfolio. The only
remaining investments are 34,825 shares of Gradco Systems, Inc. and an
investment of $1.1 million dollars at cost in Tutor Time Learning Systems stock
and a note receivable.


                                       36
<PAGE>

                                  SCHEDULE 4.11

                                   LITIGATION

      None.


                                       37
<PAGE>

                                SCHEDULE 4.12(a)

                             EMPLOYEE BENEFIT PLANS

1.    Profit Sharing Plan (effective 1/1/89, as amended on 3/20/92, 3/17/93,
      5/16/94 and 12/13/94).

2.    Incentive Compensation Plan for Executive Officers and Key Employees.

3.    Employee Medical Benefit Plan managed by Corporate Healthcare Financing,
      Inc.

4.    Group Insurance Program providing term life and accidental death and
      dismemberment coverage - Fortis Benefits Insurance Company (Policy 65121).

5.    See Schedule 4.12(i) for "golden parachute" agreements.

6.    Sick pay policy for hourly personnel - 7 days per year.

7.    Severance pay: seven months to one year - 1 week; one year or more - 2
      weeks.

8.    Travel Insurance - $500,000 Hartford Insurance Co. Policy No. 12ETB108204,
      Expires May 1, 2000.


                                       38
<PAGE>

                                SCHEDULE 4.12(i)

                        EMPLOYMENT/TERMINATION AGREEMENTS

      1.    Second Amended Contingent Compensation Agreements dated 8/1/96 with
            the following persons:

                  a.    Martin E. Tash;
                  b.    Mark Shaw;
                  c.    Harry Allcock;
                  d.    Ken Derham;
                  e.    Ghanshyam Patel.

      2.    Contingent Compensation Contracts dated 8/1/96 with the following
            persons:

                  a.    John Hwang;
                  b.    Carol Bischoff;
                  c.    Tom Mulak.


                                       39
<PAGE>

                                SCHEDULE 4.12(j)

                                   LABOR UNION

      At the Company warehouse in Edison, New Jersey the hourly workers are
represented by Local 29, Retail/Wholesale & Deparment Store Union, AFL-CIO.


                                       40
<PAGE>

                                SCHEDULE 4.14(b)

                                    LICENSES

1.    Translation Rights Agreement dated March 3, 1998 between Plenum Publishing
      Corporation ("Plenum") and Editoriale Armenia (granting license to publish
      Tao of Immunology).

2.    Firstsearch Electronic Collections Online Agreement dated September 2,
      1997 between Plenum and OCLC Online Computer Library Center, Incorporated
      (granting right to make journals available online).

3.    Agreement dated June 17, 1997 between Plenum and Blackwells (granting
      access to CatchWord journals).

4.    General Agreement dated April 16, 1997 between Plenum and UMI Company
      (granting license to reproduce and distribute various works).

5.    Rights Agreement dated January 1, 1997 between Plenum and The British
      Library Board (granting license to use material in journals and other
      works).

6.    Agreement dated October 31, 1996 between Plenum and Kenneth Marshall
      (granting license to publish paperback editions of A Sexual Odyssey).

7.    Comprehensive Publisher Photocopy Agreement dated June 28, 1995 between
      Plenum and Copyright Clearance Center, Inc. (granting right to reproduce
      and distribute substantially all print publications of Plenum).

8.    Agreement dated March 30, 1990 between Plenum and University Microfilms,
      Inc. (granting license to reproduce and distribute various works in
      microform).

9.    Agreement dated April 10, 1989 between Plenum and MacMillan Book Clubs,
      Inc. (granting book club rights in Comprehensive Handbook of Cognitive
      Therapy).

10.   Agreement dated February 6, 1986 between Plenum and the Institute for
      Scientific Information, Inc. (granting license reproduce and distribute
      two journals).

11.   License Agreement between Plenum and Information Access Company (granting
      license reproduce and distribute two journals).

12.   Miscellaneous agreements in which Plenum grants permission to reprint a
      certain number of copies of material owned by Plenum.

13.   License Agreement dated January 21, 1994 between IFI/Plenum Data
      Corporation ("IFI") and The American Chemical Society (granting license to
      utilize computer databases).

14.   Database License Agreement dated November 1, 1991 between Maxwell Online,
      Inc. and IFI (granting license to utilize computer databases).


                                       41
<PAGE>

                                  SCHEDULE 4.16

                              ENVIRONMENTAL MATTERS

      Set forth below is a summary of the file maintained by the New Jersey
Department of Environmental Protection ("NJDEP") with respect to real property
located at 200 and 220 McGaw Drive, Edison Township, New Jersey, which Plenum
purchased on November 16, 1990. The NJDEP file was generated in connection with
the action taken by a prior owner, L. Perrigo Company ("Perrigo"), to comply
with the requirements of the Environmental Cleanup Responsibility Act ("ECRA").
This Act was subsequently amended and is now known as the Industrial Site
Recovery Act ("ISRA").

      Prior Owners and Operators

      On December 31, 1983, Albert Frassetto purchased the property from I.C.E.
Associates. He owned the property until it was sold to Plenum Publishing
Corporation ("Plenum"). The site consists of a warehousing space and two office
areas located on the main floor and on a mezzanine. From September 1979 through
August 1994 First National State Bank leased the mezzanine area for office
space. Thereafter, from September 1984 through December 1989 the New Jersey
Teachers Academy leased this space.

      ECRA

      The requirements of ECRA are triggered when an "industrial establishment"
terminates, transfers or closes its business activities. Industrial
establishments are defined in the statute as places of business which utilize
hazardous substances and have an Standard Industrial Classification Code ("SIC")
set out in the statute. The statute covers all manufacturing operations and
certain other activities. Perrigo intially took the position that the property
was not subject to the requirements of ECRA because of the owner's SIC code.
However, this analysis was incorrect because the SIC code of the property is
based upon the business operations undertaken at the facility. In this case,
NJDEP decided that the SIC code for Perrigo, the tenant was 51, an ECRA subject
activity.

      In July 1990, Perrigo submitted a request for an Administrative Consent
Order ("ACO") allowing the termination of activities before the ECRA
investigation and cleanup was completed. The company agreed to establish a
$500,000 financial assurance to secure its cleanup obligation.

      In October 1990, Perrigo submitted its General Information Submission
("GIS") and Site Evaluation Submission ("SES") forms to the NJDEP. These forms
generally discussed the business activities conducted at the site. In addition,
they showed that the primary environmental concern for the property was the
existence of two 4,000 gallon underground storage tanks ("USTs"). These USTs
were used for storage of No. 2 heating oil. No other environmental concerns
existed because the facility was used primarily for storage of finished and
packaged goods.

      Perrigo hired an environmental consultant to handle the closure of the
USTs and post-excavation sampling. In its report, the consultant stated that no
holes were noted in the tanks after they were removed from the ground. Further,
all post-excavation soil samples were well below the NJDEP's existing cleanup
limits. Based on this information, no further action was approved for these
areas of concern.


                                       42
<PAGE>

      In a Report of Inspection, the NJDEP case manager also requested further
information concerning a hole observed in the facility's wall and floor drains.
Perrigo was able to resolve these issues by showing that the hole was related to
stormwater runoff from the roof, and the floor drains emptied to the sanitary
sewer line.

      Sale of Property to Plenum

      In October 1990, Frassetto advised the NJDEP that a contract to sell the
property to Plenum had been executed. An amendment to the ACO was executed. This
amendment authorized the transaction to close. However, no substantive cleanup
requirements were imposed because of its execution.

      On March 26, 1991, Perrigo submitted a Negative Declaration Affidavit
stating that the cleanup for the property was complete and performed in
accordance with NJDEP regulatory requirements. This Negative Declaration was
approved by NJDEP on April 3, 1991. With the issuance of this letter, the ECRA
review was closed.


                                       43
<PAGE>

                                  SCHEDULE 4.17

                                    INSURANCE



                                                     Policy Number 488-30-26-58

- -------------------------------------------------------------------------------
                          COMMON POLICY DECLARATIONS
                               PREMIUM STATEMENT
- -------------------------------------------------------------------------------

NAMED INSURED:                              PRODUCER:
PLENUM PUBLISHING CORP.                        HARVEY DANN CO INC
(SEE AIL 03 #2)                                 122 EAST 42ND STREET
233 SPRING STREET                               SUITE 1013
NEW YORK, NY 10013                              NEW YORK, NY

                                                                          10168

Premium Statement for the period from 05/15/97 to 05/15/98

This policy consists of the following coverage parts for which a premium is 
indicated. This premium may be subject to adjustment.

<TABLE>
<CAPTION>
           COVERAGE SECTION                                        PREMIUM
- --------------------------------------         --------------------------------------------------
                                               At Inception    1st Anniversary    2nd Anniversary
                                               ------------    ---------------    ---------------
<S>                                            <S>              <C>               <C>
Commercial Property Coverage Part                   $22.128

Commercial General Liability Coverage Part          $17.253

Commercial Crime Coverage Part         

Commercial Auto Coverage Part                        $6.272

Commercial Umbrella Coverage Part                    $7.302

Commercial Inland Marine Coverage Part               $1.540

Boiler and Machinery Coverage Part



LIBEL COVERAGE PART                                 $21.000





            Total Advance Premium                   $75.495
                                               ------------    ---------------    ---------------
STATE CHARGES                                       $96.35
  (SEE AIL 03 07 86 $003)        

</TABLE>

- -------------------------------------------------------------------------------
                             SCHEDULE OF PAYMENTS
- -------------------------------------------------------------------------------
SEE CONTINUATION OF PREMIUM STATEMENT. AIL03. FOR SCHEDULE OF PAYMENTS

C P W

AIL 02 07 95                         INSURED                 PREMIUM STATEMENT

                                       44

<PAGE>


                                                     Policy Number 298-50-09-89

- -------------------------------------------------------------------------------
                          COMMON POLICY DECLARATIONS
                               PREMIUM STATEMENT
- -------------------------------------------------------------------------------

NAMED INSURED:                              PRODUCER:
PLENUM PUBLISHING CORP.                        HARVEY DANN CO INC
(SEE AIL 03 #2)                                 122 EAST 42ND STREET
233 SPRING STREET                               SUITE 1013
NEW YORK, NY 10013                              NEW YORK, NY

                                                                          10168

Premium Statement for the period from 05/15/97 to 05/15/98

This policy consists of the following coverage parts for which a premium is 
indicated. This premium may be subject to adjustment.

<TABLE>
<CAPTION>
           COVERAGE SECTION                                        PREMIUM
- --------------------------------------         --------------------------------------------------
                                               At Inception    1st Anniversary    2nd Anniversary
                                               ------------    ---------------    ---------------
<S>                                            <S>              <C>               <C>
Commercial Property Coverage Part

Commercial General Liability Coverage Part

Commercial Crime Coverage Part

Commercial Auto Coverage Part                     $2.874

Commercial Umbrella Coverage Part

Commercial Inland Marine Coverage Part

Boiler and Machinery Coverage Part




                     Total Advance Premium        $2.874
                                               ------------    ---------------    ---------------
NY VEHICLE FEE                                    $1.00

</TABLE>

- -------------------------------------------------------------------------------
                             SCHEDULE OF PAYMENTS
- -------------------------------------------------------------------------------

C P W

AIL 02 07 86                         INSURED                 PREMIUM STATEMENT

                                       45


<PAGE>

Centennial      WORKERS COMPENSATION AND EMPLOYERS LIABILITY
Commercial                   INSURANCE POLICY
Insurance Company
NCII #12149                  Information Page

Rewrite of No.                                          Policy Number
Renewal of No.  401-51-41-93                             401-70-91-24
 
                                                     (INTRASTATE G16908)
Item 1. INSURED. The Insured and Malling Address:        ID # 910743759
PLENUM PUBLISHING CORP.                                 FEIN 135648711
233 SPRING STREET
NEW YORK, NY 10013                          Other workplaces not shown at left:


/ / INDIVIDUAL         / / PARTNERSHIP        /X/ CORPORATION         / / OTHER
- -------------------------------------------------------------------------------
Item 2. POLICY PERIOD. From: May 15, 1997    To: May 15, 1998  12:01 A.M. 
                                             STANDARD TIME AT THE SCHEDULED 
                                             MAILING ADDRESS
- -------------------------------------------------------------------------------
Item 3. COVERAGE

A.  Workers Compensation Insurance: Part One of the policy applies to the 
Workers Compensation Law of the states listed here:

       DELAWARE                 NEW JERSEY               NEW YORK
       NORTH CAROLINA

B.  Employers Liability Insurance: Part Two of the policy applies to work in 
    each state listed in item 3A.

                The Limits of our liability under Part Two are:

Bodily injury by Accident   Bodily Injury by Disease    Bodily Injury by Disease
 $100,000 each accident      $500,000 policy limit       $100,000 each employee

C.  Other States Insurance:  Part Three of the policy applies to the states, 
    if any, listed here: All states except Nevada, North Dakota, Ohio, 
    Washington, West Virginia and states designated in Item 3.A. of the 
    Information Page.

D.  This policy includes these endorsements and schedules: SEE G1690B 
    SCHEDULE OF ENDORSEMENTS

- -------------------------------------------------------------------------------
Item 4. PREMIUM.  The premium for this policy will be determined by our 
                  Manuals of Rules, Classifications, Rates and Rating Plans. 
                  All information required below is subject to verification 
                  and change by audit.
- -------------------------------------------------------------------------------
<TABLE>
<CAPTION>
                                                                              Price Per    
                                        Code           Total Estimated        %100 of      Estimated ANNUAL  
 Classifications                         No.             ANNUAL                                 Products     
- -----------------------------------------------------------------------------------------------------------
<S>                                   <C>              <C>                   <C>            <C>
See Extension of information Page                                                                38,172.0
Surcharges and Assessments                                                                        3,796.0
and/or Filing Fees (SEE G16908)
Expense Constant Charge                                                                           INCLUDE
- -----------------------------------------------------------------------------------------------------------
Minimum            Interim            Deposit                                   Total          
Premium $850 (NJ)  Adjustments        Premium                                 Estimated         $41,968.0
                                                                                Cost
- -----------------------------------------------------------------------------------------------------------
</TABLE>
Representative         Agent or Broker  HARVEY DANN CO INC
                       Office Address
                                       122 EAST 42ND STREET 
                                       SUITE 1013
                City, State, Zip Code  NEW YORK, NY          10168
- -------------------------------------------------------------------------------
DATE OF ISSUE: JPS: 05/27/97           SERVICING OFFICE: NEW YORK
/ / This is a Three Year Fixed Rate Plicy

RENEWED BY POLICY NUMBER
                         CPW     Corporated by /s/ Dennis J. Sellers
- ------------------------                       ---------------------------------
                                                Authorized Signature     Date

2Q 44191-1 (11/96)    Copyright 1987 National Council on Compensation Insurance
WC 00 00 01A                               INSURED

                                        46

<PAGE>

                                                           


                            STOCK PURCHASE AGREEMENT

      Stock Purchase Agreement (this "Agreement"), dated as of June 10, 1998,
between PPC Acquisition Corp. ("Purchaser") and Martin Tash and Arlene Tash
(together called "Shareholder").

      WHEREAS, Shareholder owns (beneficially) 423,485 shares of common stock,
par value $.10 per share ("Common Stock") of Plenum Publishing Corp. (the
"Company")(including shares as to which Shareholder has voting power pursuant to
the terms of the Company Qualified Profit Sharing Plan) all as set forth on
Schedule A hereto (the "Shares").

      WHEREAS, concurrently herewith, Kluwer Boston Inc. ("Parent") and
Purchaser, a wholly owned subsidiary of Parent, are entering into an agreement
and plan of merger with the Company, dated as of June 10, 1998 (the "Merger
Agreement"), pursuant to which Purchaser has agreed to make a cash tender offer
(the "Offer") for, among other things, all outstanding shares of Common Stock of
the Company at $73.50 per share (or any higher price paid in the Offer, the
"Offer Price"), net to the seller in cash, to be followed by a merger of
Purchaser with and into the Company (the "Merger"); and

      WHEREAS, as a condition to the willingness of Purchaser and Parent to
enter into the Merger Agreement, Purchaser, whose performance hereunder is
guaranteed by Parent, has required that Shareholder agree, and in order to
induce Purchaser and Parent to enter into the Merger Agreement, Shareholder has
agreed, among other things, (i) to sell the Shares; (ii) to tender the Shares
into the Offer; (iii) to appoint Purchaser as Shareholder's proxy to vote the
Shares under certain circumstances, and (iv) with respect to certain questions
put to stockholders of the Company for a vote, to vote the Shares, in each case,
in accordance with the terms and conditions of this Agreement.

      NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained herein and other good and valuable consideration, the adequacy of
which is hereby acknowledged, and intending to be legally bound hereby, the
parties hereto agree as follows:

1. Purchase and Sale of Shares.

      1.1 Tender of Shares; Purchase of Shares.

            (a) Shareholder agrees to tender and sell to Purchaser all of the
Shares pursuant to the terms of the Offer. Shareholder agrees that Shareholder
shall deliver to the depository for the Offer for receipt prior to the
Expiration Date (as defined in the Offer) of the Offer, either a letter of
transmittal together with the certificates for the Shares, if available, or a
"Notice of Guaranteed Delivery", if the Shares are not available. Unless an
election is made by Purchaser under Section 1.1(b), Shareholder agrees not to
withdraw any Shares tendered into the Offer. Upon such tender Shareholder will
be relieved of any obligation under Sec. 1.1(b) hereof.
<PAGE>

            (b) Upon the election of Purchaser on the terms and subject to the
conditions set forth in this Agreement, on (and assuming the occurrence of) the
Closing Date (as defined herein), Purchaser will purchase from the Shareholder,
and the Shareholder will sell and transfer to the Purchaser, all of the Shares,
free and clear of all mortgages, pledges, security interest, encumbrances,
liens, options, debts, charges, claims and restrictions of any kind, at a
purchase price per share equal to the Offer Price.

      1.2 Conditions to the Closing.

            Subject to the provisions of the first sentence of Section 1.3
hereof, the obligations of the parties to consummate the transactions
contemplated by Section 1.1(b) hereof are subject to the following conditions:
(a) any waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of
1976, as amended (the "HSR Act") applicable to the delivery of the Shares and
the consummation of the Offer shall have expired or been terminated; and (b)
there shall be no preliminary or permanent injunction or other order by any
court of competent jurisdiction restricting, preventing or prohibiting the
delivery of the Shares. Purchaser and Shareholder shall each promptly after the
date hereof make such filings and provide such information as may be required
under the HSR Act with respect to the sale of the Shares.

      1.3 Closing.

            Subject to the conditions contained in this Agreement and subject to
Sections 1.4 through 1.8, the closing of the transactions contemplated by
Section 1.1(b) hereof (the "Closing") shall occur at a site designated by
Purchaser simultaneously with the acceptance by Purchaser of the shares of
Common Stock validly tendered and not withdrawn pursuant to the terms of the
Offer in accordance with the terms and conditions of the Offer and the Merger
Agreement (the "Closing Date"). At the Closing and subject to the conditions
contained in this Agreement, Purchaser hereby directs Shareholder to deliver to
Purchaser a certificate or certificates evidencing the Shares, each such
certificate being duly endorsed in blank and accompanied by such stock powers
and such other documents as may be necessary in Purchaser's judgment to transfer
record ownership of the Shares into Purchaser's name on the stock transfer books
of the Company, and Purchaser will purchase the Shares at a purchase price equal
to the Offer Price. All payments made by Purchaser to Shareholder pursuant to
this Section 1.3 shall be made by wire transfer of immediately available funds
to an account designated by Shareholder, or by certified bank check payable to
Shareholder, in an amount equal to the sum of the product of (i) the Offer Price
and (ii) the total number of Shares delivered at the Closing.

      1.4 Stock Option.

            Effective upon expiration or termination of the Offer for the
reasons set forth in Section 1.5 below, Purchaser shall have an irrevocable
option (the "Stock Option") exercisable on the terms and conditions set forth in
Section 1.5 below to purchase the Shares, at a purchase 


                                       -2-
<PAGE>

price equal to the Offer Price.

