IGEN INC /CA/
8-A12G, 1996-12-10
PATENT OWNERS & LESSORS
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<PAGE>
 
                     SECURITIES AND EXCHANGE COMMISSION

                           Washington, D.C.  20549


                                  FORM 8-A
                                        
              FOR REGISTRATION OF CERTAIN CLASSES OF SECURITIES
                   PURSUANT TO SECTION 12(b) or (g) OF THE
                       SECURITIES EXCHANGE ACT OF 1934



                          IGEN International, Inc.
              ------------------------------------------------
                        (Exact name of registrant as
                          specified in its charter)


                     Delaware                           94-2852543
         ------------------------------------------------------------
         (State of incorporation or                (I.R.S. Employer
             organization)                        Identification No.)


                1620 Industrial Drive, Gaithersburg, MD 20877
        -------------------------------------------------------------
            (Address of principal executive offices)  (Zip Code)


Securities to be registered pursuant to Section 12(b) of the Act:

     Name of each exchange on       Title of each class to
     which each class is to be      be so registered
                                    ----------------------
     registered
     ----------------------------

               None


Securities to be registered pursuant to Section 12(g) of the Act:

                       Preferred Share Purchase Rights
        ------------------------------------------------------------
                              (Title of class)

                                       1.
<PAGE>
 
Item 1.   Description of Registrant's Securities
          to be Registered.
          --------------------------------------

     Each Preferred Share Purchase Right (a "Right") entitles the registered
holder to purchase from the Company one one-hundredth of a share of Series A
Junior Participating Preferred Stock, par value $.001 per share (the "Preferred
Shares"), of the Company at a price of $65.00 per one one-hundredth of a
Preferred Share (the "Purchase Price"), subject to adjustment.  The description
and terms of the Rights are set forth in the Rights Agreement dated as of
November 6, 1996 (the "Rights Agreement"), between the Company and The First
National Bank of Boston as Rights Agent (the "Rights Agent").

     Initially, the Rights will be evidenced by the stock certificates
representing Common Shares then outstanding, and no separate Right Certificates,
as defined, will be distributed.  Until the earlier to occur of (i) the
acquisition by a person or group of affiliated or associated persons, (other
than (A) the Company, (B) a majority owned subsidiary of the Company, (C) any
employee benefit plan of the Company or any majority-owned subsidiary of the
Company, (D) any entity holding Common Shares for or pursuant to the terms of
any such plan or (E) Mr. Samuel J. Wohlstadter, his affiliates and associates,
his heirs, and any trust or foundation to which he has transferred or may
transfer Common Shares of the Company ("Samuel Wohlstadter") and each of the
persons listed in (A) through (E) above, an "excepted person") of beneficial
ownership of 15% or more of the outstanding Common Shares (an "Acquiring
Person") or (ii) 10 business days (or such later date as may be determined by
action of the Board of Directors prior to such time as any person or group of
affiliated persons becomes an Acquiring Person) following the commencement of,
or announcement of an intention to make, a tender offer or exchange offer the
consummation of which would result in the beneficial ownership by a person or
group of 15% or more of the outstanding Common Shares (the earlier of such dates
being called the "Distribution Date"), the Rights will be evidenced, with
respect to any of the Common Share certificates outstanding as of the Record
Date, by such Common Share certificate with a copy of this Summary of Rights
attached thereto.

     The Rights Agreement provides that, until the Distribution Date (or earlier
redemption or expiration of the Rights), the Rights will be transferred with and
only with the Common Shares.  Until the Distribution Date (or earlier redemption
or expiration of the Rights), new Common Share certificates issued after the
Record Date upon transfer or new issuance of Common Shares will contain a
notation incorporating the Rights Agreement by reference.  Until the
Distribution Date (or earlier redemption or expiration of the Rights) the
surrender or transfer of any certificates for Common Shares outstanding as of
the Record Date will also constitute the transfer of the Rights associated with
the Common Shares represented by such certificate.  As soon as practicable
following the Distribution Date, separate certificates evidencing the Rights
("Right Certificates") will be mailed to holders of record of the Common Shares
as of the close of business on the Distribution Date and such separate Right
Certificates alone will evidence the Rights.

     The Rights are not exercisable until the Distribution Date.  The Rights
will expire on November 6, 2006 (the "Final Expiration Date"), unless the Final
Expiration Date is extended

                                       2.
<PAGE>
 
or unless the Rights are earlier redeemed or exchanged by the Company, in each
case, as described below.

     The Purchase Price payable, and the number of Preferred Shares or other
securities or property issuable, upon exercise of the Rights are subject to
adjustment from time to time to prevent dilution (i) in the event of a stock
dividend on, or a subdivision, combination or reclassification of, the Preferred
Shares, (ii) upon the grant to holders of the Preferred Shares of certain rights
or warrants to subscribe for or purchase Preferred Shares at a price, or
securities convertible into Preferred Shares with a conversion price, less than
the then-current market price of the Preferred Shares or (iii) upon the
distribution to holders of the Preferred Shares of evidences of indebtedness or
assets (excluding regular periodic cash dividends paid out of earnings or
retained earnings or dividends payable in Preferred Shares) or of subscription
rights or warrants (other than those referred to above).

     The number of outstanding Rights and the number of one one-hundredths of a
Preferred Share issuable upon exercise of each Right are also subject to
adjustment in the event of a stock split of the Common Shares or a stock
dividend on the Common Shares payable in Common Shares or subdivisions,
consolidations or combinations of the Common Shares occurring, in any such case,
prior to the Distribution Date.

     Preferred Shares purchasable upon exercise of the Rights will not be
redeemable.  Each Preferred Share will be entitled to a minimum preferential
quarterly dividend payment of $l per share but will be entitled to an aggregate
dividend of 100 times the dividend declared per Common Share.  In the event of
liquidation, the holders of the Preferred Shares will be entitled to a minimum
preferential liquidation payment of $100 per share but will be entitled to an
aggregate payment of 100 times the payment made per Common Share.  Each
Preferred Share will have 100 votes, voting together with the Common Shares.
Finally, in the event of any merger, consolidation or other transaction in which
Common Shares are exchanged, each Preferred Share will be entitled to receive
100 times the amount received per Common Share.  These rights are protected by
customary anti-dilution provisions.  Because of the nature of the Preferred
Shares' dividend, liquidation and voting rights, the value of the one one-
hundredth interest in a Preferred Share purchasable upon exercise of each Right
should approximate the value of one Common Share.  The Preferred Shares rank
junior to all other series of the Company's preferred stock.

     In the event that the Company is acquired by any person, other than Samuel
Wohlstadter, in a merger or other business combination transaction or 50% or
more of its consolidated assets or earning power are sold to any person other
than Samuel Wohlstadter, proper provision will be made so that each holder of a
Right will thereafter have the right to receive, upon the exercise thereof at
the then current exercise price of the Right, that number of shares of common
stock of the acquiring company which at the time of such transaction will have a
market value of two times the exercise price of the Right.  In the event that
any person or group of affiliated or associated persons becomes an Acquiring
Person, proper provision shall be made so that each holder of a Right, other
than Rights beneficially owned by the Acquiring Person (which will

                                       3.
<PAGE>
 
thereafter be void), will thereafter have the right to receive upon exercise
that number of Common Shares having a market value of two times the exercise
price of the Right.