      1.5 Termination or Expiration of Offer and Exercise of Stock Option.

            (a)(i) If the Offer is terminated by Purchaser for the reasons set
forth in paragraph (d) of Annex I to the Merger Agreement or (ii) in the case of
the expiration of the Offer, if the Offer expires without the purchase of Shares
thereunder and either without satisfaction of the Minimum Condition (as defined
in the Merger Agreement) or after the occurrence of circumstances giving rise to
a right of termination by Purchaser for the reasons set forth in paragraph (d)
of Annex I to the Merger Agreement, in each case without any violation of the
Offer or the Merger Agreement by Purchaser or Parent, then the Stock Option may
be exercised by Purchaser, in whole and for all of Shareholder's Shares but not
in part or for less than all of Shareholder's Shares. Notice of exercise may be
given at any time during the period (the "Exercise Period") commencing on the
date on which the Offer is terminated or expires (under the circumstances
provided in this Section 1.5) and ending on March 31, 1999, whichever is later.
In addition, Purchaser may also exercise the Stock Option if the Merger
Agreement shall terminate by reason of the Company's exercise of its termination
rights pursuant to Section 8.1(c)(ii) of the Merger Agreement, whereupon the
Exercise Period shall commence on the date such termination rights are exercised
and end on March 31, 1999, whichever is later.

            (b) In the event Purchaser wishes to exercise the Stock Option,
Purchaser shall send a written notice (an "Exercise Notice") during the Exercise
Period to the Shareholder specifying that Purchaser shall purchase the Shares
held by Shareholder and a date, which shall be a business day, and a place,
which shall be in the city of New York, for the closing of such purchase (the
"Stock Option Closing").

            (c) Upon receipt of the Exercise Notice, Shareholder shall be
obligated to deliver to Purchaser a certificate or certificates representing the
Shares held by Shareholder (or to direct the depositary for the Offer to so
deliver such certificates or certificates), in accordance with the terms of this
Agreement, on the later of the date specified in such Exercise Notice or the
first business day on which the conditions specified in Section 1.6 shall be
satisfied. The date specified in such Exercise Notice may be as early as one
business day after the date of such Exercise Notice but shall not be later than
five (5) business days after the later of (i) the date of such Exercise Notice,
or (ii) the date all conditions under Section 1.6 are satisfied.

      1.6 Conditions to Delivery of the Shares.

            The obligation of the Shareholder to deliver, and of the Purchaser
to pay for, the Shares upon exercise of the Stock Option is subject to the
following conditions:

            (a) All waiting periods under the Hart-Scott-Rodino Antitrust
Improvements Act of 1976, as amended, applicable to the exercise of the Stock
Option and the delivery of the Shares shall have expired or been terminated; and


                                      -3-
<PAGE>

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

      1.7 Stock Option Closing.

            At the Stock Option Closing, the Shareholder will deliver to
Purchaser a certificate or certificates evidencing the Shares owned by
Shareholder, each such certificate being duly endorsed in blank and accompanied
by such stock powers and such other documents as may be necessary in Purchaser's
judgment to transfer record ownership of the Shares into Purchaser's name on the
stock transfer books of the Company, and Purchaser will purchase the delivered
Shares at the Offer Price. All payments made by Purchaser to Shareholder
pursuant to this Section 1.7 shall be made by wire transfer of immediately
available funds or by certified bank check payable to Shareholder, in an amount
equal to the product of (a) the Offer Price and (b) the Shares delivered by
Shareholder in respect of the Stock Option Closing.

      1.8 Adjustments Upon Changes in Capitalization.

            In the event of any change in the number of issued and outstanding
shares of Common Stock by reason of any stock dividend, subdivision, merger,
recapitalization, combination, conversion or exchange of shares, or any other
change in the corporate or capital structure of the Company (including, without
limitation, the declaration of payment of an extraordinary dividend of cash or
securities) which would have the effect of diluting or otherwise adversely
affecting Purchaser's rights and privileges under this Agreement, the number and
kind of the shares and the consideration payable in respect to the Shares shall
be appropriately and equitably adjusted to restore to Purchaser its rights and
privileges under this Agreement. Without limiting the scope of the foregoing, in
any such event, at the option of Purchaser, the Stock Option shall represent the
right to purchase, in addition to the number and kind of Shares which Purchaser
would be entitled to purchase pursuant to the immediately preceding sentence,
whatever securities, cash or other property the Shares subject to the Stock
Option shall have been converted into or otherwise exchanged for, together with
any securities, cash or other property which shall have been distributed with
respect to such Shares.


                                      -4-
<PAGE>

2. Representations and Warranties of Shareholder.

      Shareholder hereby represents and warrants to Purchaser as follows:

      2.1 Title.

            Shareholder is the owner (both beneficially and of record, or
beneficially as respects the interest of Shareholder in shares held in the
Profit Sharing Plan) of the Shares as set forth on Schedule A. Except for the
Shares Shareholder is not the record or beneficial owner of, and does not have
any other rights of any nature to acquire any additional shares of, any shares
of capital stock of the Company. Shareholder will deliver in accordance with the
terms of this Agreement, all of the Shares, free and clear of all security
interests, liens, claims, pledges, options, restrictions, rights of first
refusal, agreements, limitations on Shareholder's voting rights, charges and
other encumbrances of any nature whatsoever, and, except as provided in this
Agreement, Shareholder has not appointed or granted any proxy, which appointment
or grant is still effective, with respect to any of the Shares. The Shareholder
has sole power of disposition (or to direct disposition with respect to Shares
in the Profit Sharing Plan) with respect to all of the Shares and sole voting
power with respect to the matters set forth in Section 6 hereof with respect to
the Shares.

      2.2 Authority Relative to This Agreement.

            Shareholder has all necessary power and authority to execute and
deliver this Agreement, to perform Shareholder's obligations hereunder and to
consummate the transactions contemplated hereby. This Agreement has been duly
and validly executed and delivered by Shareholder and, assuming the due
authorization, execution and delivery by Purchaser, constitutes a legal, valid
and binding obligation of Shareholder enforceable against Shareholder in
accordance with its terms.

      2.3 No Conflict.

            The execution and delivery of this Agreement by Shareholder does
not, and the performance of this Agreement by Shareholder will not, (a) except
for any filings required under the HSR Act and for requirements of federal and
state securities laws, require any consent, approval, authorization or permit
of, or filing with or notification to, any governmental or regulatory authority,
domestic or foreign, or (b) conflict with, violate or result in any breach of or
constitute a default under (or an event which with notice or lapse of time or
both would become a default under) any agreement, judgment, injunction, order,
law, rule, regulation, decree or arrangement to which Shareholder is a party or
is bound.


                                      -5-
<PAGE>

      2.4 Brokers.

            Except for Salomon Smith Barney, whose fees will be paid by the
Company and a true and correct copy of whose engagement letter has been provided
by the Company, no broker, finder or investment banker is entitled to any
brokerage, finder's or other fee or commission in connection with the
transactions contemplated hereby based upon arrangements made by or on behalf of
Shareholder or the Company.

3. Representations and Warranties of Purchaser and Parent.

      3.1 Authority Relative to This Agreement.

            Purchaser and Parent have all necessary power and authority to
execute and deliver this Agreement, to perform its obligations hereunder and to
consummate the transactions contemplated hereby. The execution and delivery of
this Agreement by Purchaser and the consummation by Purchaser of the
transactions contemplated hereby have been duly and validly authorized by all
necessary corporate action on the part of Purchaser and Parent. This Agreement
has been duly and validly executed and delivered by Purchaser and Parent as
Guarantor, assuming the due authorization, execution and delivery by
Shareholder, constitutes a legal, valid and binding obligation of Purchaser and
Parent, enforceable against Purchaser and Parent in accordance with its terms.

      3.2 No Conflict.

            The execution and delivery of this Agreement by Purchaser and Parent
does not, and the performance of this Agreement by Purchaser and Parent will
not, (a) except for any filings required under the HSR Act and for requirements
of federal and state securities laws, require any consent, approval,
authorization or permit of, or filing with or notification to, any governmental
or regulatory authority, domestic or foreign, (b) conflict with or violate the
certificate of incorporation or bylaws of Purchaser or Parent, (c) conflict
with, violate or result in any breach of or constitute a default under (or an
event which with notice or lapse of time or both would become a default under)
any agreement, judgment, injunction, order, law, rule, regulation, decree or
arrangement applicable to Purchaser or Parent or by which any property or asset
of Purchaser or Parent is bound or affected, other than, in the case of clause
(c), any such conflicts, violations, breaches or defaults that, individually or
in the aggregate, would not materially impair the ability of Purchaser or Parent
to perform its obligations hereunder.

      3.3 Brokers.

            Except for Credit Suisse First Boston, whose fees will be paid by
Purchaser, no broker, finder or investment banker is entitled to any brokerage,
finder's or other fee or commission from Shareholder in connection with the
transactions contemplated hereby based upon arrangements made by or on behalf of
Purchaser.


                                      -6-
<PAGE>

      3.4 Investment Intent.

            Purchaser hereby represents that any securities it purchases
pursuant to this Agreement are being purchased for its own account for
investment and not with a view to, or for sale in connection with, any public
distribution thereof.

4. Covenant of Shareholder.

      No Solicitation of Transactions. Shareholder and his affiliates shall not,
and Shareholder and his affiliates shall use their best efforts to ensure that
Shareholder's representatives and agents (including, but not limited to,
investment bankers, attorneys and accountants) and his affiliates' officers,
directors, employees, representatives and agents do not, directly or indirectly,
encourage, solicit, participate in or initiate discussions or negotiations with,
or provide any information to, any corporation, partnership, person or other
entity or group (other than Purchaser or any of its affiliates or
representatives) concerning any proposal or offer to acquire all or a
substantial part of the business or properties of the Company or any of its
subsidiaries, whether by merger, tender offer, exchange offer, sale of assets or
similar transaction involving the Company or any subsidiary, division or
operating or principal business unit of the Company (an "Acquisition Proposal"),
except that the provisions of this Section 4 shall not restrict the
Shareholder's ability to act in such Shareholder's capacity as a director of the
Company in accordance with Section 6.8 of the Merger Agreement. Shareholder
shall immediately cease and cause to be terminated any existing activities,
discussions or negotiations by Shareholder or his affiliates or any investment
banker, attorney, accountant or other advisor or representative of Shareholder
or his affiliates with parties conducted heretofore with respect to any of the
foregoing.

5. Additional Covenants of Shareholder.

      5.1 No Disposition. Shareholder hereby covenants and agrees that, except
as contemplated by this Agreement and except pursuant to the Offer, Shareholder
shall not, and shall not offer or agree to, sell, transfer, tender, assign, or
otherwise dispose of, or create or permit to exist any restriction, right of
first refusal, agreement or limitation on Shareholder's voting rights, with
respect to, the Shares now owned or any other shares that may hereafter be
acquired by Shareholder.

      5.2 Compliance of Shareholder with this Agreement. Shareholder shall take
all actions and forbear from all actions, in each case, necessary in order that
(a) all of Shareholder's representations and warranties hereunder are true and
correct and (b) Shareholder fulfills all of its obligations hereunder.


                                      -7-
<PAGE>

6. Voting Agreement; Proxy of Shareholder.

      6.1 Voting Agreement.

            Shareholder hereby agrees that, during the time this Agreement is in
effect, at any meeting of the stockholders of the Company, however called, and
in any action by written consent of the stockholders of the Company, Shareholder
shall, to the extent applicable, (a) vote (or execute a consent in respect of)
all of the Shares in favor of the Merger, the Merger Agreement (as amended from
time to time) and any of the transactions contemplated by the Merger Agreement;
(b) vote (or execute a consent in respect of) the Shares against any action or
agreement that would result in a breach of any covenant, representation or
warranty or any other obligation of the Company under the Merger Agreement; and
(c) vote (or execute a consent in respect of) the Shares against any action or
agreement that would reasonably be expected to impede, interfere with, delay or
attempt to discourage the Offer or the Merger, including, but not limited to:
(i) any extraordinary corporate transaction (other than the Merger), such as a
merger, reorganization, recapitalization or liquidation involving the Company or
any of its Subsidiaries (as defined in the Merger Agreement) or any proposal
made in opposition to or in competition with the Merger; (ii) a sale or transfer
of a material amount of assets of the Company or any of its Subsidiaries; (iii)
any change in the management or board of directors of the Company, except as
otherwise agreed to in writing by Purchaser or Purchaser; (iv) any material
change in the present capitalization or dividend policy of the Company; or (v)
any other material change in the corporate structure or business of the Company
or any of its Subsidiaries.

      6.2 Irrevocable Proxy.

            Shareholder agrees that, in the event Shareholder shall fail to
comply with the provisions of Section 6.1 hereof as determined by Purchaser in
its sole discretion, such failure shall result, without any further action by
Shareholder, in the irrevocable appointment of Purchaser as the attorney and
proxy of Shareholder, with full power of substitution, to vote, and otherwise
act (by written consent or otherwise) with respect to all of the Shares that
Shareholder is entitled to vote at any meeting of stockholders of the Company
(whether annual or special and whether or not an adjourned or postponed meeting)
or consent in lieu of any such meeting or otherwise, on the matters and in the
manner specified in Section 6.1. THIS PROXY AND POWER OF ATTORNEY IS IRREVOCABLE
AND COUPLED WITH AN INTEREST AND IS EXECUTED AND INTENDED TO BE IRREVOCABLE IN
ACCORDANCE WITH THE PROVISIONS OF SECTION 212(e) OF THE DELAWARE GENERAL
CORPORATION LAW ("DGCL"). Shareholder hereby revokes, effective upon the
execution and delivery of the Merger Agreement by the parties thereto, all other
proxies and powers of attorney with respect to the Shares that Shareholder may
have heretofore appointed or granted, and no subsequent proxy or power of
attorney (except in furtherance of Shareholder's obligations under Section 6.1
hereof) shall be given or written consent executed (and if given or executed,
shall not be effective) by Shareholder with respect thereto so long as this
Agreement remains in effect.


                                      -8-
<PAGE>

7. Termination.

      Other than the Stock Option which shall be governed by Section 1.4(a)
hereof, this Agreement shall terminate automatically in the event that the
Merger Agreement is terminated in accordance with the terms and conditions
thereof.

8. Miscellaneous.

      8.1 Expenses.

            All costs and expenses incurred in connection with the transactions
contemplated by this Agreement shall be paid by the party incurring such
expenses.

      8.2 Further Assurances.

            Shareholder and Purchaser shall execute and deliver all such further
documents and instruments and take all such further action as may be necessary
in order to consummate the transactions contemplated hereby.

      8.3 Specific Performance.

            The parties hereto agree that irreparable damage would occur in the
event any provision of this Agreement were not performed in accordance with the
terms hereof and that the parties shall be entitled to specific performance of
the terms hereof, in addition to any other remedy at law or in equity.

      8.4 Entire Agreement.

            This Agreement constitutes the entire agreement between Purchaser
and Shareholder with respect to the subject matter hereof and supersedes all
prior agreements and understandings, both written and oral, between Purchaser
and Shareholder with respect to the subject matter hereof.

      8.5 Assignment.

            This Agreement shall not be assigned by operation of law or
otherwise, except that Purchaser may assign all or any of its rights hereunder
except that such assignment shall not relieve Purchaser of its obligations
hereunder if such assignee does not perform such obligations.


                                      -9-
<PAGE>

      8.6 Parties in Interest.

            This Agreement shall be binding upon, inure solely to the benefit
of, and be enforceable by, the parties hereto and their successors and permitted
assigns. Nothing in this Agreement, express or implied, is intended to or shall
confer upon any other person any right, benefit or remedy of any nature
whatsoever under or by reason of this Agreement.

      8.7 Amendment; Waiver.

            This Agreement may not be amended except by an instrument in writing
signed by the parties hereto. Any party hereto may (a) extend the time for the
performance of any obligation or other act of any other party hereto, (b) waive
any inaccuracy in the representations and warranties contained herein or in any
document delivered pursuant hereto and (c) waive compliance with any agreement
or condition contained herein. Any such extension or waiver shall be valid if
set forth in an instrument in writing signed by the party or parties to be bound
thereby.

      8.8 Severability.

            If any term or other provision of this Agreement is invalid, illegal
or incapable of being enforced by any rule of law, or public policy, all other
conditions and provisions of this Agreement shall nevertheless remain in full
force and effect so long as the economic or legal substance of this Agreement is
not affected in any manner materially adverse to any party. Upon such
determination that any term or other provision is invalid, illegal or incapable
of being enforced, the parties hereto shall negotiate in good faith to modify
this Agreement so as to effect the original intent of the parties as closely as
possible in a mutually acceptable manner in order that the terms of this
Agreement remain as originally contemplated to the fullest extent possible.

      8.9 Notices.

            All notices, requests, claims, demands and other communications
hereunder shall be in writing and shall be deemed to have been duly given when
delivered in person, by overnight courier or facsimile to the respective parties
as follows:

                  If to Purchaser:

                        PPC Acquisition Corp.
                        c/o Kluwer Academic Publishers bv
                        Spuiboulevard 50, 311GR Dordrecht
                        3300 AZ Dordrecht, The Netherlands
                        Attention: Jeffrey K. Smith

                        Fax #: (011)(31)(78) 639-2268


                                      -10-
<PAGE>

                  with a copy to:

                        Wolters Kluwer U.S. Corporation
                        161 North Clark Street
                        48th Floor
                        Chicago, Illinois 60601-3221
                        Attention: Bruce C. Lenz

                        Fax #:  (312) 425-0233

                  and to:

                        Pryor Cashman Sherman & Flynn LLP
                        410 Park Avenue
                        New York, New York 10022
                        Attention: Arnold J. Schaab, Esq.

                        Fax #:  (212) 326-0806

                  if to Shareholder:

                        Martin and Arlene Tash
                        17049 Northway Circle
                        Boca Raton, Florida 33496

                        Fax #:  (561) 852-1559

                  with a copy to:

                        BRESSLER, AMERY & ROSS, P.C.
                        17 State Street
                        New York, New York 10004
                        Attention: Bernard Bressler, Esq.

                        Fax #:  (212) 425-9337

      8.10 Governing Law.

            This Agreement shall be governed by, and construed in accordance
with, the laws of the State of Delaware applicable to contracts executed in and
to be performed in Delaware without regard to any principles of choice of law or
conflicts of law of such State. All actions and proceedings arising out of or
relating to this Agreement shall be heard and determined in any state or federal
court sitting in Delaware. Each of the parties hereto (i) consents to submit
such 


                                      -11-
<PAGE>

party to the personal jurisdiction of any Federal court located in the State of
Delaware or any Delaware state court in the event any dispute arises out of this
Agreement or any of the transactions contemplated hereby, (ii) agrees that such
party will not attempt to deny or defeat such personal jurisdiction by motion or
other request for leave from any such court, (iii) agrees that such party will
not bring any action relating to this Agreement or the transactions contemplated
hereby in any court other than a Federal court sitting in the state of Delaware
or a Delaware state court and (iv) waives any right to trial by jury with
respect to any claim or proceeding related to or arising out of this Agreement
or any of the transactions contemplated hereby.

      8.11 Headings.

            The descriptive headings contained in this Agreement are included
for convenience of reference only and shall not affect in any way the meaning or
interpretation of this Agreement.

      8.12 Counterparts.

            This Agreement may be executed and delivered (including by facsimile
transmission) in one or more counterparts, and by the different parties hereto
in separate counterparts, each of which when as executed and delivered shall be
deemed to be an original but all of which taken together shall constitute one
and the same agreement.


                                      -12-
<PAGE>

      IN WITNESS WHEREOF, each of the parties hereto has caused this Agreement
to be duly executed and delivered as of the date first written above.

                                    PPC ACQUISITION CORP.


                                    By: /s/ Jefrey K. Smith
                                       ----------------------------
                                       Name:  Jeffrey K. Smith
                                       Title: President

                                    Shareholder

                                       /s/ Martin Tash
                                    -------------------------------
                                    Martin Tash

                                       /s/ Arlene Tash
                                    -------------------------------
                                    Arlene Tash


                                      -13-
<PAGE>

      Kluwer Boston, Inc. in consideration of the undertakings hereunder by
Shareholder does hereby guaranty performance of the obligations undertake herein
by Purchaser and to the extent that such guarantee shall relate to the payment
of moneys, such guaranty shall be a guaranty of performance and not a guaranty
of collection.

                                    KLUWER BOSTON, INC.