     At any time after any Person becomes an Acquiring Person and prior to the
acquisition by such person or group of 50% or more of the outstanding Common
Shares, the Board of Directors of the Company may exchange the Rights (other
than Rights owned by such person or group which will have become void), in whole
or in part, at an exchange ratio of one Common Share, or one one-hundredth of a
Preferred Share (or of a share of a class or series of the Company's preferred
stock having equivalent rights, preferences and privileges), per Right (subject
to adjustment).

     With certain exceptions, no adjustment in the Purchase Price will be
required until cumulative adjustments require an adjustment of at least 1% in
such Purchase Price.  No fractional Preferred Shares will be issued (other than
fractions which are integral multiples of one one-hundredth of a Preferred
Share, which may, at the election of the Company, be evidenced by depositary
receipts) and in lieu thereof, an adjustment in cash will be made based on the
market price of the Preferred Shares on the last trading day prior to the date
of exercise.

     At any time prior to the earliest of (i) the time a person has become an
Acquiring Person, or (ii) the Final Expiration Date, the Board of Directors of
the Company may redeem the Rights in whole, but not in part, at a price of $.01
per Right (the "Redemption Price").  Following the expiration of the above
periods, the Rights become nonredeemable.  Immediately upon any redemption of
the Rights, the right to exercise the Rights will terminate and the only right
of the holders of Rights will be to receive the Redemption Price.

     The terms of the Rights may be amended by the Board of Directors of the
company without the consent of the holders of the Rights, including an amendment
to lower certain thresholds described above to any percentage which is (i)
greater than the largest percentage of the outstanding Common Shares then known
to the Company to be beneficially owned by any person or group of affiliated or
associated persons (other than an excepted person) and (ii) not less than 10%,
except that from and after such time as any person or group of affiliated or
associated persons becomes an Acquiring Person no such amendment may adversely
affect the interests of the holders of the Rights.

     Until a Right is exercised, the holder thereof, as such, will have no
rights as a stockholder of the Company, including, without limitation, the right
to vote or to receive dividends.

                                       4.
<PAGE>
 
Item 2.   Exhibits.
          -------- 

     Exhibit
     Number       Description
     ------       -----------
              
     1.1          Specimen Right Certificate.
                  
     2.1          Rights Agreement, dated as of November 6, 1996 between the
                  Registrant and The First National Bank of Boston

_______________________


                                  SIGNATURE
                                  ---------

     Pursuant to the requirements of Section 12 of the Securities Exchange Act
of 1934, the Registrant has caused this registration statement to be signed on
its behalf by the undersigned, thereunto duly authorized.


                                      IGEN International, Inc.
                                      (Registrant)


Date:  November 30, 1996      By: /s/ George V. Migausky
                                  -----------------------------------------
                                    George V. Migausky
                                    Vice President, Chief Financial Officer

                                       5.
<PAGE>
 
                              INDEX TO EXHIBITS
                              -----------------


                                                               Page number in
                                                               sequentially
                                                               numbered version
                                                               ----------------

1.1  Specimen Rights Certificate


2.1  Rights Agreement, dated as of
      November 6, 1996 between
      Registrant and The First National Bank of Boston


- --------------------------

<PAGE>
 
                                                                   EXHIBIT 1.1

                          FORM OF RIGHT CERTIFICATE


CERTIFICATE NO. R-                                                  _____ RIGHTS


     NOT EXERCISABLE AFTER NOVEMBER 6, 2006 OR EARLIER IF REDEMPTION 
     OR EXCHANGE OCCURS.  THE RIGHTS ARE SUBJECT TO REDEMPTION AT 
     $.01 PER RIGHT AND TO EXCHANGE ON THE TERMS SET FORTH IN THE 
     RIGHTS AGREEMENT.


                              RIGHT CERTIFICATE

                          IGEN INTERNATIONAL, INC.


     This certifies that ___________________ or registered assigns, is the
registered owner of the number of Rights set forth above, each of which entitles
the owner thereof, subject to the terms, provisions and conditions of the Rights
Agreement, dated as of November 6, 1996 (the "Rights Agreement"), between IGEN
International, Inc., a Delaware corporation (the "Company"), and The First
National Bank of Boston (the "Rights Agent"), to purchase from the Company at
any time after the Distribution Date (as such term is defined in the Rights
Agreement) and prior to 5:00 P.M., Pacific Standard Time, on November 6, 2006 at
the office of the Rights Agent designated for such purpose, or at the office of
its successor as Rights Agent, one one-hundredth of a fully paid non-assessable
share of Series A Junior Participating Preferred Stock, par value $.001 per
share (the "Preferred Shares"), of the Company, at a purchase price of $65.00
per one one-hundredth of a Preferred Share (the "Purchase Price"), upon
presentation and surrender of this Right Certificate with the Form of Election
to Purchase duly executed.  The number of Rights evidenced by this Right
Certificate (and the number of one one-hundredths of a Preferred Share which may
be purchased upon exercise hereof) set forth above, and the Purchase Price set
forth above, are the number and Purchase Price as of November 6, 1996 based on
the Preferred Shares as constituted at such date.

     From and after the time any Person becomes an Acquiring Person, (as such
terms are defined in the Rights Agreement), if the Rights evidenced by this
Right Certificate are beneficially owned by (i) an Acquiring Person or an
Affiliate or Associate of any such Acquiring Person (as such terms are defined
in the Rights Agreement), (ii) a transferee of any such Acquiring Person,
Associate or Affiliate who becomes a transferee after the Acquiring Person
becomes such, or (iii) under certain circumstances specified in the Rights
Agreement, a transferee of any such Acquiring Person, Associate or Affiliate who
becomes a transferee prior to or concurrently with the Acquiring Person becoming
such, such Rights shall become null and void and no holder hereof shall have any
right with respect to such Rights from and after the time any Person becomes an
Acquiring Person.

                                       1.
<PAGE>
 
     As provided in the Rights Agreement, the Purchase Price and the number of
one one-hundredths of a Preferred Share which may be purchased upon the exercise
of the Rights evidenced by this Right Certificate are subject to modification
and adjustment upon the happening of certain events.

     This Right Certificate is subject to all of the terms, provisions and
conditions of the Rights Agreement, as amended from time to time, which terms,
provisions and conditions are hereby incorporated herein by reference and made a
part hereof and to which Rights Agreement reference is hereby made for a full
description of the rights, limitations of rights, obligations, duties and
immunities hereunder of the Rights Agent, the Company and the holders of the
Right Certificates.  Copies of the Rights Agreement are on file at the principal
executive offices of the Company and the above-mentioned offices of the Rights
Agent.

     This Right Certificate, with or without other Right Certificates, upon
surrender at the office of the Rights Agent designated for such purpose, may be
exchanged for another Right Certificate or Right Certificates of like tenor and
date evidencing Rights entitling the holder to purchase a like aggregate number
of Preferred Shares as the Rights evidenced by the Right Certificate or Right
Certificates surrendered shall have entitled such holder to purchase.  If this
Right Certificate shall be exercised in part, the holder shall be entitled to
receive upon surrender hereof another Right Certificate or Right Certificates
for the number of whole Rights not exercised.

     Subject to the provisions of the Rights Agreement, the Rights evidenced by
this Certificate (i) may be redeemed by the Company at a redemption price of
$.01 per Right or (ii) may be exchanged in whole or in part for shares of the
Company's Common Stock or Preferred Shares, par value $.001 per share.

     No fractional Preferred Shares will be issued upon the exercise of any
Right or Rights evidenced hereby (other than fractions which are integral
multiples of one one-hundredth of a Preferred Share, which may, at the election
of the Company, be evidenced by depositary receipts) but in lieu thereof a cash
payment will be made, as provided in the Rights Agreement.