                                    By: /s/ Jeffrey K. Smith
                                       ----------------------------
                                       Name:  Jeffrey K. Smith
                                       Title: President


                                      -14-
<PAGE>

                                   SCHEDULE A

                             MARTIN AND ARLENE TASH

      Shares Owned Of Record and Beneficially
      By Martin Tash Individually                                       12,920

      Shares Owned In Account Designated For
      Martin Tash In Plenum Publishing Profit
      Sharing Plan                                                     112,336

      Shares Owned Jointly of Record and Beneficially
      By Martin Tash and Arlene Tash                                   298,229
                                                                       -------

                                                                       423,485


<PAGE>

                                                           


                            STOCK PURCHASE AGREEMENT

      Stock Purchase Agreement (this "Agreement"), dated as of June 10, 1998,
between PPC Acquisition Corp. ("Purchaser") and Mark Shaw and Hally Shaw
(together called "Shareholder").

      WHEREAS, Shareholder owns (both beneficially and as trustee FBO u/a Dtd.
8/25/76 FBO Jared Roger Shaw and Scott Harlan Shaw ("Trustee") total of 80,667
shares of common stock, par value $.10 per share ("Common Stock") of Plenum
Publishing Corp. (the "Company") all as set forth on Schedule A hereto (the
"Shares").

      WHEREAS, concurrently herewith, Kluwer Boston Inc. ("Parent") and
Purchaser, a wholly owned subsidiary of Parent, are entering into an agreement
and plan of merger with the Company, dated as of June 10, 1998 (the "Merger
Agreement"), pursuant to which Purchaser has agreed to make a cash tender offer
(the "Offer") for, among other things, all outstanding shares of Common Stock of
the Company at $73.50 per share (or any higher price paid in the Offer, the
"Offer Price"), net to the seller in cash, to be followed by a merger of
Purchaser with and into the Company (the "Merger"); and

      WHEREAS, as a condition to the willingness of Purchaser and Parent to
enter into the Merger Agreement, Purchaser, whose performance hereunder is
guaranteed by Parent, has required that Shareholder agree, and in order to
induce Purchaser and Parent to enter into the Merger Agreement, Shareholder has
agreed, among other things, (i) to sell the Shares; (ii) to appoint Purchaser as
Shareholder's proxy to vote the Shares under certain circumstances, and (iii)
with respect to certain questions put to stockholders of the Company for a vote,
to vote the Shares, in each case, in accordance with the terms and conditions of
this Agreement.

      NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained herein and other good and valuable consideration, the adequacy of
which is hereby acknowledged, and intending to be legally bound hereby, the
parties hereto agree as follows:

1. Purchase and Sale of Shares.

      1.1 Tender of Shares; Purchase of Shares.

            (a) Shareholder agrees to tender and sell to Purchaser all of the
Shares pursuant to the terms of the Offer. Shareholder agrees that Shareholder
shall deliver to the depository for the Offer for receipt prior to the
Expiration Date (as defined in the Offer) of the Offer, either a letter of
transmittal together with the certificates for the Shares, if available, or a
"Notice of Guaranteed Delivery", if the Shares are not available. Unless an
election is made by Purchaser under Section 1.1(b), Shareholder agrees not to
withdraw any Shares tendered into the Offer. Upon such tender Shareholder will
be relieved of any obligation under Sec. 1.1(b) hereof.

            (b) Upon the election of Purchaser on the terms and subject to the
conditions 
<PAGE>

set forth in this Agreement, on (and assuming the occurrence of) the Closing
Date (as defined herein), Purchaser will purchase from the Shareholder, and the
Shareholder will sell and transfer to the Purchaser, all of the Shares, free and
clear of all mortgages, pledges, security interest, encumbrances, liens,
options, debts, charges, claims and restrictions of any kind, at a purchase
price per share equal to the Offer Price.

      1.2 Conditions to the Closing.

            Subject to the provisions of the first sentence of Section 1.3
hereof, the obligations of the parties to consummate the transactions
contemplated by Section 1.1 hereof are subject to the following conditions: (a)
any waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of
1976, as amended (the "HSR Act") applicable to the delivery of the Shares and
the consummation of the Offer shall have expired or been terminated; and (b)
there shall be no preliminary or permanent injunction or other order by any
court of competent jurisdiction restricting, preventing or prohibiting the
delivery of the Shares. Purchaser and Shareholder shall each promptly after the
date hereof make such filings and provide such information as may be required
under the HSR Act with respect to the sale of the Shares.

      1.3 Closing.

            Subject to the conditions contained in this Agreement and subject to
Sections 1.4 through 1.8, the closing of the transactions contemplated by
Section 1.1 hereof (the "Closing") shall occur at a site designated by Purchaser
simultaneously with the acceptance by Purchaser of the shares of Common Stock
validly tendered and not withdrawn pursuant to the terms of the Offer in
accordance with the terms and conditions of the Offer and the Merger Agreement
(the "Closing Date"). At the Closing and subject to the conditions contained in
this Agreement, Purchaser hereby directs Shareholder to deliver to Purchaser a
certificate or certificates evidencing the Shares, each such certificate being
duly endorsed in blank and accompanied by such stock powers and such other
documents as may be necessary in Purchaser's judgment to transfer record
ownership of the Shares into Purchaser's name on the stock transfer books of the
Company, and Purchaser will purchase the Shares at a purchase price equal to the
Offer Price. All payments made by Purchaser to Shareholder pursuant to this
Section 1.3 shall be made by wire transfer of immediately available funds to an
account designated by Shareholder, or by certified bank check payable to
Shareholder, in an amount equal to the sum of the product of (i) the Offer Price
and (ii) the total number of Shares delivered at the Closing.

      1.4 Stock Option.

            Effective upon expiration or termination of the Offer for the
reasons set forth in Section 1.5 below, Purchaser shall have an irrevocable
option (the "Stock Option") exercisable on the terms and conditions set forth in
Section 1.5 below to purchase the Shares, at a purchase price equal to the Offer
Price.

      1.5 Termination or Expiration of Offer and Exercise of Stock Option.


                                      -2-
<PAGE>

            (a)(i) If the Offer is terminated by Purchaser for the reasons set
forth in paragraph (d) of Annex I to the Merger Agreement or (ii) in the case of
the expiration of the Offer, if the Offer expires without the purchase of Shares
thereunder and either without satisfaction of the Minimum Condition (as defined
in the Merger Agreement) or after the occurrence of circumstances giving rise to
a right of termination by Purchaser for the reasons set forth in paragraph (d)
of Annex I to the Merger Agreement, in each case without any violation of the
Offer or the Merger Agreement by Purchaser or Parent, then the Stock Option may
be exercised by Purchaser, in whole and for all of Shareholder's Shares but not
in part or for less than all of Shareholder's Shares. Notice of exercise may be
given at any time during the period (the "Exercise Period") commencing on the
date on which the Offer is terminated or expires (under the circumstances
provided in this Section 1.5) and ending on March 31, 1999, whichever is later.
In addition, Purchaser may also exercise the Stock Option if the Merger
Agreement shall terminate by reason of the Company's exercise of its termination
rights pursuant to Section 8.1(c)(ii) of the Merger Agreement, whereupon the
Exercise Period shall commence on the date such termination rights are exercised
and end on July 1, 1999, whichever is later.

            (b) In the event Purchaser wishes to exercise the Stock Option,
Purchaser shall send a written notice (an "Exercise Notice") during the Exercise
Period to the Shareholder specifying that Purchaser shall purchase the Shares
held by Shareholder and a date, which shall be a business day, and a place,
which shall be in the city of New York, for the closing of such purchase (the
"Stock Option Closing").

            (c) Upon receipt of the Exercise Notice, Shareholder shall be
obligated to deliver to Purchaser a certificate or certificates representing the
Shares held by Shareholder (or to direct the depositary for the Offer to so
deliver such certificates or certificates), in accordance with the terms of this
Agreement, on the later of the date specified in such Exercise Notice or the
first business day on which the conditions specified in Section 1.6 shall be
satisfied. The date specified in such Exercise Notice may be as early as one
business day after the date of such Exercise Notice but shall not be later than
five (5) business days after the later of (i) the date of such Exercise Notice,
or (ii) the date all conditions under Section 1.6 are satisfied.

      1.6 Conditions to Delivery of the Shares.

            The obligation of the Shareholder to deliver, and of the Purchaser
to pay for, the Shares upon exercise of the Stock Option is subject to the
following conditions:

            (a) All waiting periods under the Hart-Scott-Rodino Antitrust
Improvements Act of 1976, as amended, applicable to the exercise of the Stock
Option and the delivery of the Shares shall have expired or been terminated; and

            (b) There shall be no permanent injunction or other order by any
court of competent jurisdiction restricting, preventing or prohibiting the
exercise of the Stock Option or 


                                      -3-
<PAGE>

the delivery of the Shares in respect of such exercise.

      1.7 Stock Option Closing.

            At the Stock Option Closing, the Shareholder will deliver to
Purchaser a certificate or certificates evidencing the Shares owned by
Shareholder, each such certificate being duly endorsed in blank and accompanied
by such stock powers and such other documents as may be necessary in Purchaser's
judgment to transfer record ownership of the Shares into Purchaser's name on the
stock transfer books of the Company, and Purchaser will purchase the delivered
Shares at the Offer Price. All payments made by Purchaser to Shareholder
pursuant to this Section 1.7 shall be made by wire transfer of immediately
available funds or by certified bank check payable to Shareholder, in an amount
equal to the product of (a) the Offer Price and (b) the Shares delivered by
Shareholder in respect of the Stock Option Closing.

      1.8 Adjustments Upon Changes in Capitalization.

            In the event of any change in the number of issued and outstanding
shares of Common Stock by reason of any stock dividend, subdivision, merger,
recapitalization, combination, conversion or exchange of shares, or any other
change in the corporate or capital structure of the Company (including, without
limitation, the declaration of payment of an extraordinary dividend of cash or
securities) which would have the effect of diluting or otherwise adversely
affecting Purchaser's rights and privileges under this Agreement, the number and
kind of the shares and the consideration payable in respect to the Shares shall
be appropriately and equitably adjusted to restore to Purchaser its rights and
privileges under this Agreement. Without limiting the scope of the foregoing, in
any such event, at the option of Purchaser, the Stock Option shall represent the
right to purchase, in addition to the number and kind of Shares which Purchaser
would be entitled to purchase pursuant to the immediately preceding sentence,
whatever securities, cash or other property the Shares subject to the Stock
Option shall have been converted into or otherwise exchanged for, together with
any securities, cash or other property which shall have been distributed with
respect to such Shares.

      1.9 Tender of Shares.

            Upon the request of Purchaser, Shareholder agrees to tender and sell
to Purchaser all of the Shares pursuant to the terms of the Offer. If requested
by Purchaser to so tender and sell the Shares, Shareholder agrees that
Shareholder shall deliver to the depository for the Offer for receipt prior to
the Expiration Date (as defined in the Offer) of the Offer, either a letter of
transmittal together with the certificates for the Shares, if available, or a
"Notice of Guaranteed Delivery", if the Shares are not available. Shareholder
agrees not to withdraw any Shares tendered into the Offer. Upon such tender
Shareholder will be relieved of any obligation under Sec. 1.1 hereof.

2. Representations and Warranties of Shareholder.


                                      -4-
<PAGE>

      Shareholder hereby represents and warrants to Purchaser as follows:

      2.1 Title.

            Shareholder is the owner (both beneficially as to Shares held other
than as Trustee and of record only as Trustee) of the Shares as set forth on
Schedule A. Except for the Shares Shareholder is not the record or beneficial
owner of, and does not have any other rights of any nature to acquire any
additional shares of, any shares of capital stock of the Company. Shareholder
will deliver, in accordance with the terms of this Agreement, all of the Shares,
free and clear of all security interests, liens, claims, pledges, options,
restrictions, rights of first refusal, agreements, limitations on Shareholder's
voting rights, charges and other encumbrances of any nature whatsoever, and,
except as provided in this Agreement, Shareholder has not appointed or granted
any proxy, which appointment or grant is still effective, with respect to any of
the Shares. The Shareholder has sole power of disposition with respect to all of
the Shares and sole voting power with respect to the matters set forth in
Section 6 hereof with respect to the Shares.

      2.2 Authority Relative to This Agreement.

            Shareholder has all necessary power and authority to execute and
deliver this Agreement, to perform Shareholder's obligations hereunder and to
consummate the transactions contemplated hereby. This Agreement has been duly
and validly executed and delivered by Shareholder and, assuming the due
authorization, execution and delivery by Purchaser, constitutes a legal, valid
and binding obligation of Shareholder enforceable against Shareholder in
accordance with its terms.

      2.3 No Conflict.

            The execution and delivery of this Agreement by Shareholder does
not, and the performance of this Agreement by Shareholder will not, (a) except
for any filings required under the HSR Act and for requirements of federal and
state securities laws, require any consent, approval, authorization or permit
of, or filing with or notification to, any governmental or regulatory authority,
domestic or foreign, or (b) conflict with, violate or result in any breach of or
constitute a default under (or an event which with notice or lapse of time or
both would become a default under) any agreement, judgment, injunction, order,
law, rule, regulation, decree or arrangement to which Shareholder is a party or
is bound.


                                      -5-
<PAGE>

      2.4 Brokers.

            Except for Salomon Smith Barney, whose fees will be paid by the
Company and a true and correct copy of whose engagement letter has been provided
by the Company, no broker, finder or investment banker is entitled to any
brokerage, finder's or other fee or commission in connection with the
transactions contemplated hereby based upon arrangements made by or on behalf of
Shareholder or the Company.

3. Representations and Warranties of Purchaser and Parent.

      3.1 Authority Relative to This Agreement.

            Purchaser and Parent have all necessary power and authority to
execute and deliver this Agreement, to perform its obligations hereunder and to
consummate the transactions contemplated hereby. The execution and delivery of
this Agreement by Purchaser and the consummation by Purchaser of the
transactions contemplated hereby have been duly and validly authorized by all
necessary corporate action on the part of Purchaser and Parent. This Agreement
has been duly and validly executed and delivered by Purchaser and Parent as
Guarantor, assuming the due authorization, execution and delivery by
Shareholder, constitutes a legal, valid and binding obligation of Purchaser and
Parent, enforceable against Purchaser and Parent in accordance with its terms.

      3.2 No Conflict.

            The execution and delivery of this Agreement by Purchaser and Parent
does not, and the performance of this Agreement by Purchaser and Parent will
not, (a) except for any filings required under the HSR Act and for requirements
of federal and state securities laws, require any consent, approval,
authorization or permit of, or filing with or notification to, any governmental
or regulatory authority, domestic or foreign, (b) conflict with or violate the
certificate of incorporation or bylaws of Purchaser or Parent, (c) conflict
with, violate or result in any breach of or constitute a default under (or an
event which with notice or lapse of time or both would become a default under)
any agreement, judgment, injunction, order, law, rule, regulation, decree or
arrangement applicable to Purchaser or Parent or by which any property or asset
of Purchaser or Parent is bound or affected, other than, in the case of clause
(c), any such conflicts, violations, breaches or defaults that, individually or
in the aggregate, would not materially impair the ability of Purchaser or Parent
to perform its obligations hereunder.

      3.3 Brokers.

            Except for Credit Suisse First Boston, whose fees will be paid by
Purchaser, no broker, finder or investment banker is entitled to any brokerage,
finder's or other fee or commission from Shareholder in connection with the
transactions contemplated hereby based upon arrangements made by or on behalf of
Purchaser.


                                      -6-
<PAGE>

      3.4 Investment Intent.

            Purchaser hereby represents that any securities it purchases
pursuant to this Agreement are being purchased for its own account for
investment and not with a view to, or for sale in connection with, any public
distribution thereof.

4. Covenant of Shareholder.

      No Solicitation of Transactions. Shareholder and his affiliates shall not,
and Shareholder and his affiliates shall use their best efforts to ensure that
Shareholder's representatives and agents (including, but not limited to,
investment bankers, attorneys and accountants) and his affiliates' officers,
directors, employees, representatives and agents do not, directly or indirectly,
encourage, solicit, participate in or initiate discussions or negotiations with,
or provide any information to, any corporation, partnership, person or other
entity or group (other than Purchaser or any of its affiliates or
representatives) concerning any proposal or offer to acquire all or a
substantial part of the business or properties of the Company or any of its
subsidiaries, whether by merger, tender offer, exchange offer, sale of assets or
similar transaction involving the Company or any subsidiary, division or
operating or principal business unit of the Company (an "Acquisition Proposal"),
except that the provisions of this Section 4 shall not restrict the
Shareholder's ability to act in such Shareholder's capacity as a director of the
Company in accordance with Section 6.8 of the Merger Agreement. Shareholder
shall immediately cease and cause to be terminated any existing activities,
discussions or negotiations by Shareholder or his affiliates or any investment
banker, attorney, accountant or other advisor or representative of Shareholder
or his affiliates with parties conducted heretofore with respect to any of the
foregoing.

5. Additional Covenants of Shareholder.

      5.1 No Disposition. Shareholder hereby covenants and agrees that, except
as contemplated by this Agreement and except pursuant to the Offer, Shareholder
shall not, and shall not offer or agree to, sell, transfer, tender, assign, or
otherwise dispose of, or create or permit to exist any option, restriction,
right of first refusal, agreement or limitation on Shareholder's voting rights
with respect to, the Shares now owned or any other shares that may hereafter be
acquired by Shareholder.

      5.2 Compliance of Shareholder with this Agreement. Shareholder shall take
all actions and forbear from all actions, in each case, necessary in order that
(a) all of Shareholder's representations and warranties hereunder are true and
correct and (b) Shareholder fulfills all of its obligations hereunder.


                                      -7-
<PAGE>

6. Voting Agreement; Proxy of Shareholder.

      6.1 Voting Agreement.

            Shareholder hereby agrees that, during the time this Agreement is in
effect, at any meeting of the stockholders of the Company, however called, and
in any action by written consent of the stockholders of the Company, Shareholder
shall, to the extent applicable, (a) vote (or execute a consent in respect of)
all of the Shares in favor of the Merger, the Merger Agreement (as amended from
time to time) and any of the transactions contemplated by the Merger Agreement;
(b) vote (or execute a consent in respect of) the Shares against any action or
agreement that would result in a breach of any covenant, representation or
warranty or any other obligation of the Company under the Merger Agreement; and
(c) vote (or execute a consent in respect of) the Shares against any action or
agreement that would reasonably be expected to impede, interfere with, delay or
attempt to discourage the Offer or the Merger, including, but not limited to:
(i) any extraordinary corporate transaction (other than the Merger), such as a
merger, reorganization, recapitalization or liquidation involving the Company or
any of its Subsidiaries (as defined in the Merger Agreement) or any proposal
made in opposition to or in competition with the Merger; (ii) a sale or transfer
of a material amount of assets of the Company or any of its Subsidiaries; (iii)
any change in the management or board of directors of the Company, except as
otherwise agreed to in writing by Purchaser or Purchaser; (iv) any material
change in the present capitalization or dividend policy of the Company; or (v)
any other material change in the corporate structure or business of the Company
or any of its Subsidiaries.

      6.2 Irrevocable Proxy.

            Shareholder agrees that, in the event Shareholder shall fail to
comply with the provisions of Section 6.1 hereof as determined by Purchaser in
its sole discretion, such failure shall result, without any further action by
Shareholder, in the irrevocable appointment of Purchaser as the attorney and
proxy of Shareholder, with full power of substitution, to vote, and otherwise
act (by written consent or otherwise) with respect to all of the Shares that
Shareholder is entitled to vote at any meeting of stockholders of the Company
(whether annual or special and whether or not an adjourned or postponed meeting)
or consent in lieu of any such meeting or otherwise, on the matters and in the
manner specified in Section 6.1. THIS PROXY AND POWER OF ATTORNEY IS IRREVOCABLE
AND COUPLED WITH AN INTEREST AND IS EXECUTED AND INTENDED TO BE IRREVOCABLE IN
ACCORDANCE WITH THE PROVISIONS OF SECTION 212(e) OF THE DELAWARE GENERAL
CORPORATION LAW ("DGCL"). Shareholder hereby revokes, effective upon the
execution and delivery of the Merger Agreement by the parties thereto, all other
proxies and powers of attorney with respect to the Shares that Shareholder may
have heretofore appointed or granted, and no subsequent proxy or power of
attorney (except in furtherance of Shareholder's obligations under Section 6.1
hereof) shall be given or written consent executed (and if given or executed,
shall not be effective) by Shareholder with respect thereto so long as this
Agreement remains in effect.