     No holder of this Right Certificate shall be entitled to vote or receive
dividends or be deemed for any purpose the holder of the Preferred Shares or of
any other securities of the Company which may at any time be issuable on the
exercise hereof, nor shall anything contained in the Rights Agreement or herein
be construed to confer upon the holder hereof, as such, any of the rights of a
stockholder of the Company or any right to vote for the election of directors or
upon any matter submitted to stockholders at any meeting thereof, or to give or
withhold consent to any corporate action, or to receive notice of meetings or
other actions affecting stockholders (except as provided in the Rights
Agreement), or to receive dividends or subscription rights, or otherwise, until
the Right or Rights evidenced by this Right Certificate shall have been
exercised as provided in the Rights Agreement.

     This Right Certificate shall not be valid or obligatory for any purpose
until it shall have been countersigned by the Rights Agent.

                                       2.
<PAGE>
 
     WITNESS the facsimile signature of the proper officers of the Company and
its corporate seal.  Dated as of __________.


ATTEST:                                  IGEN INTERNATIONAL, INC.



______________________________           ________________________________ 
Andrei M. Manoliu                        Richard J. Massey, Ph.D.
Secretary                                President and Chief Operating Officer


COUNTERSIGNED:


THE FIRST NATIONAL BANK OF BOSTON
as Rights Agent



By: ___________________________
     Authorized Signature

                                       3.
<PAGE>
 
                  Form of Reverse Side of Right Certificate


                             FORM OF ASSIGNMENT


              (To be executed by the registered holder if such
             holder desires to transfer the Right Certificate.)


     FOR VALUE RECEIVED ______________________________________ hereby sells,
assigns and transfers unto

       ______________________________________________________________
                (Please print name and address of transferee)

______________________________________________________________ this Right

Certificate, together with all right, title and interest therein, and does
hereby irrevocably constitute and appoint ________________________ Attorney, to
transfer the within Right Certificate on the books of the within-named Company,
with full power of substitution.


Dated:  ____________________



                              ________________________________
                              Signature



           Form of Reverse Side of Right Certificate -- continued

                                       4.
<PAGE>
 
Signature Guaranteed:

     Signatures must be guaranteed by an "eligible guarantor institution" as
defined in Rule 17Ad-15 promulgated under the Securities Exchange Act of 1934,
as amended.

- ---------------------------------------------------------------

     The undersigned hereby certifies that (1) the Rights evidenced by this
Right Certificate are not being sold, assigned or transferred by or on behalf of
a Person who is or was an Acquiring Person, an Interested Stockholder or an
Affiliate or Associate thereof (as defined in the Rights Agreement); and (2)
after due inquiry and to the best of the knowledge of the  undersigned, the
undersigned did not acquire the Rights evidenced by this Right Certificate from
any Person who is or was an Acquiring Person, an Interested Stockholder, or an
Affiliate or Associate thereof (as such terms are defined in the Rights
Agreement).


                              ________________________________
                              Signature

                                       5.
<PAGE>
 
                        FORM OF ELECTION TO PURCHASE

                (To be executed if holder desires to exercise
                Rights represented by the Right Certificate.)


To IGEN International, Inc.

     The undersigned hereby irrevocably elects to exercise __________________
Rights represented by this Right Certificate to purchase the Preferred Shares
issuable upon the exercise of such Rights and requests that certificates for
such Preferred Shares be issued in the name of:

Please insert social security
or other identifying number: ______________

______________________________________________________________
                        (Please print name and address)

______________________________________________________________

If such number of Rights shall not be all the Rights evidenced by this Right
Certificate, a new Right Certificate for the balance remaining of such Rights
shall be registered in the name of and delivered to:

Please insert social security
or other identifying number: ______________


______________________________________________________________
                        (Please print name and address)

______________________________________________________________

Dated:  _________________


                              ________________________________
                              Signature



           Form of Reverse Side of Right Certificate -- continued

                                       6.
<PAGE>
 
Signature Guaranteed:

     Signatures must be guaranteed by an "eligible guarantor institution" as
defined in Rule 17Ad-15 promulgated under the Securities Exchange Act of 1934,
as amended.


- ---------------------------------------------------------------

     The undersigned hereby certifies that the Rights evidenced by this Right
Certificate are not being beneficially owned by nor are they being exercised on
behalf of (1) an Acquiring Person, an Interested Stockholder or an Affiliate or
Associate thereof (as defined in the Rights Agreement); and (2) after due
inquiry and to the best of the knowledge of the undersigned, the undersigned did
not acquire the Rights evidenced by this Right Certificate from any Person who
is or was an Acquiring Person, an Interested Stockholder, or an Affiliate or
Associate thereof (as such terms are defined in the Rights Agreement).



                              ________________________________
                              Signature


- -----------------------------------------------


                                   NOTICE

     The signature in the Form of Assignment or Form of Election to Purchase, as
the case may be, must conform to the name as written upon the face of this Right
Certificate in every particular, without alteration or enlargement or any change
whatsoever.

     In the event the certification set forth above in the Form of Assignment or
the Form of Election to Purchase, as the case may be, is not completed, the
Company and the Rights Agent will deem the beneficial owner of the Rights
evidenced by this Right Certificate to be an Acquiring Person or an Affiliate or
Associate thereof (as defined in the Rights Agreement) and such Assignment or
Election to Purchase will not be honored.

                                       7.

<PAGE>
 
                                                                   EXHIBIT 2.1

         ___________________________________________________________

                          IGEN INTERNATIONAL, INC.

                                     AND

                      THE FIRST NATIONAL BANK OF BOSTON
                               AS RIGHTS AGENT

                              RIGHTS AGREEMENT

                        DATED AS OF NOVEMBER 6, 1996

         ___________________________________________________________
<PAGE>
 
                              RIGHTS AGREEMENT


          AGREEMENT, dated as of November 6, 1996, between IGEN INTERNATIONAL,
INC., a Delaware corporation (the "Company"), and THE FIRST NATIONAL BANK OF
BOSTON ("Rights Agent").

          The Board of Directors of the Company has authorized and declared a
dividend of one preferred share purchase right (a "Right") for each Common Share
(as hereinafter defined) of the Company outstanding at the close of business on
November 6, 1996 (the "Record Date "), each Right representing the right to
purchase one one-hundredth of a Preferred Share (as hereinafter defined), upon
the terms and subject to the conditions herein set forth, and has further
authorized and directed the issuance of one Right with respect to each Common
Share that shall become outstanding between the Record Date and the earliest of
the Distribution Date, the Redemption Date and the Final Expiration Date (as
such terms are hereinafter defined); provided, however, that Rights may be
issued with respect to Common Shares that shall become outstanding after the
Distribution Date and prior to the earlier of the Redemption Date and the Final
Expiration Date in accordance with the provisions of Section 22 of this
Agreement.