                                      -8-
<PAGE>

7. Termination.

      Other than the Stock Option which shall be governed Section by 1.4(a)
hereof, this Agreement shall terminate automatically in the event that the
Merger Agreement is terminated in accordance with the terms and conditions
thereof.

8. Miscellaneous.

      8.1 Expenses.

            All costs and expenses incurred in connection with the transactions
contemplated by this Agreement shall be paid by the party incurring such
expenses.

      8.2 Further Assurances.

            Shareholder and Purchaser shall execute and deliver all such further
documents and instruments and take all such further action as may be necessary
in order to consummate the transactions contemplated hereby.

      8.3 Specific Performance.

            The parties hereto agree that irreparable damage would occur in the
event any provision of this Agreement were not performed in accordance with the
terms hereof and that the parties shall be entitled to specific performance of
the terms hereof, in addition to any other remedy at law or in equity.

      8.4 Entire Agreement.

            This Agreement constitutes the entire agreement between Purchaser
and Shareholder with respect to the subject matter hereof and supersedes all
prior agreements and understandings, both written and oral, between Purchaser
and Shareholder with respect to the subject matter hereof.

      8.5 Assignment.

            This Agreement shall not be assigned by operation of law or
otherwise, except that Purchaser may assign all or any of its rights hereunder
except that such assignment shall not relieve Purchaser of its obligations
hereunder if such assignee does not perform such obligations.


                                      -9-
<PAGE>

      8.6 Parties in Interest.

            This Agreement shall be binding upon, inure solely to the benefit
of, and be enforceable by, the parties hereto and their successors and permitted
assigns. Nothing in this Agreement, express or implied, is intended to or shall
confer upon any other person any right, benefit or remedy of any nature
whatsoever under or by reason of this Agreement.

      8.7 Amendment; Waiver.

            This Agreement may not be amended except by an instrument in writing
signed by the parties hereto. Any party hereto may (a) extend the time for the
performance of any obligation or other act of any other party hereto, (b) waive
any inaccuracy in the representations and warranties contained herein or in any
document delivered pursuant hereto and (c) waive compliance with any agreement
or condition contained herein. Any such extension or waiver shall be valid if
set forth in an instrument in writing signed by the party or parties to be bound
thereby.

      8.8 Severability.

            If any term or other provision of this Agreement is invalid, illegal
or incapable of being enforced by any rule of law, or public policy, all other
conditions and provisions of this Agreement shall nevertheless remain in full
force and effect so long as the economic or legal substance of this Agreement is
not affected in any manner materially adverse to any party. Upon such
determination that any term or other provision is invalid, illegal or incapable
of being enforced, the parties hereto shall negotiate in good faith to modify
this Agreement so as to effect the original intent of the parties as closely as
possible in a mutually acceptable manner in order that the terms of this
Agreement remain as originally contemplated to the fullest extent possible.

      8.9 Notices.

            All notices, requests, claims, demands and other communications
hereunder shall be in writing and shall be deemed to have been duly given when
delivered in person, by overnight courier or facsimile to the respective parties
as follows:

                  If to Purchaser:

                        PBC Acquisition Corp.
                        c/o Kluwer Academic Publishers bv
                        Spuilboulevard 50, 311GR Dordrecht
                        3300 AZ Dordrecht
                        Attention: Jeffrey K. Smith
                      
                        Fax #: (011)(31)(78) 639-2268


                                      -10-
<PAGE>

                  with a copy to:

                        Wolters Kluwer U.S. Corporation
                        161 North Clark Street
                        48th Floor
                        Chicago, Illinois 60601-3221
                        Attention: Bruce C. Lenz
                      
                        Fax #:  (312) 425-0233
                     
                  and to:

                        Pryor Cashman Sherman & Flynn LLP
                        410 Park Avenue
                        New York, New York 10022
                        Attention:  Arnold J. Schaab, Esq.

                        Fax #:  (212) 326-0806

                  if to Shareholder:

                        Mark and Hally Shaw
                        6884 Queenferry Circle
                        Boca Raton, Florida 33469

                        Fax #:  (561) 487-4137

                  with a copy to:

                        BRESSLER, AMERY & ROSS, P.C.
                        17 State Street
                        New York, New York 10004
                        Attention: Bernard Bressler, Esq.

                        Fax #:  (212) 425-9337

      8.10  Governing Law.

            This Agreement shall be governed by, and construed in accordance
with, the laws of the State of Delaware applicable to contracts executed in and
to be performed in Delaware without regard to any principles of choice of law or
conflicts of law of such State. All actions and proceedings arising out of or
relating to this Agreement shall be heard and determined in any state or federal
court sitting in Delaware. Each of the parties hereto (i) consents to submit
such 


                                      -11-
<PAGE>

party to the personal jurisdiction of any Federal court located in the
State of Delaware or any Delaware state court in the event any dispute arises
out of this Agreement or any of the transactions contemplated hereby, (ii)
agrees that such party will not attempt to deny or defeat such personal
jurisdiction by motion or other request for leave from any such court, (iii)
agrees that such party will not bring any action relating to this Agreement or
the transactions contemplated hereby in any court other than a Federal court
sitting in the state of Delaware or a Delaware state court and (iv) waives any
right to trial by jury with respect to any claim or proceeding related to or
arising out of this Agreement or any of the transactions contemplated hereby.

      8.11 Headings.

            The descriptive headings contained in this Agreement are included
for convenience of reference only and shall not affect in any way the meaning or
interpretation of this Agreement.

      8.12 Counterparts.

            This Agreement may be executed and delivered (including by facsimile
transmission) in one or more counterparts, and by the different parties hereto
in separate counterparts, each of which when as executed and delivered shall be
deemed to be an original but all of which taken together shall constitute one
and the same agreement.


                                      -12-
<PAGE>

      IN WITNESS WHEREOF, each of the parties hereto has caused this Agreement
to be duly executed and delivered as of the date first written above.

                                        PPC ACQUISITION CORP.


                                        By: /s/ Jeffrey K. Smith
                                           ----------------------------
                                           Name:  Jeffrey K. Smith
                                           Title: President
                             
                                        Shareholder
                             
                                          /s/ Mark Shaw
                                        -------------------------------
                                        Mark Shaw
                             
                                          /s/ Hally Shaw 
                                        -------------------------------
                                        Hally Shaw
                             
                                          /s/ Mark Shaw
                                        -------------------------------
                                        Mark Shaw, Trustee
                                        u/a Dtd. 8/25/76 FBO Jared Roger
                                        Shaw and Scott Harlen Shaw


                                      -13-
<PAGE>

      Kluwer Boston, Inc. in consideration of the undertakings hereunder by
Shareholders does hereby guaranty performance of the obligations undertake
herein by Purchaser and to the extent that such guarantee shall relate to the
payment of moneys, such guaranty shall be a guaranty of performance and not a
guaranty of collection.

                                        KLUWER BOSTON, INC.

                                        By:  /s/ Jeffrey K. Smith
                                           ----------------------------
                                           Name:  Jeffrey K. Smith
                                           Title: President


                                      -14-
<PAGE>

                                   SCHEDULE A

                               MARK AND HALLY SHAW

      Mark Shaw In Trust For Adult Children                             50,625

      Shares Owned Of Record and Beneficially
      By Mark Shaw Individually                                         16,460

      Shares Owned Of Record and Beneficially
      Jointly By Mark and Hally Shaw                                    13,582
                                                                        ------

                                                                        80,667


<PAGE>

                                                           


                            STOCK PURCHASE AGREEMENT

      Stock Purchase Agreement (this "Agreement"), dated as of June 10, 1998,
between PPC Acquisition Corp. ("Purchaser") and Ghanshyam Patel and Anila Patel
(together called "Shareholder").

      WHEREAS, Shareholder owns (beneficially) 10,554 shares of common stock,
par value $.10 per share ("Common Stock") of Plenum Publishing Corp. (the
"Company")(including shares as to which Shareholder has voting power pursuant to
the terms of the Company Qualified Profit Sharing Plan) all as set forth on
Schedule A hereto (the "Shares").

      WHEREAS, concurrently herewith, Kluwer Boston Inc. ("Parent") and
Purchaser, a wholly owned subsidiary of Parent are entering into an agreement
and plan of merger with the Company, dated as of June 10, 1998 (the "Merger
Agreement"), pursuant to which Purchaser has agreed to make a cash tender offer
(the "Offer") for, among other things, all outstanding shares of Common Stock of
the Company at $73.50 per share (or any higher price paid in the Offer, the
"Offer Price"), net to the seller in cash, to be followed by a merger of
Purchaser with and into the Company (the "Merger"); and

      WHEREAS, as a condition to the willingness of Purchaser and Parent to
enter into the Merger Agreement, Purchaser, whose performance hereunder is
guaranteed by Parent, has required that Shareholder agree, and in order to
induce Purchaser and Parent to enter into the Merger Agreement, Shareholder has
agreed, among other things, (i) to sell the Shares; (ii) to tender the Shares
into the Offer; (iii) to appoint Purchaser as Shareholder's proxy to vote the
Shares under certain circumstances, and (iv) with respect to certain questions
put to stockholders of the Company for a vote, to vote the Shares, in each case,
in accordance with the terms and conditions of this Agreement.

      NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained herein and other good and valuable consideration, the adequacy of
which is hereby acknowledged, and intending to be legally bound hereby, the
parties hereto agree as follows:

1. Purchase and Sale of Shares.

      1.1 Tender of Shares; Purchase of Shares.

            (a) Shareholder agrees to tender and sell to Purchaser all of the
Shares pursuant to the terms of the Offer. Shareholder agrees that Shareholder
shall deliver to the depository for the Offer for receipt prior to the
Expiration Date (as defined in the Offer) of the Offer, either a letter of
transmittal together with the certificates for the Shares, if available, or a
"Notice of Guaranteed Delivery", if the Shares are not available. Unless an
election is made by Purchaser under Section 1.1(b), Shareholder agrees not to
withdraw any Shares tendered into the Offer. Upon such tender Shareholder will
be relieved of any obligation under Sec. 1.1(b) hereof.

            (b) Upon the election of Purchaser on the terms and subject to the
conditions 
<PAGE>

set forth in this Agreement, on (and assuming the occurrence of) the Closing
Date (as defined herein), Purchaser will purchase from the Shareholder, and the
Shareholder will sell and transfer to the Purchaser, all of the Shares, free and
clear of all mortgages, pledges, security interest, encumbrances, liens,
options, debts, charges, claims and restrictions of any kind, at a purchase
price per share equal to the Offer Price.

      1.2 Conditions to the Closing.

            Subject to the provisions of the first sentence of Section 1.3
hereof, the obligations of the parties to consummate the transactions
contemplated by Section 1.1(b) hereof are subject to the following conditions:
(a) any waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of
1976, as amended (the "HSR Act") applicable to the delivery of the Shares and
the consummation of the Offer shall have expired or been terminated; and (b)
there shall be no preliminary or permanent injunction or other order by any
court of competent jurisdiction restricting, preventing or prohibiting the
delivery of the Shares. Purchaser and Shareholder shall each promptly after the
date hereof make such filings and provide such information as may be required
under the HSR Act with respect to the sale of the Shares.

      1.3 Closing.

            Subject to the conditions contained in this Agreement and subject to
Sections 1.4 through 1.8, the closing of the transactions contemplated by
Section 1.1(b) hereof (the "Closing") shall occur at a site designated by
Purchaser simultaneously with the acceptance by Purchaser of the shares of
Common Stock validly tendered and not withdrawn pursuant to the terms of the
Offer in accordance with the terms and conditions of the Offer and the Merger
Agreement (the "Closing Date"). At the Closing and subject to the conditions
contained in this Agreement, Purchaser hereby directs Shareholder to deliver to
Purchaser a certificate or certificates evidencing the Shares, each such
certificate being duly endorsed in blank and accompanied by such stock powers
and such other documents as may be necessary in Purchaser's judgment to transfer
record ownership of the Shares into Purchaser's name on the stock transfer books
of the Company, and Purchaser will purchase the Shares at a purchase price equal
to the Offer Price. All payments made by Purchaser to Shareholder pursuant to
this Section 1.3 shall be made by wire transfer of immediately available funds
to an account designated by Shareholder, or by certified bank check payable to
Shareholder, in an amount equal to the sum of the product of (i) the Offer Price
and (ii) the total number of Shares delivered at the Closing.

      1.4 Stock Option.

            Effective upon expiration or termination of the Offer for the
reasons set forth in Section 1.5 below, Purchaser shall have an irrevocable
option (the "Stock Option") exercisable on the terms and conditions set forth in
Section 1.5 below to purchase the Shares, at a purchase price equal to the Offer
Price.


                                      -2-
<PAGE>

      1.5 Termination or Expiration of Offer and Exercise of Stock Option.

            (a)(i) If the Offer is terminated by Purchaser for the reasons set
forth in paragraph (d) of Annex I to the Merger Agreement or (ii) in the case of
the expiration of the Offer, if the Offer expires without the purchase of Shares
thereunder and either without satisfaction of the Minimum Condition (as defined
in the Merger Agreement) or after the occurrence of circumstances giving rise to
a right of termination by Purchaser for the reasons set forth in paragraph (d)
of Annex I to the Merger Agreement, in each case without any violation of the
Offer or the Merger Agreement by Purchaser or Parent, then the Stock Option may
be exercised by Purchaser, in whole and for all of Shareholder's Shares but not
in part or for less than all of Shareholder's Shares. Notice of exercise may be
given at any time during the period (the "Exercise Period") commencing on the
date on which the Offer is terminated or expires (under the circumstances
provided in this Section 1.5) and ending on March 31, 1999, whichever is later.
In addition, Purchaser may also exercise the Stock Option if the Merger
Agreement shall terminate by reason of the Company's exercise of its termination
rights pursuant to Section 8.1(c)(ii) of the Merger Agreement, whereupon the
Exercise Period shall commence on the date such termination rights are exercised
and end on March 31, 1999, whichever is later.

            (b) In the event Purchaser wishes to exercise the Stock Option,
Purchaser shall send a written notice (an "Exercise Notice") during the Exercise
Period to the Shareholder specifying that Purchaser shall purchase the Shares
held by Shareholder and a date, which shall be a business day, and a place,
which shall be in the city of New York, for the closing of such purchase (the
"Stock Option Closing").

            (c) Upon receipt of the Exercise Notice, Shareholder shall be
obligated to deliver to Purchaser a certificate or certificates representing the
Shares held by Shareholder (or to direct the depositary for the Offer to so
deliver such certificates or certificates), in accordance with the terms of this
Agreement, on the later of the date specified in such Exercise Notice or the
first business day on which the conditions specified in Section 1.6 shall be
satisfied. The date specified in such Exercise Notice may be as early as one
business day after the date of such Exercise Notice but shall not be later than
five (5) business days after the later of (i) the date of such Exercise Notice,
or (ii) the date all conditions under Section 1.6 are satisfied.

      1.6 Conditions to Delivery of the Shares.

            The obligation of the Shareholder to deliver, and of the Purchaser
to pay for, the Shares upon exercise of the Stock Option is subject to the
following conditions:

            (a) All waiting periods under the Hart-Scott-Rodino Antitrust
Improvements Act of 1976, as amended, applicable to the exercise of the Stock
Option and the delivery of the Shares shall have expired or been terminated; and

            (b) There shall be no permanent injunction or other order by any
court of 


                                      -3-
<PAGE>

competent jurisdiction restricting, preventing or prohibiting the exercise of
the Stock Option or the delivery of the Shares in respect of such exercise.

      1.7 Stock Option Closing.

            At the Stock Option Closing, the Shareholder will deliver to
Purchaser a certificate or certificates evidencing the Shares owned by
Shareholder, each such certificate being duly endorsed in blank and accompanied
by such stock powers and such other documents as may be necessary in Purchaser's
judgment to transfer record ownership of the Shares into Purchaser's name on the
stock transfer books of the Company, and Purchaser will purchase the delivered
Shares at the Offer Price. All payments made by Purchaser to Shareholder
pursuant to this Section 1.7 shall be made by wire transfer of immediately
available funds or by certified bank check payable to Shareholder, in an amount
equal to the product of (a) the Offer Price and (b) the Shares delivered by
Shareholder in respect of the Stock Option Closing.

      1.8 Adjustments Upon Changes in Capitalization.

            In the event of any change in the number of issued and outstanding
shares of Common Stock by reason of any stock dividend, subdivision, merger,
recapitalization, combination, conversion or exchange of shares, or any other
change in the corporate or capital structure of the Company (including, without
limitation, the declaration of payment of an extraordinary dividend of cash or
securities) which would have the effect of diluting or otherwise adversely
affecting Purchaser's rights and privileges under this Agreement, the number and
kind of the shares and the consideration payable in respect to the Shares shall
be appropriately and equitably adjusted to restore to Purchaser its rights and
privileges under this Agreement. Without limiting the scope of the foregoing, in
any such event, at the option of Purchaser, the Stock Option shall represent the
right to purchase, in addition to the number and kind of Shares which Purchaser
would be entitled to purchase pursuant to the immediately preceding sentence,
whatever securities, cash or other property the Shares subject to the Stock
Option shall have been converted into or otherwise exchanged for, together with
any securities, cash or other property which shall have been distributed with
respect to such Shares.


                                      -4-
<PAGE>

2. Representations and Warranties of Shareholder.

      Shareholder hereby represents and warrants to Purchaser as follows:

      2.1 Title.

            Shareholder is the owner (both beneficially and of record, or
beneficially as respects the interest of Shareholder in shares held in the
Profit Sharing Plan) of the Shares set forth on Schedule A. Except for the
Shares and except for the interest of Shareholder in shares held for his account
in the Profit Sharing Plan, Shareholder is not the record or beneficial owner
of, and does not have any other rights of any nature to acquire any additional
shares of, any shares of capital stock of the Company. Shareholder will deliver,
in accordance with the terms of this Agreement, all of the Shares, free and
clear of all security interests, liens, claims, pledges, options, restrictions,
rights of first refusal, agreements, limitations on Shareholder's voting rights,
charges and other encumbrances of any nature whatsoever, and, except as provided
in this Agreement, Shareholder has not appointed or granted any proxy, which
appointment or grant is still effective, with respect to any of the Shares. The
Shareholder has sole power of disposition with respect to all of the Shares and
sole voting power with respect to the matters set forth in Section 6 hereof with
respect to the Shares.

      2.2 Authority Relative to This Agreement.

            Shareholder has all necessary power and authority to execute and
deliver this Agreement, to perform Shareholder's obligations hereunder and to
consummate the transactions contemplated hereby. This Agreement has been duly
and validly executed and delivered by Shareholder and, assuming the due
authorization, execution and delivery by Purchaser, constitutes a legal, valid
and binding obligation of Shareholder enforceable against Shareholder in
accordance with its terms.

      2.3 No Conflict.

            The execution and delivery of this Agreement by Shareholder does
not, and the performance of this Agreement by Shareholder will not, (a) except
for any filings required under the HSR Act and for requirements of federal and
state securities laws, require any consent, approval, authorization or permit
of, or filing with or notification to, any governmental or regulatory authority,
domestic or foreign, or (b) conflict with, violate or result in any breach of or
constitute a default under (or an event which with notice or lapse of time or
both would become a default under) any agreement, judgment, injunction, order,
law, rule, regulation, decree or arrangement to which Shareholder is a party or
is bound.


                                      -5-
<PAGE>

      2.4 Brokers.

            Except for Salomon Smith Barney, whose fees will be paid by the
Company and a true and correct copy of whose engagement letter has been provided
by the Company, no broker, finder or investment banker is entitled to any
brokerage, finder's or other fee or commission in connection with the
transactions contemplated hereby based upon arrangements made by or on behalf of
Shareholder.

3. Representations and Warranties of Purchaser and Parent.

      3.1 Authority Relative to This Agreement.

            Purchaser and Parent have all necessary power and authority to
execute and deliver this Agreement, to perform its obligations hereunder and to
consummate the transactions contemplated hereby. The execution and delivery of
this Agreement by Purchaser and the consummation by Purchaser of the
transactions contemplated hereby have been duly and validly authorized by all
necessary corporate action on the part of Purchaser and Parent. This Agreement
has been duly and validly executed and delivered by Purchaser and Parent as
Guarantor, assuming the due authorization, execution and delivery by
Shareholder, constitutes a legal, valid and binding obligation of Purchaser,
enforceable against Purchaser in accordance with its terms.

      3.2 No Conflict.

            The execution and delivery of this Agreement by Purchaser does not,
and the performance of this Agreement by Purchaser and Parent will not, (a)
except for any filings required under the HSR Act and for requirements of
federal and state securities laws, require any consent, approval, authorization
or permit of, or filing with or notification to, any governmental or regulatory
authority, domestic or foreign, (b) conflict with or violate the certificate of
incorporation or bylaws of Purchaser or Parent, (c) conflict with, violate or
result in any breach of or constitute a default under (or an event which with
notice or lapse of time or both would become a default under) any agreement,
judgment, injunction, order, law, rule, regulation, decree or arrangement
applicable to Purchaser or Parent or by which any property or asset of Purchaser
or Parent is bound or affected, other than, in the case of clause (c), any such
conflicts, violations, breaches or defaults that, individually or in the
aggregate, would not materially impair the ability of Purchaser or Parent to
perform its obligations hereunder.

      3.3 Brokers.

            Except for Credit Suisse First Boston, whose fees will be paid by
Purchaser, no broker, finder or investment banker is entitled to any brokerage,
finder's or other fee or commission from Shareholder in connection with the
transactions contemplated hereby based upon arrangements made by or on behalf of
Purchaser.


                                      -6-
<PAGE>

      3.4 Investment Intent.

            Purchaser hereby represents that any securities it purchases
pursuant to this Agreement are being purchased for its own account for
investment and not with a view to, or for sale in connection with, any public
distribution thereof.

4. Covenant of Shareholder.

      No Solicitation of Transactions. Shareholder and his affiliates shall not,
and Shareholder and his affiliates shall use their best efforts to ensure that
Shareholder's representatives and agents (including, but not limited to,
investment bankers, attorneys and accountants) and his affiliates' officers,
directors, employees, representatives and agents do not, directly or indirectly,
encourage, solicit, participate in or initiate discussions or negotiations with,
or provide any information to, any corporation, partnership, person or other
entity or group (other than Purchaser or any of its affiliates or
representatives) concerning any proposal or offer to acquire all or a
substantial part of the business or properties of the Company or any of its
subsidiaries, whether by merger, tender offer, exchange offer, sale of assets or
similar transaction involving the Company or any subsidiary, division or
operating or principal business unit of the Company (an "Acquisition Proposal").
Shareholder shall immediately cease and cause to be terminated any existing
activities, discussions or negotiations by Shareholder or his affiliates or any
investment banker, attorney, accountant or other advisor or representative of
Shareholder or his affiliates with parties conducted heretofore with respect to
any of the foregoing.

5. Additional Covenants of Shareholder.

      5.1 No Disposition. Shareholder hereby covenants and agrees that, except
as contemplated by this Agreement and except pursuant to the Offer, Shareholder
shall not, and shall not offer or agree to, sell, transfer, tender, assign, or
otherwise dispose of, or create or permit to exist any option, restriction,
right of first refusal, agreement or limitation on Shareholder's voting rights,
with respect to, the Shares now owned or any other shares that may hereafter be
acquired by Shareholder.

      5.2 Compliance of Shareholder with this Agreement. Shareholder shall take
all actions and forbear from all actions, in each case, necessary in order that
(a) all of Shareholder's representations and warranties hereunder are true and
correct and (b) Shareholder fulfills all of its obligations hereunder.


                                      -7-
<PAGE>

6. Voting Agreement; Proxy of Shareholder.

      6.1 Voting Agreement.

            Shareholder hereby agrees that, during the time this Agreement is in
effect, at any meeting of the stockholders of the Company, however called, and
in any action by written consent of the stockholders of the Company, Shareholder
shall, to the extent applicable, (a) vote (or execute a consent in respect of)
all of the Shares in favor of the Merger, the Merger Agreement (as amended from
time to time) and any of the transactions contemplated by the Merger Agreement;
(b) vote (or execute a consent in respect of) the Shares against any action or
agreement that would result in a breach of any covenant, representation or
warranty or any other obligation of the Company under the Merger Agreement; and
(c) vote (or execute a consent in respect of) the Shares against any action or
agreement that would reasonably be expected to impede, interfere with, delay or
attempt to discourage the Offer or the Merger, including, but not limited to:
(i) any extraordinary corporate transaction (other than the Merger), such as a
merger, reorganization, recapitalization or liquidation involving the Company or
any of its Subsidiaries (as defined in the Merger Agreement) or any proposal
made in opposition to or in competition with the Merger; (ii) a sale or transfer
of a material amount of assets of the Company or any of its Subsidiaries; (iii)
any change in the management or board of directors of the Company, except as
otherwise agreed to in writing by Purchaser or Purchaser; (iv) any material
change in the present capitalization or dividend policy of the Company; or (v)
any other material change in the corporate structure or business of the Company
or any of its Subsidiaries.

      6.2 Irrevocable Proxy.

            Shareholder agrees that, in the event Shareholder shall fail to
comply with the provisions of Section 6.1 hereof as determined by Purchaser in
its sole discretion, such failure shall result, without any further action by
Shareholder, in the irrevocable appointment of Purchaser as the attorney and
proxy of Shareholder, with full power of substitution, to vote, and otherwise
act (by written consent or otherwise) with respect to all of the Shares that
Shareholder is entitled to vote at any meeting of stockholders of the Company
(whether annual or special and whether or not an adjourned or postponed meeting)
or consent in lieu of any such meeting or otherwise, on the matters and in the
manner specified in Section 6.1. THIS PROXY AND POWER OF ATTORNEY IS IRREVOCABLE
AND COUPLED WITH AN INTEREST AND IS EXECUTED AND INTENDED TO BE IRREVOCABLE IN
ACCORDANCE WITH THE PROVISIONS OF SECTION 212(e) OF THE DELAWARE GENERAL
CORPORATION LAW ("DGCL"). Shareholder hereby revokes, effective upon the
execution and delivery of the Merger Agreement by the parties thereto, all other
proxies and powers of attorney with respect to the Shares that Shareholder may
have heretofore appointed or granted, and no subsequent proxy or power of
attorney (except in furtherance of Shareholder's obligations under Section 6.1
hereof) shall be given or written consent executed (and if given or executed,
shall not be effective) by Shareholder with respect thereto so long as this
Agreement remains in effect.


                                      -8-
<PAGE>

7. Termination.

      Other than the Stock Option which shall be governed by Section 1.4(a)
hereof, this Agreement shall terminate automatically in the event that the
Merger Agreement is terminated in accordance with the terms and conditions
thereof.

8. Miscellaneous.

      8.1 Expenses.

            All costs and expenses incurred in connection with the transactions
contemplated by this Agreement shall be paid by the party incurring such
expenses.

      8.2 Further Assurances.

            Shareholder and Purchaser shall execute and deliver all such further
documents and instruments and take all such further action as may be necessary
in order to consummate the transactions contemplated hereby.

      8.3 Specific Performance.

            The parties hereto agree that irreparable damage would occur in the
event any provision of this Agreement were not performed in accordance with the
terms hereof and that the parties shall be entitled to specific performance of
the terms hereof, in addition to any other remedy at law or in equity.

      8.4 Entire Agreement.

            This Agreement constitutes the entire agreement between Purchaser
and Shareholder with respect to the subject matter hereof and supersedes all
prior agreements and understandings, both written and oral, between Purchaser
and Shareholder with respect to the subject matter hereof.

      8.5 Assignment.

            This Agreement shall not be assigned by operation of law or
otherwise, except that Purchaser may assign all or any of its rights hereunder
except that such assignment shall not relieve Purchaser of its obligations
hereunder if such assignee does not perform such obligations.


                                      -9-
<PAGE>

      8.6 Parties in Interest.

            This Agreement shall be binding upon, inure solely to the benefit
of, and be enforceable by, the parties hereto and their successors and permitted
assigns. Nothing in this Agreement, express or implied, is intended to or shall
confer upon any other person any right, benefit or remedy of any nature
whatsoever under or by reason of this Agreement.

      8.7 Amendment; Waiver.

            This Agreement may not be amended except by an instrument in writing
signed by the parties hereto. Any party hereto may (a) extend the time for the
performance of any obligation or other act of any other party hereto, (b) waive
any inaccuracy in the representations and warranties contained herein or in any
document delivered pursuant hereto and (c) waive compliance with any agreement
or condition contained herein. Any such extension or waiver shall be valid if
set forth in an instrument in writing signed by the party or parties to be bound
thereby.

      8.8 Severability.

            If any term or other provision of this Agreement is invalid, illegal
or incapable of being enforced by any rule of law, or public policy, all other
conditions and provisions of this Agreement shall nevertheless remain in full
force and effect so long as the economic or legal substance of this Agreement is
not affected in any manner materially adverse to any party. Upon such
determination that any term or other provision is invalid, illegal or incapable
of being enforced, the parties hereto shall negotiate in good faith to modify
this Agreement so as to effect the original intent of the parties as closely as
possible in a mutually acceptable manner in order that the terms of this
Agreement remain as originally contemplated to the fullest extent possible.

      8.9 Notices.

            All notices, requests, claims, demands and other communications
hereunder shall be in writing and shall be deemed to have been duly given when
delivered in person, by overnight courier or facsimile to the respective parties
as follows:

                  If to Purchaser:

                        PPC Acquisition Corp.
                        c/o Kluwer Academic Publishers bv
                        Spuilboulevard 50, 311GR Dordrecht
                        3300 AZ Dordrecht, The Netherlands
                        Attention: Jeffrey K. Smith

                        Fax #: (011)(31)(78) 639-2268


                                      -10-
<PAGE>

                  with a copy to:

                        Wolters Kluwer U.S. Corporation
                        161 North Clark Street
                        48th Floor
                        Chicago, Illinois 60601-3221
                        Attention: Bruce C. Lenz

                        Fax #:  (312) 425-0233

                  and to:

                        Pryor Cashman Sherman & Flynn LLP
                        410 Park Avenue
                        New York, New York 10022
                        Attention: Arnold J. Schaab, Esq.

                        Fax #:  (212) 326-0806

                  if to Shareholder:

                        Ghanshyam and Anila Patel
                        9 Jeffrey Court
                        Syosset, New York 11791

                        Fax #:  (516) 921-3263

                  with a copy to:

                        BRESSLER, AMERY & ROSS, P.C.
                        17 State Street
                        New York, New York 10004
                        Attention: Bernard Bressler, Esq.

                        Fax #:  (212) 425-9337

      8.10 Governing Law.

            This Agreement shall be governed by, and construed in accordance
with, the laws of the State of Delaware applicable to contracts executed in and
to be performed in Delaware without regard to any principles of choice of law or
conflicts of law of such State. All actions and proceedings arising out of or
relating to this Agreement shall be heard and determined in any 


                                      -11-
<PAGE>

state or federal court sitting in Delaware. Each of the parties hereto (i)
consents to submit such party to the personal jurisdiction of any Federal court
located in the State of Delaware or any Delaware state court in the event any
dispute arises out of this Agreement or any of the transactions contemplated
hereby, (ii) agrees that such party will not attempt to deny or defeat such
personal jurisdiction by motion or other request for leave from any such court,
(iii) agrees that such party will not bring any action relating to this
Agreement or the transactions contemplated hereby in any court other than a
Federal court sitting in the state of Delaware or a Delaware state court and
(iv) waives any right to trial by jury with respect to any claim or proceeding
related to or arising out of this Agreement or any of the transactions
contemplated hereby.

      8.11 Headings.

            The descriptive headings contained in this Agreement are included
for convenience of reference only and shall not affect in any way the meaning or
interpretation of this Agreement.

      8.12 Counterparts.

            This Agreement may be executed and delivered (including by facsimile
transmission) in one or more counterparts, and by the different parties hereto
in separate counterparts, each of which when as executed and delivered shall be
deemed to be an original but all of which taken together shall constitute one
and the same agreement.


                                      -12-
<PAGE>

      IN WITNESS WHEREOF, each of the parties hereto has caused this Agreement
to be duly executed and delivered as of the date first written above.

                                    PPC ACQUISITION CORP.


                                    By:  /s/ Jeffrey K. Smith
                                       ----------------------------
                                       Name:  Jeffrey K. Smith
                                       Title: President

                                    Shareholder

                                     /s/ Ghanshyam Patel
                                    -------------------------------
                                    Ghanshyam Patel

                                     /s/ Anila Patel
                                    -------------------------------
                                    Anila Patel


                                      -13-
<PAGE>

      Kluwer Boston, Inc. in consideration of the undertakings hereunder by
Shareholder does hereby guaranty performance of the obligations undertake herein
by Purchaser and to the extent that such guarantee shall relate to the payment
of moneys, such guaranty shall be a guaranty of performance and not a guaranty
of collection.

                                    KLUWER BOSTON, INC.


                                    By: /s/ Jeffrey K. Smith
                                       ----------------------------
                                       Name:  Jeffrey K. Smith:
                                       Title: President


                                      -14-
<PAGE>

                                   SCHEDULE A

                            GHANSHYAM AND ANILA PATEL

            Shares Owned In Account Designated
            For Ghanshyam Patel In Plenum Publishing
            Profit Sharing Plan                                          5,204

            Shares Owned Jointly By Ghanshyam and
            Anila Patel                                                  5,350
                                                                         -----

                                                                        10,554


<PAGE>

                                                          


                            STOCK PURCHASE AGREEMENT

      Stock Purchase Agreement (this "Agreement"), dated as of June 10, 1998,
between PPC Acquisition Corp. ("Purchaser") and Bernard Bressler
("Shareholder").

      WHEREAS, Shareholder owns (both beneficially and of record) 11,757
shares(1) of common stock, par value $.10 per share ("Common Stock") of Plenum
Publishing Corp. (the "Company")(including shares as to which Shareholder has
power pursuant to the terms of a self directed IRA Plan)(the "Shares").

      WHEREAS, concurrently herewith, Kluwer Boston Inc. ("Parent") and
Purchaser, a wholly owned subsidiary of Parent, are entering into an agreement
and plan of merger with the Company, dated as of June 10, 1998 (the "Merger
Agreement"), pursuant to which Purchaser has agreed to make a cash tender offer
(the "Offer") for, among other things, all outstanding shares of Common Stock of
the Company at $73.50 per share (or any higher price paid in the Offer, the
"Offer Price"), net to the seller in cash, to be followed by a merger of
Purchaser with and into the Company (the "Merger"); and

      WHEREAS, as a condition to the willingness of Purchaser and Parent to
enter into the Merger Agreement, Purchaser, whose performance hereunder is
guaranteed by Parent, has required that Shareholder agree, and in order to
induce Purchaser and Parent to enter into the Merger Agreement, Shareholder has
agreed, among other things, (i) to sell the Shares; (ii) to tender the Shares
into the Offer; (iii) to appoint Purchaser as Shareholder's proxy to vote the
Shares under certain circumstances, and (iv) with respect to certain questions
put to stockholders of the Company for a vote, to vote the Shares, in each case,
in accordance with the terms and conditions of this Agreement.

      NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained herein and other good and valuable consideration, the adequacy of
which is hereby acknowledged, and intending to be legally bound hereby, the
parties hereto agree as follows:

1. Purchase and Sale of Shares.

      1.1 Tender of Shares; Purchase of Shares.

            (a) Shareholder agrees to tender and sell to Purchaser all of the
Shares pursuant to the terms of the Offer. Shareholder agrees that Shareholder
shall deliver to the depository for the Offer for receipt prior to the
Expiration Date (as defined in the Offer) of the Offer, either a letter of
transmittal together with the certificates for the Shares, if available, or a
"Notice of Guaranteed Delivery", if the Shares are not available. Unless an
election is made by Purchaser under Section 1.1(b), Shareholder agrees not to
withdraw any Shares tendered into the

- ------------
      (1) Shareholder anticipates contributing 1000 shares to charities before
June 30, 1998 and such shares are not subject to this Agreement and are not
included in the total set forth. To the extent not contributed they will
constitute additional shares subject to this Agreement.
<PAGE>

Offer. Upon such tender Shareholder will be relieved of any obligation under
Sec. 1.1(b) hereof.

            (b) Upon the election of Purchaser on the terms and subject to the
conditions set forth in this Agreement, on (and assuming the occurrence of) the
Closing Date (as defined herein), Purchaser will purchase from the Shareholder,
and the Shareholder will sell and transfer to the Purchaser, all of the Shares,
free and clear of all mortgages, pledges, security interest, encumbrances,
liens, options, debts, charges, claims and restrictions of any kind, at a
purchase price per share equal to the Offer Price.

      1.2 Conditions to the Closing.

            Subject to the provisions of the first sentence of Section 1.3
hereof, the obligations of the parties to consummate the transactions
contemplated by Section 1.1(b) hereof are subject to the following conditions:
(a) any waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of
1976, as amended (the "HSR Act") applicable to the delivery of the Shares and
the consummation of the Offer shall have expired or been terminated; and (b)
there shall be no preliminary or permanent injunction or other order by any
court of competent jurisdiction restricting, preventing or prohibiting the
delivery of the Shares. Purchaser and Shareholder shall each promptly after the
date hereof make such filings and provide such information as may be required
under the HSR Act with respect to the sale of the Shares.

      1.3 Closing.

            Subject to the conditions contained in this Agreement and subject to
Sections 1.4 through 1.8, the closing of the transactions contemplated by
Section 1.1(b) hereof (the "Closing") shall occur at a site designated by
Purchaser simultaneously with the acceptance by Purchaser of the shares of
Common Stock validly tendered and not withdrawn pursuant to the terms of the
Offer in accordance with the terms and conditions of the Offer and the Merger
Agreement (the "Closing Date"). At the Closing and subject to the conditions
contained in this Agreement, Purchaser hereby directs Shareholder to deliver to
Purchaser a certificate or certificates evidencing the Shares, each such
certificate being duly endorsed in blank and accompanied by such stock powers
and such other documents as may be necessary in Purchaser's judgment to transfer
record ownership of the Shares into Purchaser's name on the stock transfer books
of the Company, and Purchaser will purchase the Shares at a purchase price equal
to the Offer Price. All payments made by Purchaser to Shareholder pursuant to
this Section 1.3 shall be made by wire transfer of immediately available funds
to an account designated by Shareholder, or by certified bank check payable to
Shareholder, in an amount equal to the sum of the product of (i) the Offer Price
and (ii) the total number of Shares delivered at the Closing.


                                      -2-
<PAGE>

      1.4 Stock Option.

            Effective upon expiration or termination of the Offer for the
reasons set forth in Section 1.5 below, Purchaser shall have an irrevocable
option (the "Stock Option") exercisable on the terms and conditions set forth in
Section 1.5 below to purchase the Shares, at a purchase price equal to the Offer
Price.

      1.5 Termination or Expiration of Offer and Exercise of Stock Option.

            (a)(i) If the Offer is terminated by Purchaser for the reasons set
forth in paragraph (d) of Annex I to the Merger Agreement or (ii) in the case of
the expiration of the Offer, if the Offer expires without the purchase of Shares
thereunder and either without satisfaction of the Minimum Condition (as defined
in the Merger Agreement) or after the occurrence of circumstances giving rise to
a right of termination by Purchaser for the reasons set forth in paragraph (d)
of Annex I to the Merger Agreement, in each case without any violation of the
Offer or the Merger Agreement by Purchaser or Parent, then the Stock Option may
be exercised by Purchaser, in whole and for all of Shareholder's Shares but not
in part or for less than all of Shareholder's Shares. Notice of exercise may be
given at any time during the period (the "Exercise Period") commencing on the
date on which the Offer is terminated or expires (under the circumstances
provided in this Section 1.5) and ending on March 31, 1999, whichever is later.
In addition, Purchaser may also exercise the Stock Option if the Merger
Agreement shall terminate by reason of the Company's exercise of its termination
rights pursuant to Section 8.1(c)(ii) of the Merger Agreement, whereupon the
Exercise Period shall commence on the date such termination rights are exercised
and end on March 31, 1999, whichever is later.

            (b) In the event Purchaser wishes to exercise the Stock Option,
Purchaser shall send a written notice (an "Exercise Notice") during the Exercise
Period to the Shareholder specifying that Purchaser shall purchase the Shares
held by Shareholder and a date, which shall be a business day, and a place,
which shall be in the city of New York, for the closing of such purchase (the
"Stock Option Closing").