          Accordingly, in consideration of the premises and the mutual
agreements herein set forth, the parties hereby agree as follows:

     SECTION 1.  CERTAIN DEFINITIONS. For purposes of this Agreement, the
following terms have the meanings indicated:

     (a) "ACQUIRING PERSON" shall mean any Person (as such term is hereinafter
defined) who or which, together with all Affiliates and Associates (as such
terms are hereinafter defined) of such Person, shall be the Beneficial Owner
(as such term is hereinafter defined) of 15% or more of the Common Shares of
the Company then outstanding, but shall not include any Excluded Person (as
such term is hereinafter defined). Notwithstanding the foregoing, no Person
shall become an "Acquiring Person" either (x) as the result of an acquisition
of Common Shares by the Company which, by reducing the number of shares
outstanding, increases the proportionate number of shares beneficially owned
by such Person to 15% or more of the Common Shares of the Company then
outstanding; provided, however, that if a Person shall become the Beneficial
Owner of 15% or more of the Common Shares of the Company then outstanding by
reason of share purchases by the Company and shall, after such share purchases
by the Company, become the Beneficial Owner of any additional Common Shares of
the Company, then such Person shall be deemed to be an "Acquiring Person" or
(y) if the Incumbent Board (as such term is hereinafter defined) determines in
good faith that a Person who would otherwise be an "Acquiring Person," as
defined pursuant to the foregoing provisions of this paragraph (a), has become
such inadvertently, and such Person divests as promptly as practicable a
sufficient number of Common Shares so that such Person would no longer be an
Acquiring Person, as defined pursuant to the foregoing provisions of this
paragraph (a), then such Person shall not be deemed to be an "Acquiring
Person" for any purposes of this Agreement.
<PAGE>
 
     (b) "AFFILIATE" and "ASSOCIATE" shall have the respective meanings
ascribed to such terms in Rule 12b-2 of the General Rules and Regulations
under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), as
in effect on the date of this Agreement; provided, however, that the limited
                                         --------  -------
partners of a limited partnership shall not be deemed to be Associates of such
limited partnership solely by virtue of their limited partnership interest.

     (c) A Person shall be deemed the "BENEFICIAL OWNER" of and shall be
deemed to "beneficially own" any securities:

         (i)   which such Person or any of such Person's Affiliates or
     Associates beneficially owns, directly or indirectly;

         (ii)  which such Person or any of such Person's Affiliates or
     Associates has (A) the right to acquire (whether such right is
     exercisable immediately or only after the passage of time) pursuant to
     any agreement, arrangement or understanding (other than customary
     agreements with and between underwriters and selling group members with
     respect to a bona fide public offering of securities), or upon the
     exercise of conversion rights, exchange rights, rights (other than these
     Rights), warrants or options, or otherwise; provided, however, that a
                                                 --------  -------
     Person shall not be deemed the Beneficial Owner of, or to beneficially
     own, securities tendered pursuant to a tender or exchange offer made by
     or on behalf of such Person or any of such Person's Affiliates or
     Associates until such tendered securities are accepted for purchase or
     exchange; or (B) the right to vote pursuant to any agreement, arrangement
     or understanding; provided, however, that a Person shall not be deemed
                       --------  -------
     the Beneficial Owner of, or to beneficially own, any security if the
     agreement, arrangement or understanding to vote such security (1) arises
     solely from a revocable proxy or consent given to such Person in response
     to a public proxy or consent solicitation made pursuant to, and in
     accordance with, the applicable rules and regulations promulgated under
     the Exchange Act and (2) is not also then reportable on Schedule 13D
     under the Exchange Act (or any comparable or successor report); or

         (iii) which are beneficially owned, directly or indirectly, by any
     other Person with which such Person or any of such Person's Affiliates or
     Associates has any agreement, arrangement or understanding (other than
     customary agreements with and between underwriters and selling group
     members with respect to a bona fide public offering of securities) for
     the purpose of acquiring, holding, voting (except to the extent
     contemplated by the proviso to Section 1(c)(ii)(B)) or disposing of any
     securities of the Company.
 
Notwithstanding anything in this definition of Beneficial Ownership to the
contrary, the phrase, "then outstanding," when used with reference to a Person's
Beneficial Ownership of securities of the Company, shall mean the number of such
securities then issued and outstanding together with the number of such
securities not then actually issued and outstanding which such Person would be
deemed to own beneficially hereunder.
<PAGE>
 
     (d) "BUSINESS DAY" shall mean any day other than a Saturday, a Sunday, or
a day on which banking institutions in the State of Maryland are authorized or
obligated by law or executive order to close.

     (e) "CHANGE OF CONTROL" shall mean:

         (i)   The acquisition (other than from the Company) by any person,
     entity or "group," within the meaning of Section 13(d)(3) or 14(d)(2) of
     the Exchange Act, (other than any Excluded Person) of beneficial
     ownership, (within the meaning of Rule 13d-3 promulgated under the
     Exchange Act) of 50% or more of either the then outstanding Common Shares
     or the combined voting power of the Company's then outstanding voting
     securities entitled to vote generally in the election of directors; or

         (ii)  Individuals who, as of the date hereof, constitute the Board
     (as of the date hereof the "Incumbent Board") cease for any reason to
     constitute at least a majority of the Board, provided, however, that any
                                                  --------  -------
     person becoming a director subsequent to the date hereof whose election,
     or nomination for election by the Company's stockholders, was approved by
     a vote of at least a majority of the directors then comprising the
     Incumbent Board (other than an Affiliate or Associate of an Acquiring
     Person) shall be, for purposes of this Agreement, considered as though
     such person were a member of the Incumbent Board; or

         (iii) Approval by the stockholders of the Company of a
     reorganization, merger, or consolidation, in each case, with respect to
     which persons who were the stockholders of the Company immediately prior
     to such reorganization, merger or consolidation do not immediately
     thereafter, own more than 50% of the combined voting power entitled to
     vote generally in the election of directors of the reorganized, merged or
     consolidated company's then outstanding voting securities, or a
     liquidation or dissolution of the Company or of the sale of all or
     substantially all of the assets of the Company.

     (f) "CLOSE OF BUSINESS" on any given date shall mean 5:00 p.m., New York
time, on such date; provided, however, that if such date is not a Business Day
                    --------  -------
it shall mean 5:00 p.m., New York time, on the next succeeding Business Day.

     (g) "COMMON SHARES" when used with reference to the Company shall mean
the shares of common stock, par value $.001 per share, of the Company. "Common
Shares" when used with reference to any Person other than the Company shall
mean the capital stock (or equity interest) with the greatest voting power of
such other Person or, if such other Person is a Subsidiary of another Person,
the Person or Persons which ultimately control such first-mentioned Person.

     (h) "DISTRIBUTION DATE" shall have the meaning set forth in Section 3
hereof.

     (i) "EXCLUDED PERSON" shall mean (i) the Company, (ii) any Subsidiary (as
such term is hereinafter defined) of the Company, (iii) any employee benefit
plan of the Company or any Subsidiary of the Company, (iv) any entity holding
Common Shares for or pursuant to the terms
<PAGE>
 
of any such plan or (v) Mr. Samuel J. Wohlstadter, his Affiliates or Associates,
his heirs, and any trust or foundation to which he has transferred or may
transfer Common Shares of the Company ("Wohlstadter").

     (j) "FINAL EXPIRATION DATE" shall have the meaning set forth in Section 7
hereof.

     (k) "INTERESTED STOCKHOLDER" shall mean any Acquiring Person or any
Affiliate or Associate of an Acquiring Person or any other Person in which any
such Acquiring Person, Affiliate or Associate has an interest, or any other
Person acting directly or indirectly on behalf of or in concert with any such
Acquiring Person, Affiliate or Associate.

     (l) "PERSON" shall mean any individual, firm, corporation or other
entity, and shall include any successor (by merger or otherwise) of such
entity.

     (m) "PREFERRED SHARES" shall mean shares of Series A Junior Participating
Preferred Stock, par value $.001 per share, of the Company having the
designations and the powers, preferences and rights, and the qualifications,
limitations and restrictions set forth in the Form of Certificate of
Designation attached to this Agreement as Exhibit A.

     (n) "REDEMPTION DATE" shall have the meaning set forth in Section 7
hereof.

     (o) "SHARES ACQUISITION DATE" shall mean the first date of public
announcement by the Company or an Acquiring Person that an Acquiring Person
has become such provided, however that, if such Person is determined not to
                --------  -------
have become an Acquiring Person pursuant to (y) of the last sentence of
Section 1(a) hereof, then no Shares Acquisition Date shall be deemed to have
occurred.

     (p) "SUBSIDIARY" of any Person shall mean any corporation or other entity
of which a majority of the voting power of the voting equity securities or
equity interest is owned, directly or indirectly, by such Person.

     (q) "TRANSACTION" shall mean any merger, consolidation or sale of assets
described in Section 13(a) hereof or any acquisition of shares of Common Stock
of the Company which would result in a Person becoming a Transaction Person.

     (r) "TRANSACTION PERSON" with respect to a Transaction shall mean (x) any
Person who (i) is or will become an Acquiring Person or a Principal Party (as
such term is defined in Section 13(b) hereof) if the Transaction were to be
consummated and (ii) directly or indirectly proposed or nominated a director
of the Company which director is in office at the time of consideration of the
Transaction, or (y) an Affiliate or Associate of such a Person.

     SECTION 2.  APPOINTMENT OF RIGHTS AGENT.  The Company hereby appoints the
Rights Agent to act as agent for the Company and the holders of the Rights (who,
in accordance with Section 3 hereof, shall prior to the Distribution Date also
be the holders of the Common Shares) in accordance with the terms and conditions
hereof, and the Rights Agent hereby accepts such
<PAGE>
 
appointment.  The Company may from time to time appoint such co-Rights Agents as
it may deem necessary or desirable.

     SECTION 3.  ISSUE OF RIGHT CERTIFICATES.

     (a) Until the earlier of (i) the Shares Acquisition Date or (ii) the tenth
business day (or such later date as may be determined by action of the Board of
Directors prior to such time as any Person becomes an Acquiring Person) after
the date of the commencement (determined in accordance with Rule 14d-2 under the
Exchange Act) by any Person (other than any Excluded Person) of, or of the first
public announcement of the intention of any Person (other than any Excluded
Person) to commence, a tender or exchange offer (which intention to commence
remains in effect for five Business Days after such announcement), the
consummation of which would result in any Person becoming an Acquiring Person
(including any such date which is after the date of this Agreement and prior to
the issuance of the Rights, the earlier of such dates being herein referred to
as the "Distribution Date"), (x) the Rights will be evidenced by the
certificates for Common Shares registered in the names of the holders thereof
(which certificates shall also be deemed to be Right Certificates) and not by
separate Right Certificates, and (y) the Rights (and the right to receive Right
Certificates therefor) will be transferable only in connection with the transfer
of Common Shares.  As soon as practicable after the Distribution Date, the
Company will prepare and execute, the Rights Agent will countersign, and the
Company will send or cause to be sent (and the Rights Agent will, if requested,
send) by first-class, insured, postage-prepaid mail, to each record holder of
Common Shares as of the close of business on the Distribution Date, at the
address of such holder shown on the records of the Company, a Right Certificate,
in substantially the form of Exhibit B hereto (a "Right Certificate"),
evidencing one Right for each Common Share so held.  As of the Distribution
Date, the Rights will be evidenced solely by such Right Certificates.

     (b) On the Record Date, or as soon as practicable thereafter, the Company
will send a copy of a Summary of Rights to Purchase Preferred Shares, in
substantially the form of Exhibit C hereto (the "Summary of Rights"), by first-
class, postage-prepaid mail, to each record holder of Common Shares as of the
close of business on the Record Date, at the address of such holder shown on the
records of the Company.  With respect to certificates for Common Shares
outstanding as of the Record Date, until the Distribution Date, the Rights will
be evidenced by such certificates registered in the names of the holders
thereof.  Until the Distribution Date (or the earlier of the Redemption Date and
the Final Expiration Date), the surrender for transfer of any certificate for
Common Shares outstanding on the Record Date shall also constitute the transfer
of the Rights associated with the Common Shares represented thereby.

     (c) Certificates for Common Shares which become outstanding (including,
without limitation, reacquired Common Shares referred to in the last sentence of
this paragraph (c)) after the Record Date but prior to the earliest of the
Distribution Date, the Redemption Date or the Final Expiration Date shall have
impressed on, printed on, written on or otherwise affixed to them the following
legend:

          This certificate also evidences and entitles the holder 
          hereof to certain rights as set forth in a Rights Agreement 
          between IGEN
<PAGE>
 
          International, Inc. and THE FIRST NATIONAL BANK OF BOSTON, 
          dated as of November 6, 1996, as amended from time to time 
          (the "Rights Agreement"), the terms of which are hereby 
          incorporated herein by reference and a copy of which is on 
          file at the principal executive offices of IGEN International, 
          Inc.  Under certain circumstances, as set forth in the Rights 
          Agreement, such Rights will be evidenced by separate 
          certificates and will no longer be evidenced by this 
          certificate.  IGEN International, Inc. will mail to the holder 
          of this certificate a copy of the Rights Agreement without 
          charge after receipt of a written request therefor.  As 
          described in the Rights Agreement, Rights issued to any Person 
          who becomes an Acquiring Person or an Affiliate or Associate 
          thereof (as defined in the Rights Agreement) and certain 
          related persons, whether currently held by or on behalf of 
          such Person or by any subsequent holder shall become null
          and void.

With respect to such certificates containing the foregoing legend, until the
Distribution Date, the Rights associated with the Common Shares represented by
such certificates shall be evidenced by such certificates alone, and the
surrender for transfer of any such certificate shall also constitute the
transfer of the Rights associated with the Common Shares represented thereby.
In the event that the Company purchases or acquires any Common Shares after the
Record Date but prior to the Distribution Date, any Rights associated with such
Common Shares shall be deemed canceled and retired so that the Company shall not
be entitled to exercise any Rights associated with the Common Shares which are
no longer outstanding.

     SECTION 4.  FORM OF RIGHT CERTIFICATES.

     (a) The Right Certificates (and the form of election to purchase Preferred
Shares, the form of assignment and the form of certification to be printed on
the reverse thereof) shall be substantially the same as Exhibit B hereto and may
have such marks of identification or designation and such legends, summaries or
endorsements printed thereon as the Company may deem appropriate and as are not
inconsistent with the provisions of this Agreement, or as may be required to
comply with any applicable law or with any rule or regulation made pursuant
thereto or with any rule or regulation of any stock exchange on which the Rights
may from time to time be listed, or to conform to usage.  Subject to the
provisions of Section 22 hereof, the Right Certificates shall entitle the
holders thereof to purchase such number of one one-hundredths of a Preferred
Share as shall be set forth therein at the price per one one-hundredth of a
Preferred Share set forth therein (the "Purchase Price"), but the number of such
one one-hundredths of a Preferred Share and the Purchase Price shall be subject
to adjustment as provided herein.