            (c) Upon receipt of the Exercise Notice, Shareholder shall be
obligated to deliver to Purchaser a certificate or certificates representing the
Shares held by Shareholder (or to direct the depositary for the Offer to so
deliver such certificates or certificates), in accordance with the terms of this
Agreement, on the later of the date specified in such Exercise Notice or the
first business day on which the conditions specified in Section 1.6 shall be
satisfied. The date specified in such Exercise Notice may be as early as one
business day after the date of such Exercise Notice but shall not be later than
five (5) business days after the later of (i) the date of such Exercise Notice,
or (ii) the date all conditions under Section 1.6 are satisfied.


                                      -3-
<PAGE>

      1.6 Conditions to Delivery of the Shares.

            The obligation of the Shareholder to deliver, and of the Purchaser
to pay for, the Shares upon exercise of the Stock Option is subject to the
following conditions:

            (a) All waiting periods under the Hart-Scott-Rodino Antitrust
Improvements Act of 1976, as amended, applicable to the exercise of the Stock
Option and the delivery of the Shares shall have expired or been terminated; and

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

      1.7 Stock Option Closing.

            At the Stock Option Closing, the Shareholder will deliver to
Purchaser a certificate or certificates evidencing the Shares owned by
Shareholder, each such certificate being duly endorsed in blank and accompanied
by such stock powers and such other documents as may be necessary in Purchaser's
judgment to transfer record ownership of the Shares into Purchaser's name on the
stock transfer books of the Company, and Purchaser will purchase the delivered
Shares at the Offer Price. All payments made by Purchaser to Shareholder
pursuant to this Section 1.7 shall be made by wire transfer of immediately
available funds or by certified bank check payable to Shareholder, in an amount
equal to the product of (a) the Offer Price and (b) the Shares delivered by
Shareholder in respect of the Stock Option Closing.

      1.8 Adjustments Upon Changes in Capitalization.

            In the event of any change in the number of issued and outstanding
shares of Common Stock by reason of any stock dividend, subdivision, merger,
recapitalization, combination, conversion or exchange of shares, or any other
change in the corporate or capital structure of the Company (including, without
limitation, the declaration of payment of an extraordinary dividend of cash or
securities) which would have the effect of diluting or otherwise adversely
affecting Purchaser's rights and privileges under this Agreement, the number and
kind of the shares and the consideration payable in respect to the Shares shall
be appropriately and equitably adjusted to restore to Purchaser its rights and
privileges under this Agreement. Without limiting the scope of the foregoing, in
any such event, at the option of Purchaser, the Stock Option shall represent the
right to purchase, in addition to the number and kind of Shares which Purchaser
would be entitled to purchase pursuant to the immediately preceding sentence,
whatever securities, cash or other property the Shares subject to the Stock
Option shall have been converted into or otherwise exchanged for, together with
any securities, cash or other property which shall have been distributed with
respect to such Shares.


                                      -4-
<PAGE>

2. Representations and Warranties of Shareholder.

      Shareholder hereby represents and warrants to Purchaser as follows:

      2.1 Title.

            Shareholder is the owner (both beneficially and of record or
beneficially as respects the interest of Shareholder in shares held in the
Shareholder's IRA) of the Shares. Except for the Shares and shares described in
footnote 1 on page one hereof, Shareholder is not the record or beneficial owner
of, and does not have any other rights of any nature to acquire any additional
shares of, any shares of capital stock of the Company. Shareholder will deliver,
in accordance with the terms of this Agreement, all of the Shares, free and
clear of all security interests, liens, claims, pledges, options, restrictions,
rights of first refusal, agreements, limitations on Shareholder's voting rights,
charges and other encumbrances of any nature whatsoever, and, except as provided
in this Agreement, Shareholder has not appointed or granted any proxy, which
appointment or grant is still effective, with respect to any of the Shares. The
Shareholder has sole voting power with respect to the matters set forth in
Section 6 hereof with respect to the Shares.

      2.2 Authority Relative to This Agreement.

            Shareholder has all necessary power and authority to execute and
deliver this Agreement, to perform Shareholder's obligations hereunder and to
consummate the transactions contemplated hereby. This Agreement has been duly
and validly executed and delivered by Shareholder and, assuming the due
authorization, execution and delivery by Purchaser, constitutes a legal, valid
and binding obligation of Shareholder enforceable against Shareholder in
accordance with its terms.

      2.3 No Conflict.

            The execution and delivery of this Agreement by Shareholder does
not, and the performance of this Agreement by Shareholder will not, (a) except
for any filings required under the HSR Act and for requirements of federal and
state securities laws, require any consent, approval, authorization or permit
of, or filing with or notification to, any governmental or regulatory authority,
domestic or foreign, or (b) conflict with, violate or result in any breach of or
constitute a default under (or an event which with notice or lapse of time or
both would become a default under) any agreement, judgment, injunction, order,
law, rule, regulation, decree or arrangement to which Shareholder is a party or
is bound.


                                      -5-
<PAGE>

      2.4 Brokers.

            Except for Salomon Smith Barney, whose fees will be paid by the
Company and a true and correct copy of whose engagement letter has been provided
by the Company, no broker, finder or investment banker is entitled to any
brokerage, finder's or other fee or commission in connection with the
transactions contemplated hereby based upon arrangements made by or on behalf of
Shareholder or the Company.

3. Representations and Warranties of Purchaser and Parent.

      3.1 Authority Relative to This Agreement.

            Purchaser and Parent have all necessary power and authority to
execute and deliver this Agreement, to perform its obligations hereunder and to
consummate the transactions contemplated hereby. The execution and delivery of
this Agreement by Purchaser and the consummation by Purchaser of the
transactions contemplated hereby have been duly and validly authorized by all
necessary corporate action on the part of Purchaser and Parent. This Agreement
has been duly and validly executed and delivered by Purchaser and Parent as
Guarantor, assuming the due authorization, execution and delivery by
Shareholder, constitutes a legal, valid and binding obligation of Purchaser and
Parent, enforceable against Purchaser and Parent in accordance with its terms.

      3.2 No Conflict.

            The execution and delivery of this Agreement by Purchaser and Parent
does not, and the performance of this Agreement by Purchaser and Parent will
not, (a) except for any filings required under the HSR Act and for requirements
of federal and state securities laws, require any consent, approval,
authorization or permit of, or filing with or notification to, any governmental
or regulatory authority, domestic or foreign, (b) conflict with or violate the
certificate of incorporation or bylaws of Purchaser or Parent, (c) conflict
with, violate or result in any breach of or constitute a default under (or an
event which with notice or lapse of time or both would become a default under)
any agreement, judgment, injunction, order, law, rule, regulation, decree or
arrangement applicable to Purchaser or Parent or by which any property or asset
of Purchaser or Parent is bound or affected, other than, in the case of clause
(c), any such conflicts, violations, breaches or defaults that, individually or
in the aggregate, would not materially impair the ability of Purchaser or Parent
to perform its obligations hereunder.

      3.3 Brokers.

            Except for Credit Suisse First Boston, whose fees will be paid by
Purchaser, no broker, finder or investment banker is entitled to any brokerage,
finder's or other fee or commission from Shareholder in connection with the
transactions contemplated hereby based upon arrangements made by or on behalf of
Purchaser.


                                      -6-
<PAGE>

      3.4 Investment Intent.

            Purchaser hereby represents that any securities it purchases
pursuant to this Agreement are being purchased for its own account for
investment and not with a view to, or for sale in connection with, any public
distribution thereof.

4. Covenant of Shareholder.

      No Solicitation of Transactions. Shareholder and his affiliates shall not,
and Shareholder and his affiliates shall use their best efforts to ensure that
Shareholder's representatives and agents (including, but not limited to,
investment bankers, attorneys and accountants) and his affiliates' officers,
directors, employees, representatives and agents do not, directly or indirectly,
encourage, solicit, participate in or initiate discussions or negotiations with,
or provide any information to, any corporation, partnership, person or other
entity or group (other than Purchaser or any of its affiliates or
representatives) concerning any proposal or offer to acquire all or a
substantial part of the business or properties of the Company or any of its
subsidiaries, whether by merger, tender offer, exchange offer, sale of assets or
similar transaction involving the Company or any subsidiary, division or
operating or principal business unit of the Company (an "Acquisition Proposal"),
except that the provisions of this Section 4 shall not restrict the
Shareholder's ability to act in such Shareholder's capacity as a director of the
Company in accordance with Section 6.8 of the Merger Agreement. Shareholder
shall immediately cease and cause to be terminated any existing activities,
discussions or negotiations by Shareholder or his affiliates or any investment
banker, attorney, accountant or other advisor or representative of Shareholder
or his affiliates with parties conducted heretofore with respect to any of the
foregoing.

5. Additional Covenants of Shareholder.

      5.1 No Disposition. Shareholder hereby covenants and agrees that, except
as contemplated by this Agreement and except pursuant to the Offer, Shareholder
shall not, and shall not offer or agree to, sell, transfer, tender, assign, or
otherwise dispose of, or create or permit to exist any restriction, right of
first refusal, agreement or limitation on Shareholder's voting rights, with
respect to, the Shares now owned or any other shares that may hereafter be
acquired by Shareholder.

      5.2 Compliance of Shareholder with this Agreement. Shareholder shall take
all actions and forbear from all actions, in each case, necessary in order that
(a) all of Shareholder's representations and warranties hereunder are true and
correct and (b) Shareholder fulfills all of its obligations hereunder.


                                      -7-
<PAGE>

6. Voting Agreement; Proxy of Shareholder.

      6.1 Voting Agreement.

            Shareholder hereby agrees that, during the time this Agreement is in
effect, at any meeting of the stockholders of the Company, however called, and
in any action by written consent of the stockholders of the Company, Shareholder
shall, to the extent applicable, (a) vote (or execute a consent in respect of)
all of the Shares in favor of the Merger, the Merger Agreement (as amended from
time to time) and any of the transactions contemplated by the Merger Agreement;
(b) vote (or execute a consent in respect of) the Shares against any action or
agreement that would result in a breach of any covenant, representation or
warranty or any other obligation of the Company under the Merger Agreement; and
(c) vote (or execute a consent in respect of) the Shares against any action or
agreement that would reasonably be expected to impede, interfere with, delay or
attempt to discourage the Offer or the Merger, including, but not limited to:
(i) any extraordinary corporate transaction (other than the Merger), such as a
merger, reorganization, recapitalization or liquidation involving the Company or
any of its Subsidiaries (as defined in the Merger Agreement) or any proposal
made in opposition to or in competition with the Merger; (ii) a sale or transfer
of a material amount of assets of the Company or any of its Subsidiaries; (iii)
any change in the management or board of directors of the Company, except as
otherwise agreed to in writing by Purchaser or Purchaser; (iv) any material
change in the present capitalization or dividend policy of the Company; or (v)
any other material change in the corporate structure or business of the Company
or any of its Subsidiaries.

      6.2 Irrevocable Proxy.

            Shareholder agrees that, in the event Shareholder shall fail to
comply with the provisions of Section 6.1 hereof as determined by Purchaser in
its sole discretion, such failure shall result, without any further action by
Shareholder, in the irrevocable appointment of Purchaser as the attorney and
proxy of Shareholder, with full power of substitution, to vote, and otherwise
act (by written consent or otherwise) with respect to all of the Shares that
Shareholder is entitled to vote at any meeting of stockholders of the Company
(whether annual or special and whether or not an adjourned or postponed meeting)
or consent in lieu of any such meeting or otherwise, on the matters and in the
manner specified in Section 6.1. THIS PROXY AND POWER OF ATTORNEY IS IRREVOCABLE
AND COUPLED WITH AN INTEREST AND IS EXECUTED AND INTENDED TO BE IRREVOCABLE IN
ACCORDANCE WITH THE PROVISIONS OF SECTION 212(e) OF THE DELAWARE GENERAL
CORPORATION LAW ("DGCL"). Shareholder hereby revokes, effective upon the
execution and delivery of the Merger Agreement by the parties thereto, all other
proxies and powers of attorney with respect to the Shares that Shareholder may
have heretofore appointed or granted, and no subsequent proxy or power of
attorney (except in furtherance of Shareholder's obligations under Section 6.1
hereof) shall be given or written consent executed (and if given or executed,
shall not be effective) by Shareholder with respect thereto so long as this
Agreement remains in effect.


                                      -8-
<PAGE>

7. Termination.

      Other than the Stock Option which shall be governed by Section 1.4(a)
hereof, this Agreement shall terminate automatically in the event that the
Merger Agreement is terminated in accordance with the terms and conditions
thereof.

8. Miscellaneous.

      8.1 Expenses.

            All costs and expenses incurred in connection with the transactions
contemplated by this Agreement shall be paid by the party incurring such
expenses.

      8.2 Further Assurances.

            Shareholder and Purchaser shall execute and deliver all such further
documents and instruments and take all such further action as may be necessary
in order to consummate the transactions contemplated hereby.

      8.3 Specific Performance.

            The parties hereto agree that irreparable damage would occur in the
event any provision of this Agreement were not performed in accordance with the
terms hereof and that the parties shall be entitled to specific performance of
the terms hereof, in addition to any other remedy at law or in equity.

      8.4 Entire Agreement.

            This Agreement constitutes the entire agreement between Purchaser
and Shareholder with respect to the subject matter hereof and supersedes all
prior agreements and understandings, both written and oral, between Purchaser
and Shareholder with respect to the subject matter hereof.

      8.5 Assignment.

            This Agreement shall not be assigned by operation of law or
otherwise, except that Purchaser may assign all or any of its rights hereunder
except that such assignment shall not relieve Purchaser of its obligations
hereunder if such assignee does not perform such obligations.


                                      -9-
<PAGE>

      8.6 Parties in Interest.

            This Agreement shall be binding upon, inure solely to the benefit
of, and be enforceable by, the parties hereto and their successors and permitted
assigns. Nothing in this Agreement, express or implied, is intended to or shall
confer upon any other person any right, benefit or remedy of any nature
whatsoever under or by reason of this Agreement.

      8.7 Amendment; Waiver.

            This Agreement may not be amended except by an instrument in writing
signed by the parties hereto. Any party hereto may (a) extend the time for the
performance of any obligation or other act of any other party hereto, (b) waive
any inaccuracy in the representations and warranties contained herein or in any
document delivered pursuant hereto and (c) waive compliance with any agreement
or condition contained herein. Any such extension or waiver shall be valid if
set forth in an instrument in writing signed by the party or parties to be bound
thereby.

      8.8 Severability.

            If any term or other provision of this Agreement is invalid, illegal
or incapable of being enforced by any rule of law, or public policy, all other
conditions and provisions of this Agreement shall nevertheless remain in full
force and effect so long as the economic or legal substance of this Agreement is
not affected in any manner materially adverse to any party. Upon such
determination that any term or other provision is invalid, illegal or incapable
of being enforced, the parties hereto shall negotiate in good faith to modify
this Agreement so as to effect the original intent of the parties as closely as
possible in a mutually acceptable manner in order that the terms of this
Agreement remain as originally contemplated to the fullest extent possible.

      8.9 Notices.

            All notices, requests, claims, demands and other communications
hereunder shall be in writing and shall be deemed to have been duly given when
delivered in person, by overnight courier or facsimile to the respective parties
as follows:

                  If to Purchaser:

                        PPC Acquisition Corp.
                        c/o Kluwer Academic Publishers bv
                        Spuiboulevard 50, 311GR Dordrecht
                        3300 AZ Dordrecht, The Netherlands
                        Attention: Jeffrey K. Smith

                        Fax #: (011)(31)(78) 639-2268


                                      -10-
<PAGE>

                  with a copy to:

                        Wolters Kluwer U.S. Corporation
                        161 North Clark Street
                        48th Floor
                        Chicago, Illinois 60601-3221
                        Attention: Bruce C. Lenz

                        Fax #:  (312) 425-0233

                  and to:

                        Pryor Cashman Sherman & Flynn LLP
                        410 Park Avenue
                        New York, New York 10022
                        Attention: Arnold J. Schaab, Esq.

                        Fax #:  (212) 326-0806

                  if to Shareholder:

                        Bernard Bressler
                        3 Kimberwick Court
                        Morristown, New Jersey 07960

                        Fax #:  (973) 984-1545

                  with a copy to:

                        BRESSLER, AMERY & ROSS, P.C.
                        17 State Street
                        New York, New York 10004
                        Attention: Bernard Bressler, Esq.

                        Fax #:  (212) 425-9337

      8.10 Governing Law.

            This Agreement shall be governed by, and construed in accordance
with, the laws of the State of Delaware applicable to contracts executed in and
to be performed in Delaware without regard to any principles of choice of law or
conflicts of law of such State. All actions and proceedings arising out of or
relating to this Agreement shall be heard and determined in any 


                                      -11-
<PAGE>

state or federal court sitting in Delaware. Each of the parties hereto (i)
consents to submit such party to the personal jurisdiction of any Federal court
located in the State of Delaware or any Delaware state court in the event any
dispute arises out of this Agreement or any of the transactions contemplated
hereby, (ii) agrees that such party will not attempt to deny or defeat such
personal jurisdiction by motion or other request for leave from any such court,
(iii) agrees that such party will not bring any action relating to this
Agreement or the transactions contemplated hereby in any court other than a
Federal court sitting in the state of Delaware or a Delaware state court and
(iv) waives any right to trial by jury with respect to any claim or proceeding
related to or arising out of this Agreement or any of the transactions
contemplated hereby.

      8.11 Headings.

            The descriptive headings contained in this Agreement are included
for convenience of reference only and shall not affect in any way the meaning or
interpretation of this Agreement.

      8.12 Counterparts.

            This Agreement may be executed and delivered (including by facsimile
transmission) in one or more counterparts, and by the different parties hereto
in separate counterparts, each of which when as executed and delivered shall be
deemed to be an original but all of which taken together shall constitute one
and the same agreement.


                                      -12-
<PAGE>

      IN WITNESS WHEREOF, each of the parties hereto has caused this Agreement
to be duly executed and delivered as of the date first written above.

                                    PPC ACQUISITION CORP.

                                    By: /s/ Jeffrey K. Smith
                                       ----------------------------
                                       Name:  Jeffrey K. Smith
                                       Title: President

                                    Shareholder

                                     /s/ Bernard Bressler
                                    -------------------------------
                                    Bernard Bressler


                                      -13-
<PAGE>

      Kluwer Boston, Inc. in consideration of the undertakings hereunder by
Shareholder does hereby guaranty performance of the obligations undertake herein
by Purchaser and to the extent that such guarantee shall relate to the payment
of moneys, such guaranty shall be a guaranty of performance and not a guaranty
of collection.

                                    KLUWER BOSTON, INC.


                                    By: /s/ Jeffrey K. Smith
                                       ----------------------------
                                       Name:  Jeffrey K. Smith
                                       Title: President


                                      -14-


<PAGE>

                                                          


                            STOCK PURCHASE AGREEMENT

      Stock Purchase Agreement (this "Agreement"), dated as of June 10, 1998,
between PPC Acquisition Corp. ("Purchaser") and Teresa Bressler ("Shareholder").

      WHEREAS, Shareholder owns (both beneficially and of record) 10,497 shares
of common stock, par value $.10 per share ("Common Stock") of Plenum Publishing
Corp. (the "Company")(the "Shares").

      WHEREAS, concurrently herewith, Kluwer Boston Inc. ("Parent") and
Purchaser, a wholly owned subsidiary of Parent, are entering into an agreement
and plan of merger with the Company, dated as of June 10, 1998 (the "Merger
Agreement"), pursuant to which Purchaser has agreed to make a cash tender offer
(the "Offer") for, among other things, all outstanding shares of Common Stock of
the Company at $73.50 per share (or any higher price paid in the Offer, the
"Offer Price"), net to the seller in cash, to be followed by a merger of
Purchaser with and into the Company (the "Merger"); and

      WHEREAS, as a condition to the willingness of Purchaser and Parent to
enter into the Merger Agreement, Purchaser, whose performance hereunder is
guaranteed by Parent, has required that Shareholder agree, and in order to
induce Purchaser and Parent to enter into the Merger Agreement, Shareholder has
agreed, among other things, (i) to sell the Shares; (ii) to tender the Shares
into the Offer; (iii) to appoint Purchaser as Shareholder's proxy to vote the
Shares under certain circumstances, and (iv) with respect to certain questions
put to stockholders of the Company for a vote, to vote the Shares, in each case,
in accordance with the terms and conditions of this Agreement.

      NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained herein and other good and valuable consideration, the adequacy of
which is hereby acknowledged, and intending to be legally bound hereby, the
parties hereto agree as follows:

1. Purchase and Sale of Shares.

      1.1 Tender of Shares; Purchase of Shares.

            (a) Shareholder agrees to tender and sell to Purchaser all of the
Shares pursuant to the terms of the Offer. Shareholder agrees that Shareholder
shall deliver to the depository for the Offer for receipt prior to the
Expiration Date (as defined in the Offer) of the Offer, either a letter of
transmittal together with the certificates for the Shares, if available, or a
"Notice of Guaranteed Delivery", if the Shares are not available. Unless an
election is made by Purchaser under Section 1.1(b), Shareholder agrees not to
withdraw any Shares tendered into the Offer. Upon such tender Shareholder will
be relieved of any obligation under Sec. 1.1(b) hereof.

            (b) Upon the election of Purchaser on the terms and subject to the
conditions set forth in this Agreement, on (and assuming the occurrence of) the
Closing Date (as defined herein), Purchaser will purchase from the Shareholder,
and the Shareholder will sell and transfer
<PAGE>

to the Purchaser, all of the Shares, free and clear of all mortgages, pledges,
security interest, encumbrances, liens, options, debts, charges, claims and
restrictions of any kind, at a purchase price per share equal to the Offer
Price.

      1.2 Conditions to the Closing.

            Subject to the provisions of the first sentence of Section 1.3
hereof, the obligations of the parties to consummate the transactions
contemplated by Section 1.1(b) hereof are subject to the following conditions:
(a) any waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of
1976, as amended (the "HSR Act") applicable to the delivery of the Shares and
the consummation of the Offer shall have expired or been terminated; and (b)
there shall be no preliminary or permanent injunction or other order by any
court of competent jurisdiction restricting, preventing or prohibiting the
delivery of the Shares. Purchaser and Shareholder shall each promptly after the
date hereof make such filings and provide such information as may be required
under the HSR Act with respect to the sale of the Shares.

      1.3 Closing.

            Subject to the conditions contained in this Agreement and subject to
Sections 1.4 through 1.8, the closing of the transactions contemplated by
Section 1.1(b) hereof (the "Closing") shall occur at a site designated by
Purchaser simultaneously with the acceptance by Purchaser of the shares of
Common Stock validly tendered and not withdrawn pursuant to the terms of the
Offer in accordance with the terms and conditions of the Offer and the Merger
Agreement (the "Closing Date"). At the Closing and subject to the conditions
contained in this Agreement, Purchaser hereby directs Shareholder to deliver to
Purchaser a certificate or certificates evidencing the Shares, each such
certificate being duly endorsed in blank and accompanied by such stock powers
and such other documents as may be necessary in Purchaser's judgment to transfer
record ownership of the Shares into Purchaser's name on the stock transfer books
of the Company, and Purchaser will purchase the Shares at a purchase price equal
to the Offer Price. All payments made by Purchaser to Shareholder pursuant to
this Section 1.3 shall be made by wire transfer of immediately available funds
to an account designated by Shareholder, or by certified bank check payable to
Shareholder, in an amount equal to the sum of the product of (i) the Offer Price
and (ii) the total number of Shares delivered at the Closing.

      1.4 Stock Option.

            Effective upon expiration or termination of the Offer for the
reasons set forth in Section 1.5 below, Purchaser shall have an irrevocable
option (the "Stock Option") exercisable on the terms and conditions set forth in
Section 1.5 below to purchase the Shares, at a purchase price equal to the Offer
Price.

      1.5 Termination or Expiration of Offer and Exercise of Stock Option.


                                      -2-
<PAGE>

            (a)(i) If the Offer is terminated by Purchaser for the reasons set
forth in paragraph (d) of Annex I to the Merger Agreement or (ii) in the case of
the expiration of the Offer, if the Offer expires without the purchase of Shares
thereunder and either without satisfaction of the Minimum Condition (as defined
in the Merger Agreement) or after the occurrence of circumstances giving rise to
a right of termination by Purchaser for the reasons set forth in paragraph (d)
of Annex I to the Merger Agreement, in each case without any violation of the
Offer or the Merger Agreement by Purchaser or Parent, then the Stock Option may
be exercised by Purchaser, in whole and for all of Shareholder's Shares but not
in part or for less than all of Shareholder's Shares. Notice of exercise may be
given at any time during the period (the "Exercise Period") commencing on the
date on which the Offer is terminated or expires (under the circumstances
provided in this Section 1.5) and ending on March 31, 1999, whichever is later.
In addition, Purchaser may also exercise the Stock Option if the Merger
Agreement shall terminate by reason of the Company's exercise of its termination
rights pursuant to Section 8.1(c)(ii) of the Merger Agreement, whereupon the
Exercise Period shall commence on the date such termination rights are exercised
and end on March 31, 1999, whichever is later.

            (b) In the event Purchaser wishes to exercise the Stock Option,
Purchaser shall send a written notice (an "Exercise Notice") during the Exercise
Period to the Shareholder specifying that Purchaser shall purchase the Shares
held by Shareholder and a date, which shall be a business day, and a place,
which shall be in the city of New York, for the closing of such purchase (the
"Stock Option Closing").

            (c) Upon receipt of the Exercise Notice, Shareholder shall be
obligated to deliver to Purchaser a certificate or certificates representing the
Shares held by Shareholder (or to direct the depositary for the Offer to so
deliver such certificates or certificates), in accordance with the terms of this
Agreement, on the later of the date specified in such Exercise Notice or the
first business day on which the conditions specified in Section 1.6 shall be
satisfied. The date specified in such Exercise Notice may be as early as one
business day after the date of such Exercise Notice but shall not be later than
five (5) business days after the later of (i) the date of such Exercise Notice,
or (ii) the date all conditions under Section 1.6 are satisfied.

      1.6 Conditions to Delivery of the Shares.

            The obligation of the Shareholder to deliver, and of the Purchaser
to pay for, the Shares upon exercise of the Stock Option is subject to the
following conditions:

            (a) All waiting periods under the Hart-Scott-Rodino Antitrust
Improvements Act of 1976, as amended, applicable to the exercise of the Stock
Option and the delivery of the Shares shall have expired or been terminated; and

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


                                      -3-
<PAGE>

      1.7 Stock Option Closing.

            At the Stock Option Closing, the Shareholder will deliver to
Purchaser a certificate or certificates evidencing the Shares owned by
Shareholder, each such certificate being duly endorsed in blank and accompanied
by such stock powers and such other documents as may be necessary in Purchaser's
judgment to transfer record ownership of the Shares into Purchaser's name on the
stock transfer books of the Company, and Purchaser will purchase the delivered
Shares at the Offer Price. All payments made by Purchaser to Shareholder
pursuant to this Section 1.7 shall be made by wire transfer of immediately
available funds or by certified bank check payable to Shareholder, in an amount
equal to the product of (a) the Offer Price and (b) the Shares delivered by
Shareholder in respect of the Stock Option Closing.

      1.8 Adjustments Upon Changes in Capitalization.

            In the event of any change in the number of issued and outstanding
shares of Common Stock by reason of any stock dividend, subdivision, merger,
recapitalization, combination, conversion or exchange of shares, or any other
change in the corporate or capital structure of the Company (including, without
limitation, the declaration of payment of an extraordinary dividend of cash or
securities) which would have the effect of diluting or otherwise adversely
affecting Purchaser's rights and privileges under this Agreement, the number and
kind of the shares and the consideration payable in respect to the Shares shall
be appropriately and equitably adjusted to restore to Purchaser its rights and
privileges under this Agreement. Without limiting the scope of the foregoing, in
any such event, at the option of Purchaser, the Stock Option shall represent the
right to purchase, in addition to the number and kind of Shares which Purchaser
would be entitled to purchase pursuant to the immediately preceding sentence,
whatever securities, cash or other property the Shares subject to the Stock
Option shall have been converted into or otherwise exchanged for, together with
any securities, cash or other property which shall have been distributed with
respect to such Shares.

2. Representations and Warranties of Shareholder.

      Shareholder hereby represents and warrants to Purchaser as follows:

      2.1 Title.

            Shareholder is the owner (both beneficially and of record) of the
Shares. Except for the Shares, Shareholder is not the record or beneficial owner
of, and does not have any other rights of any nature to acquire any additional
shares of, any shares of capital stock of the Company. Shareholder will deliver
in accordance with the terms of this Agreement all of the Shares, free and clear
of all security interests, liens, claims, pledges, options, restrictions, rights
of first refusal, agreements, limitations on Shareholder's voting rights,
charges and other encumbrances of any nature whatsoever, and, except as provided
in this Agreement, Shareholder 


                                      -4-
<PAGE>

has not appointed or granted any proxy, which appointment or grant is still
effective, with respect to any of the Shares. The Shareholder has sole voting
power with respect to the matters set forth in Section 6 hereof with respect to
the Shares.

      2.2 Authority Relative to This Agreement.

            Shareholder has all necessary power and authority to execute and
deliver this Agreement, to perform Shareholder's obligations hereunder and to
consummate the transactions contemplated hereby. This Agreement has been duly
and validly executed and delivered by Shareholder and, assuming the due
authorization, execution and delivery by Purchaser, constitutes a legal, valid
and binding obligation of Shareholder enforceable against Shareholder in
accordance with its terms.

      2.3 No Conflict.

            The execution and delivery of this Agreement by Shareholder does
not, and the performance of this Agreement by Shareholder will not, (a) except
for any filings required under the HSR Act and for requirements of federal and
state securities laws, require any consent, approval, authorization or permit
of, or filing with or notification to, any governmental or regulatory authority,
domestic or foreign, or (b) conflict with, violate or result in any breach of or
constitute a default under (or an event which with notice or lapse of time or
both would become a default under) any agreement, judgment, injunction, order,
law, rule, regulation, decree or arrangement to which Shareholder is a party or
is bound.

      2.4 Brokers.

            Except for Salomon Smith Barney, whose fees will be paid by the
Company and a true and correct copy of whose engagement letter has been provided
by the Company, no broker, finder or investment banker is entitled to any
brokerage, finder's or other fee or commission in connection with the
transactions contemplated hereby based upon arrangements made by or on behalf of
Shareholder or the Company.

3. Representations and Warranties of Purchaser and Parent.

      3.1 Authority Relative to This Agreement.

            Purchaser has all necessary power and authority to execute and
deliver this Agreement, to perform its obligations hereunder and to consummate
the transactions contemplated hereby. The execution and delivery of this
Agreement by Purchaser and the consummation by Purchaser of the transactions
contemplated hereby have been duly and validly authorized by all necessary
corporate action on the part of Purchaser and Parent. This Agreement has been
duly and validly executed and delivered by Purchaser and Parent as Guarantor,
assuming the due authorization, execution and delivery by Shareholder,
constitutes a


                                      -5-
<PAGE>

legal, valid and binding obligation of Purchaser and Parent, enforceable against
Purchaser and Parent in accordance with its terms.

      3.2 No Conflict.

            The execution and delivery of this Agreement by Purchaser and Parent
does not, and the performance of this Agreement by Purchaser and Parent will
not, (a) except for any filings required under the HSR Act and for requirements
of federal and state securities laws, require any consent, approval,
authorization or permit of, or filing with or notification to, any governmental
or regulatory authority, domestic or foreign, (b) conflict with or violate the
certificate of incorporation or bylaws of Purchaser or Parent, (c) conflict
with, violate or result in any breach of or constitute a default under (or an
event which with notice or lapse of time or both would become a default under)
any agreement, judgment, injunction, order, law, rule, regulation, decree or
arrangement applicable to Purchaser or Parent or by which any property or asset
of Purchaser or Parent is bound or affected, other than, in the case of clause
(c), any such conflicts, violations, breaches or defaults that, individually or
in the aggregate, would not materially impair the ability of Purchaser or Parent
to perform its obligations hereunder.

      3.3 Brokers.

            Except for Credit Suisse First Boston, whose fees will be paid by
Purchaser, no broker, finder or investment banker is entitled to any brokerage,
finder's or other fee or commission from Shareholder in connection with the
transactions contemplated hereby based upon arrangements made by or on behalf of
Purchaser.

      3.4 Investment Intent.

            Purchaser hereby represents that any securities it purchases
pursuant to this Agreement are being purchased for its own account for
investment and not with a view to, or for sale in connection with, any public
distribution thereof.

4. Covenant of Shareholder.

      No Solicitation of Transactions. Shareholder and his affiliates shall not,
and Shareholder and his affiliates shall use their best efforts to ensure that
Shareholder's representatives and agents (including, but not limited to,
investment bankers, attorneys and accountants) and his affiliates' officers,
directors, employees, representatives and agents do not, directly or indirectly,
encourage, solicit, participate in or initiate discussions or negotiations with,
or provide any information to, any corporation, partnership, person or other
entity or group (other than Purchaser or any of its affiliates or
representatives) concerning any proposal or offer to acquire all or a
substantial part of the business or properties of the Company or any of its
subsidiaries, whether by merger, tender offer, exchange offer, sale of assets or
similar transaction involving the Company or any subsidiary, division or
operating or principal business unit of the Company 


                                      -6-
<PAGE>

(an "Acquisition Proposal"). Shareholder shall immediately cease and cause to be
terminated any existing activities, discussions or negotiations by Shareholder
or his affiliates or any investment banker, attorney, accountant or other
advisor or representative of Shareholder or his affiliates with parties
conducted heretofore with respect to any of the foregoing.

5. Additional Covenants of Shareholder.

      5.1 No Disposition. Shareholder hereby covenants and agrees that, except
as contemplated by this Agreement and except pursuant to the Offer, Shareholder
shall not, and shall not offer or agree to, sell, transfer, tender, assign,
hypothecate or otherwise dispose of, or create or permit to exist any option,
restriction, right of first refusal, agreement or limitation on Shareholder's
voting rights, with respect to, the Shares now owned or any other shares that
may hereafter be acquired by Shareholder.

      5.2 Compliance of Shareholder with this Agreement. Shareholder shall take
all actions and forbear from all actions, in each case, necessary in order that
(a) all of Shareholder's representations and warranties hereunder are true and
correct and (b) Shareholder fulfills all of its obligations hereunder.

6. Voting Agreement; Proxy of Shareholder.

      6.1 Voting Agreement.

            Shareholder hereby agrees that, during the time this Agreement is in
effect, at any meeting of the stockholders of the Company, however called, and
in any action by written consent of the stockholders of the Company, Shareholder
shall, to the extent applicable, (a) vote (or execute a consent in respect of)
all of the Shares in favor of the Merger, the Merger Agreement (as amended from
time to time) and any of the transactions contemplated by the Merger Agreement;
(b) vote (or execute a consent in respect of) the Shares against any action or
agreement that would result in a breach of any covenant, representation or
warranty or any other obligation of the Company under the Merger Agreement; and
(c) vote (or execute a consent in respect of) the Shares against any action or
agreement that would reasonably be expected to impede, interfere with, delay or
attempt to discourage the Offer or the Merger, including, but not limited to:
(i) any extraordinary corporate transaction (other than the Merger), such as a
merger, reorganization, recapitalization or liquidation involving the Company or
any of its Subsidiaries (as defined in the Merger Agreement) or any proposal
made in opposition to or in competition with the Merger; (ii) a sale or transfer
of a material amount of assets of the Company or any of its Subsidiaries; (iii)
any change in the management or board of directors of the Company, except as
otherwise agreed to in writing by Purchaser or Purchaser; (iv) any material
change in the present capitalization or dividend policy of the Company; or (v)
any other material change in the corporate structure or business of the Company
or any of its Subsidiaries.

      6.2 Irrevocable Proxy.


                                      -7-
<PAGE>

            Shareholder agrees that, in the event Shareholder shall fail to
comply with the provisions of Section 6.1 hereof as determined by Purchaser in
its sole discretion, such failure shall result, without any further action by
Shareholder, in the irrevocable appointment of Purchaser as the attorney and
proxy of Shareholder, with full power of substitution, to vote, and otherwise
act (by written consent or otherwise) with respect to all of the Shares that
Shareholder is entitled to vote at any meeting of stockholders of the Company
(whether annual or special and whether or not an adjourned or postponed meeting)
or consent in lieu of any such meeting or otherwise, on the matters and in the
manner specified in Section 6.1. THIS PROXY AND POWER OF ATTORNEY IS IRREVOCABLE
AND COUPLED WITH AN INTEREST AND IS EXECUTED AND INTENDED TO BE IRREVOCABLE IN
ACCORDANCE WITH THE PROVISIONS OF SECTION 212(e) OF THE DELAWARE GENERAL
CORPORATION LAW ("DGCL"). Shareholder hereby revokes, effective upon the
execution and delivery of the Merger Agreement by the parties thereto, all other
proxies and powers of attorney with respect to the Shares that Shareholder may
have heretofore appointed or granted, and no subsequent proxy or power of
attorney (except in furtherance of Shareholder's obligations under Section 6.1
hereof) shall be given or written consent executed (and if given or executed,
shall not be effective) by Shareholder with respect thereto so long as this
Agreement remains in effect.

7. Termination.

      Other than the Stock Option which shall be governed by Section 1.4(a)
hereof, this Agreement shall terminate automatically in the event that the
Merger Agreement is terminated in accordance with the terms and conditions
thereof.

8. Miscellaneous.

      8.1 Expenses.

            All costs and expenses incurred in connection with the transactions
contemplated by this Agreement shall be paid by the party incurring such
expenses.

      8.2 Further Assurances.

            Shareholder and Purchaser shall execute and deliver all such further
documents and instruments and take all such further action as may be necessary
in order to consummate the transactions contemplated hereby.


                                      -8-
<PAGE>

      8.3 Specific Performance.

            The parties hereto agree that irreparable damage would occur in the
event any provision of this Agreement were not performed in accordance with the
terms hereof and that the parties shall be entitled to specific performance of
the terms hereof, in addition to any other remedy at law or in equity.

      8.4 Entire Agreement.

            This Agreement constitutes the entire agreement between Purchaser
and Shareholder with respect to the subject matter hereof and supersedes all
prior agreements and understandings, both written and oral, between Purchaser
and Shareholder with respect to the subject matter hereof.

      8.5 Assignment.

            This Agreement shall not be assigned by operation of law or
otherwise, except that Purchaser may assign all or any of its rights hereunder
except that such assignment shall not relieve Purchaser of its obligations
hereunder if such assignee does not perform such obligations.

      8.6 Parties in Interest.

            This Agreement shall be binding upon, inure solely to the benefit
of, and be enforceable by, the parties hereto and their successors and permitted
assigns. Nothing in this Agreement, express or implied, is intended to or shall
confer upon any other person any right, benefit or remedy of any nature
whatsoever under or by reason of this Agreement.

      8.7 Amendment; Waiver.

            This Agreement may not be amended except by an instrument in writing
signed by the parties hereto. Any party hereto may (a) extend the time for the
performance of any obligation or other act of any other party hereto, (b) waive
any inaccuracy in the representations and warranties contained herein or in any
document delivered pursuant hereto and (c) waive compliance with any agreement
or condition contained herein. Any such extension or waiver shall be valid if
set forth in an instrument in writing signed by the party or parties to be bound
thereby.

      8.8 Severability.

            If any term or other provision of this Agreement is invalid, illegal
or incapable of being enforced by any rule of law, or public policy, all other
conditions and provisions of this Agreement shall nevertheless remain in full
force and effect so long as the economic or legal substance of this Agreement is
not affected in any manner materially adverse to any party. Upon 


                                      -9-
<PAGE>

such determination that any term or other provision is invalid, illegal or
incapable of being enforced, the parties hereto shall negotiate in good faith to
modify this Agreement so as to effect the original intent of the parties as
closely as possible in a mutually acceptable manner in order that the terms of
this Agreement remain as originally contemplated to the fullest extent possible.