     (b) Any Right Certificate issued pursuant to Section 3(a) or Section 22
hereof that represents Rights which are null and void pursuant to Section
11(a)(ii) of this Agreement and any Right Certificate issued pursuant to Section
6 or Section 11 hereof upon transfer, exchange, replacement or adjustment of any
other Right Certificate referred to in this sentence, shall contain (to the
extent feasible) the following legend:
<PAGE>
 
          The Rights represented by this Right Certificate are or 
          were beneficially owned by a Person who was or became an 
          Acquiring Person or an Affiliate or Associate of an 
          Acquiring Person (as such terms are defined in the Rights 
          Agreement). Accordingly, this Right Certificate and the 
          Rights represented hereby are null and void.

The provisions of Section 11(a)(ii) of this Rights Agreement shall be operative
whether or not the foregoing legend is contained on any such Right Certificate.

     SECTION 5.  COUNTERSIGNATURE AND REGISTRATION.  The Right Certificates
shall be executed on behalf of the Company by its Chairman of the Board, its
Chief Executive Officer, its President, its Vice Chairman of the Board, its
Chief Financial Officer, or any of its Vice Presidents, either manually or by
facsimile signature, shall have affixed thereto the Company's seal or a
facsimile thereof, and shall be attested by the Secretary or an Assistant
Secretary of the Company, either manually or by facsimile signature.  The Right
Certificates shall be manually countersigned by the Rights Agent and shall not
be valid for any purpose unless countersigned.  In case any officer of the
Company who shall have signed any of the Right Certificates shall cease to be
such officer of the Company before countersignature by the Rights Agent and
issuance and delivery by the Company, such Right Certificates, nevertheless, may
be countersigned by the Rights Agent and issued and delivered by the Company
with the same force and effect as though the person who signed such Right
Certificates had not ceased to be such officer of the Company; and any Right
Certificate may be signed on behalf of the Company by any person who, at the
actual date of the execution of such Right Certificate, shall be a proper
officer of the Company to sign such Right Certificate, although at the date of
the execution of this Rights Agreement any such person was not such an officer.

     Following the Distribution Date, the Rights Agent will keep or cause to be
kept, at its office designated for such purpose, books for registration and
transfer of the Right Certificates issued hereunder.  Such books shall show the
names and addresses of the respective holders of the Right Certificates, the
number of Rights evidenced on its face by each of the Right Certificates and the
date of each of the Right Certificates.

     SECTION 6.  TRANSFER, SPLIT UP, COMBINATION AND EXCHANGE OF RIGHT
CERTIFICATES; MUTILATED, DESTROYED, LOST OR STOLEN RIGHT CERTIFICATES.  Subject
to the provisions of Section 4(b), Section 11(a)(ii), Section 14 and Section 24
hereof, at any time after the close of business on the Distribution Date, and at
or prior to the close of business on the earlier of the Redemption Date or the
Final Expiration Date, any Right Certificate or Right Certificates may be
transferred, split up, combined or exchanged for another Right Certificate or
Right Certificates, entitling the registered holder to purchase a like number of
one one-hundredths of a Preferred Share as the Right Certificate or Right
Certificates surrendered then entitled such holder to purchase.  Any registered
holder desiring to transfer, split up, combine or exchange any Right Certificate
or Right Certificates shall make such request in writing delivered to the Rights
Agent, and shall surrender the Right Certificate or Right Certificates to be
transferred, split up, combined or exchanged at the office of the Rights Agent
designated for such purpose.  Neither the Rights Agent nor the Company shall be
obligated to take any action whatsoever with
<PAGE>
 
respect to the transfer of any such surrendered Right Certificate until the
registered holder shall have completed and signed the certificate contained in
the form of assignment on the reverse side of such Right Certificate and shall
have provided such additional evidence of the identity of the Beneficial Owner
(or former Beneficial Owner) or Affiliates or Associates thereof as the Company
shall reasonably request.  Thereupon the Rights Agent shall, subject to Section
4(b), Section 11(a)(ii), Section 14 and Section 24 hereof, countersign and
deliver to the person entitled thereto a Right Certificate or Right
Certificates, as the case may be, as so requested.  The Company may require
payment of a sum sufficient to cover any tax or governmental charge that may be
imposed in connection with any transfer, split up, combination or exchange of
Right Certificates.

     Upon receipt by the Company and the Rights Agent of evidence reasonably
satisfactory to them of the loss, theft, destruction or mutilation of a Right
Certificate, and, in case of loss, theft or destruction, of indemnity or
security reasonably satisfactory to them, and, at the Company's request,
reimbursement to the Company and the Rights Agent of all reasonable expenses
incidental thereto, and upon surrender to the Rights Agent and cancellation of
the Right Certificate if mutilated, the Company will issue, execute and deliver
a new Right Certificate of like tenor to the Rights Agent for countersignature
and delivery to the registered holder in lieu of the Right Certificate so lost,
stolen, destroyed or mutilated.

     SECTION 7.  EXERCISE OF RIGHTS; PURCHASE PRICE; EXPIRATION DATE OF RIGHTS.

     (a) The registered holder of any Right Certificate may exercise the Rights
evidenced thereby (except as otherwise provided herein) in whole or in part at
any time after the Distribution Date upon surrender of the Right Certificate,
with the form of election to purchase on the reverse side thereof duly executed,
to the Rights Agent at the office of the Rights Agent designated for such
purpose, together with payment of the Purchase Price for each one one-hundredth
of a Preferred Share (or such other number of shares or other securities) as to
which the Rights are exercised, at or prior to the earliest of (i) the close of
business on November 6, 2006 (the "Final Expiration Date"), (ii) the time at
which the Rights are redeemed as provided in Section 23 hereof (the "Redemption
Date"), or (iii) the time at which such Rights are exchanged as provided in
Section 24 hereof.

     (b) The Purchase Price for each one one-hundredth of a Preferred Share
pursuant to the exercise of a Right shall initially be $65, shall be subject to
adjustment from time to time as provided in Sections 11 and 13 hereof and shall
be payable in lawful money of the United States of America in accordance with
paragraph (c) below.

     (c) Upon receipt of a Right Certificate representing exercisable Rights,
with the form of election to purchase duly executed, accompanied by payment of
the Purchase Price for the shares to be purchased and an amount equal to any
applicable transfer tax required to be paid by the holder of such Right
Certificate in accordance with Section 9 hereof by certified check, cashier's
check, bank draft or money order payable to the order of the Company, the Rights
Agent shall thereupon promptly (i) (A) requisition from any transfer agent for
the Preferred Shares certificates for the number of Preferred Shares to be
purchased and the Company hereby irrevocably authorizes its transfer agent to
comply with all such requests, or (B) if the Company,
<PAGE>
 
in its sole discretion, shall have elected to deposit the Preferred Shares
issuable upon exercise of the Rights hereunder into a depository, requisition
from the depositary agent depositary receipts representing such number of one
one-hundredths of a Preferred Share as are to be purchased (in which case
certificates for the Preferred Shares represented by such receipts shall be
deposited by the transfer agent with the depositary agent) and the Company
hereby directs the depositary agent to comply with such request, (ii) when
appropriate, requisition from the Company the amount of cash to be paid in lieu
of issuance of fractional shares in accordance with Section 14 hereof, (iii)
after receipt of such certificates or depositary receipts, cause the same to be
delivered to or upon the order of the registered holder of such Right
Certificate, registered in such name or names as may be designated by such
holder and (iv) when appropriate, after receipt, deliver such cash to or upon
the order of the registered holder of such Right Certificate.  In the event that
the Company is obligated to issue securities of the Company other than Preferred
Shares (including Common Shares) of the Company pursuant to Section 11(a)
hereof, the Company will make all arrangements necessary so that such other
securities are available for distribution by the Rights Agent, if and when
appropriate.