      8.9 Notices.

            All notices, requests, claims, demands and other communications
hereunder shall be in writing and shall be deemed to have been duly given when
delivered in person, by overnight courier or facsimile to the respective parties
as follows:

                  If to Purchaser:

                        PPC Acquisition Corp.
                        c/o Kluwer Academic Publishers bv
                        Spuiboulevard 50, 311GR Dordrecht
                        3300 AZ Dordrecht, The Netherlands
                        Attention: Jeffrey K. Smith

                        Fax #: (011)(31)(78) 639-2268

                  with a copy to:

                        Wolters Kluwer U.S. Corporation
                        161 North Clark Street
                        48th Floor
                        Chicago, Illinois 60601-3221
                        Attention: Bruce C. Lenz

                        Fax #:  (312) 425-0233


                                      -10-
<PAGE>

                  and to:

                        Pryor Cashman Sherman & Flynn LLP
                        410 Park Avenue
                        New York, New York 10022
                        Attention: Arnold J. Schaab, Esq.

                        Fax #:  (212) 326-0806

                  if to Shareholder:

                        Teresa Bressler
                        3 Kimberwick Court
                        Morristown, New Jersey 07960
                        Fax #: (973) 984-1545

                  with a copy to:

                        BRESSLER, AMERY & ROSS, P.C.
                        17 State Street
                        New York, New York 10004
                        Attention: Bernard Bressler, Esq.
                        Fax #: (212) 425-9337

      8.10 Governing Law.

            This Agreement shall be governed by, and construed in accordance
with, the laws of the State of Delaware applicable to contracts executed in and
to be performed in Delaware without regard to any principles of choice of law or
conflicts of law of such State. All actions and proceedings arising out of or
relating to this Agreement shall be heard and determined in any state or federal
court sitting in Delaware. Each of the parties hereto (i) consents to submit
such party to the personal jurisdiction of any Federal court located in the
State of Delaware or any Delaware state court in the event any dispute arises
out of this Agreement or any of the transactions contemplated hereby, (ii)
agrees that such party will not attempt to deny or defeat such personal
jurisdiction by motion or other request for leave from any such court, (iii)
agrees that such party will not bring any action relating to this Agreement or
the transactions contemplated hereby in any court other than a Federal court
sitting in the state of Delaware or a Delaware state court and (iv) waives any
right to trial by jury with respect to any claim or proceeding related to or
arising out of this Agreement or any of the transactions contemplated hereby.


                                      -11-
<PAGE>

      8.11 Headings.

            The descriptive headings contained in this Agreement are included
for convenience of reference only and shall not affect in any way the meaning or
interpretation of this Agreement.

      8.12 Counterparts.

            This Agreement may be executed and delivered (including by facsimile
transmission) in one or more counterparts, and by the different parties hereto
in separate counterparts, each of which when as executed and delivered shall be
deemed to be an original but all of which taken together shall constitute one
and the same agreement.


                                      -12-
<PAGE>

      IN WITNESS WHEREOF, each of the parties hereto has caused this Agreement
to be duly executed and delivered as of the date first written above.

                                    PPC ACQUISITION CORP.


                                    By: /s/ Jeffrey K. Smith
                                       ----------------------------
                                       Name:  Jeffrey K. Smith
                                       Title: President

                                    Shareholder

                                       /s/ Teresa Bressler
                                    -------------------------------
                                    Teresa Bressler


                                      -13-
<PAGE>

      Kluwer Boston, Inc. in consideration of the undertakings hereunder by
Shareholder does hereby guaranty performance of the obligations undertake herein
by Purchaser and to the extent that such guarantee shall relate to the payment
of moneys, such guaranty shall be a guaranty of performance and not a guaranty
of collection.

                                    KLUWER BOSTON, INC.


                                    By: /s/ Jeffrey K. Smith
                                       ----------------------------
                                       Name:  Jeffrey K. Smith
                                       Title: President


                                      -14-



<PAGE>

                                                         


                             STOCK OPTION AGREEMENT

      STOCK OPTION AGREEMENT, dated June 10, 1998, by and between Plenum
Publishing Corporation, a Delaware corporation (the "Company"), and Kluwer
Boston, Inc., a Massachusetts corporation (the "Purchaser").

      WHEREAS, as a condition to its willingness to enter into the Agreement and
Plan of Merger, dated as of June 10, 1998, among the Company, the Purchaser and
PPC Acquisition Corp., a Delaware corporation ("Acquisition Corp.") (the "Merger
Agreement"), Purchaser has required that the Company agree, and the Company has
agreed, to grant the Purchaser the option as set forth herein to purchase up to
698,540 shares of the common stock, $.10 par value per share, of the Company
(the "Common Stock").

      NOW, THEREFORE, to induce Purchaser to enter into the Merger Agreement,
and in consideration of Purchaser doing so and of the mutual covenants and
agreements set forth herein, the parties agree as follows:

      1. Grant of Option. The Company hereby grants to the Purchaser an
irrevocable option (the "Stock Option") to purchase up to 698,540 shares of
Common Stock ("Option Shares") at a price per share of $73.50 ("Option Price")
payable in cash.

      2. Exercise of the Stock Option. (a) The Stock Option may be exercised, in
whole or in part, at any time and from time to time after any Triggering Event
(as defined in Section 3) shall have occurred and prior to the expiration
thereof, provided that (i) all waiting periods under the Hart-Scott-Rodino
Antitrust Improvements Act of 1976 (the "HSR Act") required for the purchase of
the Option Shares shall have expired or been waived, (ii) no breach by Purchaser
or Acquisition Corp. shall have occurred and be continuing under this Agreement
or the Merger Agreement and (iii) there shall not be in effect any preliminary
or final injunction or other order issued by any court or governmental,
administrative or regulatory agency or authority, prohibiting the issuance of
the Option Shares pursuant to this Agreement. The Stock Option shall expire upon
the earlier of (I) the date of consummation of the merger with Acquisition Corp.
contemplated by the Merger Agreement, (II) twenty (20) days after the date of
consummation of any Superior Proposal or Acquisition Proposal (as such terms are
defined in the Merger Agreement) under circumstances which obligate the Company
to pay the Termination Fee (as defined in the Merger Agreement) under the terms
of the Merger Agreement, or (III) the date upon which the Merger Agreement is
terminated other than in connection with the occurrence of a Triggering Event.

            (b) If the Purchaser wishes to exercise the Stock Option for all or
some of the Option Shares, the Purchaser shall send a written notice (the
"Notice") to the 
<PAGE>

Company specifying the number of Option Shares it will purchase pursuant to such
exercise and the place and date not less than three (3) nor more than twenty
(20) days from the date of the Notice for the closing of such purchase.

      3. Triggering Event. For purposes of this Agreement, a "Triggering Event"
shall mean the occurrence of an event which requires the payment of the
Termination Fee (as defined in the Merger Agreement) by the Company to
Acquisition Corp. in accordance with the provisions of Section 6.8, 8.1 or 8.3
of the Merger Agreement.

      4. Closing. (a) At any closing on the date specified under Section 2
hereof, (i) the Purchaser will make payment to the Company of the aggregate
price for the Option Shares being purchased upon exercise of the Stock Option by
wire transfer in immediately available funds and (ii) the Company will deliver
to the Purchaser a certificate or certificates representing the number of shares
of Common Stock so purchased in the denominations designated by the Purchaser
and receipt evidencing payment of any requisite stock transfer taxes. At any
such closing, the Company shall deliver a certificate to the Purchaser
certifying that the representations and warranties made in Section 6 herein are
true and correct as of the date of such closing, and the Purchaser shall deliver
a letter to the Company agreeing that the Purchaser will not offer to sell, or
otherwise dispose of, any Option Shares acquired by it pursuant to this
Agreement in violation of the Securities Act of 1933, as amended (the "1933
Act"), and applicable state securities laws.

            (b) The closing shall take place at the location set forth in the
Notice delivered in accordance with Section 2 hereof.

      5. Covenants. (a) Upon the request of the Purchaser, the Company agrees to
file, as promptly as practicable, a registration statement and use its best
efforts to cause such registration statement to become effective, as
expeditiously as possible, under the 1933 Act and any applicable state
securities laws with respect to any proposed disposition by the Purchaser of the
Option Shares, or any portion thereof, unless, in the written opinion of counsel
to the Company, addressed to the Purchaser, registration is not required for the
proposed disposition of such Option Shares; provided, however, that the Company
shall not be obligated to file more than one registration statement (under
federal and, if applicable, state law) with respect to the Option Shares
pursuant to this paragraph. The Company agrees further to cause such
registration statement to remain effective for a reasonable period of time
required for the disposition by the Purchaser of the Option Shares in a public
offering thereof (provided, that the effectiveness of the registration statement
may be delayed or suspended for a reasonable period of time, but not in excess
of 180 days, to permit the Company to consummate (i) an offering of securities,
or (ii) extraordinary transactions that it would otherwise be precluded from
completing due to the obligations of the Company under this Section 5(a)), to
prepare and file such amendments and supplements to such registration statement
and the prospectus used in connection therewith as may be necessary to keep such
registration statement effective and to comply with the provisions of the 1933
Act with respect to the sale or other 


                                       2
<PAGE>

disposition of all securities covered by such registration statement, and to
enter into customary agreements for a secondary offering of shares (including an
underwriting agreement for a secondary offering of shares in customary form
containing customary indemnification provisions). The registration effected
under this paragraph 5(a) shall be effected at the Company's expense.

            (b) Upon the request of the Purchaser, the Company agrees that it
will promptly file applications to list any Option Shares, whether issued or
unissued, on the NASDAQ National Market System and will use its best efforts to
obtain approval of such listing.

            (c) Upon the request of Purchaser prior to Purchaser's exercise of
the Stock Option, the Company shall use its reasonable best efforts to file as
soon as practicable notifications under the HSR Act with respect to Purchaser's
exercise of the Stock Option and to respond as promptly as practicable to any
inquiries received from the Federal Trade Commission and the Antirust Division
of the Department of Justice for additional information or documentation and to
respond as promptly as practicable to all inquiries and requests received from
any State Attorney General or other Governmental Entity (as defined in the
Merger Agreement) in connection with antitrust matters. Each of the Company and
Purchaser shall further take all reasonable actions necessary to file any other
forms or notifications which may be required by any foreign Governmental Entity
and to obtain any approvals which may be required in connection therewith.

            (d) In furtherance and not in limitation of the foregoing, each of
Purchaser and the Company shall use its reasonable best efforts to resolve such
objections, if any, as may be asserted with respect to the transactions
contemplated by this Agreement under any antitrust, competition or trade
regulatory laws, rules or regulations of any domestic or foreign government or
Governmental Entity or any multinational authority ("Antitrust Laws"); provided,
however, that nothing in this Agreement shall require, or be construed to
require, Purchaser or the Company or any of their respective affiliates to
proffer to, or agree to, sell or hold separate and agree to sell, before or
after the exercise of the Stock Option, any material assets, business, or
interest in any assets or businesses of Purchaser, the Company or any of their
respective affiliates (or to consent to any sale, or agreement to sell, by the
Company of any of its material assets or businesses) or to agree to any material
changes or restrictions in the operations of any such assets or businesses.

            (e) Any party hereto shall promptly inform the other of any material
communication from the United States Federal Trade Commission, the Department of
Justice or any other domestic or foreign government or Governmental Entity or
multinational authority regarding any of the transactions contemplated by this
Agreement. If any party or any affiliate thereof receives a request for
additional information or documentary material from any such government or
authority with respect to the transactions contemplated by this Agreement, then
such party will endeavor in good faith to make, or cause to be made, as soon as
reasonably practicable and after consultation with the other party, an
appropriate response in compliance with such 


                                       3
<PAGE>

request. Purchaser will advise the Company promptly in respect of any
understandings, undertakings or agreements (oral or written) which Purchaser
proposes to make or enter into with the Federal Trade Commission, the Department
of Justice or any other domestic or foreign government or Governmental Entity or
multinational authority in connection with the transactions contemplated by this
Agreement.

      6. Representations and Warranties of the Company. The Company hereby
represents and warrants to the Purchaser as follows:

            (a) The Company is a corporation duly organized and validly existing
in good standing under the laws of Delaware. The Company has all requisite
corporate power and authority to enter into and perform all of its obligations
under this Agreement. The execution, delivery and performance of this Agreement
and all the transactions contemplated hereby have been duly authorized by the
Company's Board of Directors and no other corporate proceedings on the part of
the Company are necessary to authorize this Agreement or any of the transactions
contemplated hereby. This Agreement has been duly executed and delivered by a
duly authorized officer of the Company, and constitutes a legal, valid and
binding agreement of the Company, and assuming this Agreement is a legal, valid
and binding obligation of the Purchaser, this Agreement is enforceable against
it in accordance with its terms.

            (b) Except for compliance with the requirements of the HSR Act, no
consent of any court or governmental authority, national securities exchange
automated securities quotation system or other person is necessary for the
execution, delivery and performance of this Agreement by the Company.

            (c) The Company has taken all necessary corporate action to
authorize and reserve for issuance upon exercise of the Stock Option 698,540
authorized but unissued Common Shares. The Option Shares have been duly
authorized and, when issued and paid for in accordance with the terms of this
Agreement, will be validly issued, fully paid and nonassessable. Upon delivery
of the Option Shares to the Purchaser upon the exercise of the Option granted
under this Agreement, the Purchaser will receive good and marketable title to
the Option Shares, free and clear of any pledge, lien, security interest,
charge, preemptive right, claim, equity or encumbrance of any kind.

            (d) The execution and delivery of this Agreement do not, and the
performance of this Agreement will not, (i) violate the certificate of
incorporation or by-laws of the Company, or (ii) conflict with or result in a
breach of any terms or provisions of, or constitute a default or give rise to a
right of acceleration under, or result in the creation or imposition of any
lien, charge or encumbrance upon any property or assets of the Company under any
indenture, mortgage, loan agreement or other agreement or instrument to which
the Company is a party or by which any of its property is bound or any existing
applicable law, rule, regulation, judgment, order or decree of any governmental
instrumentality, court or national securities exchange having jurisdiction over
the Company or any of its property.


                                       4
<PAGE>

      7. Representations and Warranties of the Purchaser. The Purchaser hereby
represents and warrants to the Company that it is a corporation duly organized
and validly existing in good standing under the laws of the State of
Massachusetts and has all requisite corporate power and authority to enter into
and perform all of its obligations under this Agreement; the execution, delivery
and performance of this Agreement by it and all of the transactions contemplated
hereby have been duly authorized by all necessary corporate action on its part,
and this Agreement has been duly executed and delivered by it.

      8. Representations and Warranties to Survive Delivery. All representations
and warranties contained in this Agreement, or contained in certificates of
officers of the Company submitted pursuant to this Agreement, shall survive
delivery of and payment for the Option Shares for a period expiring on the
earlier of (a) the first anniversary of the date of delivery and payment for the
Option Shares and (b) the date upon which Purchaser shall have sold or otherwise
disposed of all of the Option Shares (other than to a direct or indirect
majority-owned subsidiary of Purchaser).

      9. Adjustment Upon Changes in Capitalization. In the event of any change
in the Common Shares by reason of stock dividends, split-ups, recapitalizations,
combinations, exchanges of shares or the like, the number of Option Shares and
the purchase price per share shall be adjusted appropriately.

      10. No Assignment. Neither the rights nor the obligations of any party
hereto may be transferred or assigned without the written consent of the other
parties, except that Purchaser may assign its rights and obligations to any
direct or indirect majority-owned subsidiary of Purchaser.

      11. Specific Performance. The parties hereto acknowledge that damages
would be an inadequate remedy for a breach of this Agreement and that the
obligations of the parties hereto shall be specifically enforceable.

      12. Entire Agreement. This Agreement and the Merger Agreement constitute
the entire agreement among the parties with respect to the subject matter hereof
and supersede all other prior agreements and understandings, both written and
oral, among the parties or any of them with respect to the subject matter
hereof.

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

      14. Further Assurances. Each party will execute and deliver all such
further documents and instruments and take all such further action as may be
necessary in order to consummate the transactions contemplated hereby.


                                       5
<PAGE>

      15. Notices. All notices, requests, claims, demands and other
communications hereunder shall be in writing and shall be deemed to have been
duly given when delivered in person, by overnight courier or facsimile to the
respective parties as follows:

      If to Purchaser:

            Kluwer Boston, Inc.
            c/o Kluwer Academic Publishers bv
            Spuiboulevard 50
            3300 AZ Dordrecht, the Netherlands
            Attention:  Jeffrey K. Smith
            Facsimile: 011-31-78-63-92-268

      with a copy to:

            Wolters Kluwer U.S. Corporation
            161 North Clark Street
            48th Floor
            Chicago, Illinois 60601-3221
            Attention: Bruce C. Lenz
            Facsimile: (312) 425-0233

      and to:

            Pryor Cashman Sherman & Flynn LLP
            410 Park Avenue
            New York, New York 10022
            Attention: Arnold J. Schaab, Esq.
            Facsimile: (212) 326-0806

      If to the Company:

            Plenum Publishing Corporation
            233 Spring Street
            New York, New York 10013
            Attention: Martin E. Tash
            Facsimile: (212) 463-0742

      with copies to:

            Bressler, Amery & Ross, P.C.
            17 State Street
            New York, New York 10004
            Attention: Bernard Bressler, Esq.
            Facsimile: (212) 425-9337


                                       6
<PAGE>

or to such other address as the person to whom notice is given may have
previously furnished to the other in writing in the manner set forth above
(provided that notice of any change of address shall be effective only upon
receipt thereof).

      16. Governing Law. This Agreement shall be governed by and construed in
accordance with the laws of the State of Delaware, regardless of the laws that
might otherwise govern under applicable principles of conflict of laws thereof.

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

      18. Parties in Interest. This Agreement shall be binding upon and inure
solely to the benefit of each party hereto, and nothing in this Agreement,
express or implied, is intended to confer upon any other person any rights or
remedies of any nature whatsoever under or by reason of this Agreement.

      19. Counterparts. This Agreement may be executed in two or more
counterparts, each of which shall be deemed to be an original, but all of which
shall constitute one and the same agreement.

      20. Expenses. Except as otherwise provided in Section 5, all costs and
expenses incurred in connection with the transactions contemplated by this
Agreement shall be paid by the party incurring such expenses.


                                       7
<PAGE>

      IN WITNESS WHEREOF, each of the parties has caused this Agreement to be
executed on its behalf by its officers thereunto duly authorized as of the day
and year first above written.

                          PLENUM PUBLISHING CORPORATION


                          By: /s/ Martin E. Tash
                             -------------------------------------------
                                 Martin E. Tash
                                 President and Chairman of the Board


                          KLUWER BOSTON, INC.


                          By:  /s/ Jeffrey K. Smith
                             -------------------------------------------
                                 Name:  Jeffrey K. Smith
                                 Title: President


                                       8


<PAGE>

                                                           


                [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


<PAGE>

                                                          


                                                                   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 

<PAGE>


("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

<PAGE>


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 

<PAGE>


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

<PAGE>


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. 

<PAGE>


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.

<PAGE>


        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


<PAGE>

                                                               Exhibit 99(C)(10)


[LOGO]

                                   June 4, 1998

Kluwer Boston, Inc.
c/o Wolters Kluwer U.S. Corporation
48th Floor
161 North Clark Street
Chicago, Illinois  60601

Dear Sirs:

     This will acknowledge the offer made by Kluwer Boston, Inc. ("Kluwer") to
purchase all of the outstanding shares of capital stock of Plenum Publishing
Corporation ("Plenum") at a price of $73.50 per share.  The Plenum Board of
Directors will meet and act on that offer on Wednesday, June 10, 1998.

     To induce Kluwer to keep its offer open until the Plenum merger agreement,
lock up agreements, option agreement and other aspects of the transaction
(collectively, the "Transaction Documents") are completed and signed, Plenum
hereby agrees that neither it nor any of its officers, directors, advisors or
other representatives will, prior to the earlier of the date on which all of the
Transaction Documents are executed and delivered by the parties or 11:59 p.m.,
Eastern Daylight time on June 24, 1998, solicit, initiate, encourage or
consider, or place before the Plenum Board of Directors, any other  bids,
offers, proposals or negotiate with anyone other than Kluwer, in respect of the
acquisition of any or all of the assets, business or capital stock of Plenum.

     Kluwer hereby agrees to keep its offer open until such earlier date.

                                   Very truly yours,

                                   /s/ Bernard Bressler
                                   -----------------------------------
                                   Bernard Bressler
                                   Secretary and Director
                                   Plenum Publishing Corporation

Accepted and agreed:
Kluwer Boston, Inc.
By Wolters Kluwer U.S. Corporation

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




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