     In addition, in the case of an exercise of the Rights by a holder pursuant
to Section 11(a)(ii), the Rights Agent shall return such Right Certificate to
the registered holder thereof after imprinting, stamping or otherwise indicating
thereon that the rights represented by such Right Certificate no longer include
the rights provided by Section 11(a)(ii) of the Rights Agreement, and, if fewer
than all the Rights represented by such Right Certificate were so exercised, the
Rights Agent shall indicate on the Right Certificate the number of Rights
represented thereby which continue to include the rights provided by Section
11(a)(ii).

     (d) In case the registered holder of any Right Certificate shall exercise
fewer than all the Rights evidenced thereby, a new Right Certificate evidencing
Rights equivalent to the Rights remaining unexercised shall be issued by the
Rights Agent to the registered holder of such Right Certificate or to his duly
authorized assigns, subject to the provisions of Section 14 hereof.

     (e) The Company covenants and agrees that it will cause to be reserved and
kept available out of its authorized and unissued Preferred Shares or any
Preferred Shares held in its treasury, the number of Preferred Shares that will
be sufficient to permit the exercise in full of all outstanding Rights in
accordance with this Section 7.

     (f) Notwithstanding anything in this Agreement to the contrary, neither the
Rights Agent nor the Company shall be obligated to undertake any action with
respect to a registered holder upon the occurrence of any purported exercise as
set forth in this Section 7 unless such registered holder shall have (i)
completed and signed the certification following the form of election to
purchase set forth on the reverse side of the Rights Certificate surrendered for
such exercise and (ii) provided such additional evidence of the identity of the
Beneficial Owner (or former Beneficial Owner) or Affiliates or Associates
thereof as the Company shall reasonably request.

     SECTION 8.  CANCELLATION AND DESTRUCTION OF RIGHT CERTIFICATES.  All Right
Certificates surrendered for the purpose of exercise, transfer, split up,
combination or exchange shall, if surrendered to the Company or to any of its
agents, be delivered to the Rights Agent for
<PAGE>
 
cancellation or in canceled form, or, if delivered or surrendered to the Rights
Agent, shall be canceled by it, and no Right Certificates shall be issued in
lieu thereof except as expressly permitted by any of the provisions of this
Rights Agreement.  The Company shall deliver to the Rights Agent for
cancellation and retirement, and the Rights Agent shall so cancel and retire,
any other Right Certificate purchased or acquired by the Company otherwise than
upon the exercise thereof.  The Rights Agent shall deliver all canceled Right
Certificates to the Company, or shall, at the written request of the Company,
destroy such canceled Right Certificates, and in such case shall deliver a
certificate of destruction thereof to the Company.

     SECTION 9.  AVAILABILITY OF PREFERRED SHARES.  The Company covenants and
agrees that so long as the Preferred Shares (and, after the time a person
becomes an Acquiring Person, Common Shares or any other securities) issuable
upon the exercise of the Rights may be listed on any national securities
exchange or quotation system, the Company shall use its best efforts to cause,
from and after such time as the Rights become exercisable, all shares reserved
for such issuance to be listed on such exchange or quotation system upon
official notice of issuance upon such exercise.

     The Company covenants and agrees that it will take all such action as may
be necessary to ensure that all Preferred Shares (or Common Shares and other
securities, as the case may be) delivered upon exercise of Rights shall, at the
time of delivery of the certificates for such Preferred Shares (subject to
payment of the Purchase Price), be duly and validly authorized and issued and
fully paid and nonassessable shares or other securities.

     The Company further covenants and agrees that it will pay when due and
payable any and all federal and state transfer taxes and charges which may be
payable in respect of the issuance or delivery of the Right Certificates or of
any Preferred Shares upon the exercise of Rights.  The Company shall not,
however, be required to pay any transfer tax which may be payable in respect of
any transfer or delivery of Right Certificates to a person other than, or the
issuance or delivery of certificates or depositary receipts for the Preferred
Shares in a name other than that of, the registered holder of the Right
Certificate evidencing Rights surrendered for exercise or to issue or to deliver
any certificates or depositary receipts for Preferred Shares upon the exercise
of any Rights until any such tax shall have been paid (any such tax being
payable by the holder of such Right Certificate at the time of surrender) or
until it has been established to the Company's reasonable satisfaction that no
such tax is due.

     As soon as practicable after the Shares Acquisition Date, the Company shall
use its best efforts to:

          (i)   prepare and file a registration statement under the Securities
     Act of 1933, as amended (the "Act"), with respect to the Rights and the
     securities purchasable upon exercise of the Rights on an appropriate
     form, will use its best efforts to cause such registration statement to
     become effective as soon as practicable after such filing and will use
     its best efforts to cause such registration statement to remain effective
     (with a prospectus at all times meeting the requirements of the Act)
     until the Final Expiration Date; and
<PAGE>
 
          (ii)  use its best efforts to qualify or register the Rights and the
     securities purchasable upon exercise of the Rights under the blue sky laws
     of such jurisdictions as may be necessary or appropriate.

     SECTION 10.  PREFERRED SHARES RECORD DATE.  Each person in whose name any
certificate for Preferred Shares or other securities is issued upon the exercise
of Rights shall for all purposes be deemed to have become the holder of record
of the Preferred Shares or other securities represented thereby on, and such
certificate shall be dated, the date upon which the Right Certificate evidencing
such Rights was duly surrendered with the forms of election and certification
duly executed and payment of the Purchase Price (and any applicable transfer
taxes) was made; provided, however, that if the date of such surrender and
                 --------  -------
payment is a date upon which the Preferred Shares or other securities transfer
books of the Company are closed, such person shall be deemed to have become the
record holder of such shares on, and such certificate shall be dated, the next
succeeding Business Day on which the Preferred Shares or other securities
transfer books of the Company are open.  Prior to the exercise of the Rights
evidenced thereby, the holder of a Right Certificate, as such, shall not be
entitled to any rights of a holder of Preferred Shares for which the Rights
shall be exercisable, including, without limitation, the right to vote, to
receive dividends or other distributions or to exercise any preemptive rights,
and shall not be entitled to receive any notice of any proceedings of the
Company, except as provided herein.

     SECTION 11.  ADJUSTMENT OF PURCHASE PRICE, NUMBER OF SHARES OR NUMBER OF
RIGHTS.  The Purchase Price, the number of Preferred Shares covered by each
Right and the number of Rights outstanding are subject to adjustment from time
to time as provided in this Section 11.

     (a)  (i)   In the event the Company shall at any time after the date of
this Agreement (A) declare a dividend on the Preferred Shares payable in
Preferred Shares, (B) subdivide the outstanding Preferred Shares, (C) combine
the outstanding Preferred Shares into a smaller number of Preferred Shares or
(D) issue any shares of its capital stock in a reclassification of the
Preferred Shares (including any such reclassification in connection with a
consolidation or merger in which the Company is the continuing or surviving
corporation), except as otherwise provided in this Section 11(a), the Purchase
Price in effect at the time of the record date for such dividend or of the
effective date of such subdivision, combination or reclassification, and the
number and kind of shares of capital stock issuable on such date, shall be
proportionately adjusted so that the holder of any Right exercised after such
time shall be entitled to receive the aggregate number and kind of shares of
capital stock which, if such Right had been exercised immediately prior to
such date and at a time when the Preferred Shares transfer books of the
Company were open, such holder would have owned upon such exercise and been
entitled to receive by virtue of such dividend, subdivision, combination or
reclassification; provided, however, that in no event shall the consideration
                  --------  -------
to be paid upon the exercise of one Right be less than the aggregate par value
of the shares of capital stock of the Company issuable upon exercise of one
Right. If an event occurs which would require an adjustment under both Section
11(a)(i) and Section 11(a)(ii), the adjustment provided for in this Section
11(a)(i) shall be in addition to, and shall be made prior to any adjustment
required pursuant to Section 11(a)(ii).
<PAGE>
 
          (ii)  Subject to Section 24 of this Agreement, in the event any Person
shall become an Acquiring Person, each holder of a Right shall, for a period of
180 days after the later of such time any Person becomes an Acquiring Person or
the effective date of an appropriate registration statement under the Act
pursuant to Section 9 hereof (provided, however that, if at any time prior to
                              --------  -------
the expiration or termination of the Rights there shall be a temporary
restraining order, a preliminary injunction, an injunction, or temporary
suspension by the Board of Directors, or similar obstacle to exercise of the
Rights (the "Injunction") which prevents exercise of the Rights, a new 180-day
period shall commence on the date the Injunction is removed), have a right to
receive, upon exercise thereof at a price equal to the then current Purchase
Price multiplied by the number of one one-hundredths of a Preferred Share for
which a Right is then exercisable, in accordance with the terms of this
Agreement and in lieu of Preferred Shares, such number of Common Shares of the
Company as shall equal the result obtained by (A) multiplying the then current
Purchase Price by the number of one one-hundredths of a Preferred Share for
which a Right is then exercisable and dividing that product by (B) 50% of the
then current per share market price of the Company's Common Shares (determined
pursuant to Section 11(d) hereof) on the date such Person became an Acquiring
Person; provided, however, that if the transaction that would otherwise give
        --------  -------
rise to the foregoing adjustment is also subject to the provisions of Section 13
hereof, then only the provisions of Section 13 hereof shall apply and no
adjustment shall be made pursuant to this Section 11(a)(ii).  In the event that
any Person shall become an Acquiring Person and the Rights shall then be
outstanding, the Company shall not take any action which would eliminate or
diminish the benefits intended to be afforded by the Rights.

     Notwithstanding anything in this Agreement to the contrary, from and after
the time any Person becomes an Acquiring Person, any Rights beneficially owned
by (i) such Acquiring Person or an Associate or Affiliate of such Acquiring
Person, (ii) a transferee of such Acquiring Person (or of any such Associate or
Affiliate) who becomes a transferee after the Acquiring Person became such, or
(iii) a transferee of such Acquiring Person (or of any such Associate or
Affiliate) who becomes a transferee prior to or concurrently with the Acquiring
Person's becoming such and receives such Rights pursuant to either (A) a
transfer (whether or not for consideration) from the Acquiring Person to holders
of equity interests in such Acquiring Person or to any Person with whom the
Acquiring Person has any continuing agreement, arrangement or understanding
regarding the transferred Rights or (B) a transfer which the Board of Directors
of the Company has determined is part of a plan, arrangement or understanding
which has as a primary purpose or effect the avoidance of this Section
11(a)(ii), shall become null and void without any further action and no holder
of such Rights shall have any rights whatsoever with respect to such Rights,
whether under any provision of this Agreement or otherwise.  The Company shall
use all reasonable efforts to insure that the provisions of this Section
11(a)(ii) and Section 4(b) are complied with, but shall have no liability to any
holder of Right Certificates or other Person as a result of its failure to make
any determinations with respect to an Acquiring Person or its Affiliates,
Associates or transferees hereunder.  No Right Certificate shall be issued at
any time upon the transfer of any Rights to an Acquiring Person whose Rights
would be void pursuant to the preceding sentence or any Associate or Affiliate
thereof or to any nominee of such Acquiring Person, Associate or Affiliate; and
any Right Certificate delivered to the Rights Agent for transfer to an Acquiring
Person whose Rights would be void pursuant to the preceding sentence shall be
canceled.
<PAGE>
 
          (iii) In the event that there shall not be sufficient Common Shares
issued but not outstanding or authorized but unissued to permit the exercise in
full of the Rights in accordance with the foregoing subparagraph (ii), the
Company shall take all such action as may be necessary to authorize additional
Common Shares for issuance upon exercise of the Rights.  In the event that the
Company shall, after a good faith effort, be unable to take all such action as
may be necessary to authorize such additional Common Shares, the Company shall
substitute, for each Common Share that would otherwise be issuable upon exercise
of a Right, a number of Preferred Shares or fraction thereof such that the
current per share market price of one Preferred Share multiplied by such number
or fraction thereof is equal to the current per share market price of one Common
Share as of the date of issuance of such Preferred Shares or fraction thereof;
provided, however, that if the Company is further unable to cause the
- --------  -------
authorization of a sufficient number of Preferred Shares, then, in the event the
Rights become so exercisable, the Board of Directors may, but shall not be
required to, with respect to each Right (A) pay cash in an amount equal to the
Purchase Price, in lieu of issuing Common Shares and requiring payment therefor,
or (B) issue debt or equity securities or a combination thereof, having a value
equal to the Current Value of the Common Shares (as defined hereinafter), where
the value of such securities shall be determined by a nationally recognized
investment banking firm selected by the Board of Directors of the Company, and
require the payment of the Purchase Price, or (C) deliver any combination of
cash, property, Common Shares, Preferred Shares and/or other securities having a
value equal to the Current Value, and require payment of all or any requisite
portions of the Purchase Price.  The Current Value shall be the product of the
current market price per share of Common Shares (determined pursuant to Section
11(d) on the date of the occurrence of the event described above in subparagraph
(ii)) multiplied by the number of Common Shares for which the Right otherwise
would be exercisable if there were sufficient shares available.  To the extent
that the Company determines that some action need be taken pursuant to the
second sentence of this subparagraph (iii), the Board of Directors may
temporarily suspend the exercisability of the Rights for a period of up to 45
days following the date on which the event described in Section 11(a)(ii) shall
have occurred, in order to seek any authorization of additional Common Shares
and/or to decide the appropriate form of distribution to be made pursuant to the
above provision and to determine the value thereof.  In the event of any such
suspension, the Company shall issue a public announcement stating that the
exercisability of the Rights has been temporarily suspended.

     (b) In case the Company shall fix a record date for the issuance of rights,
options or warrants to all holders of Preferred Shares entitling them (for a
period expiring within 45 calendar days after such record date) to subscribe for
or purchase Preferred Shares (or shares having the same designations and the
powers, preferences and rights, and the qualifications, limitations and
restrictions as the Preferred Shares ("equivalent preferred shares")) or
securities convertible into Preferred Shares or equivalent preferred shares at a
price per Preferred Share or equivalent preferred share (or having a conversion
price per share, if a security convertible into Preferred Shares or equivalent
preferred shares) less than the then current per share market price of the
Preferred Shares (as defined in Section 11(d)) on such record date, the Purchase
Price to be in effect after such record date shall be determined by multiplying
the Purchase Price in effect immediately prior to such record date by a
fraction, the numerator of which shall be the number of Preferred Shares
outstanding on such record date plus the number of Preferred Shares which the
aggregate offering price of the total number of Preferred Shares and/or
<PAGE>
 
equivalent preferred shares so to be offered (and/or the aggregate initial
conversion price of the convertible securities so to be offered) would purchase
at such current market price and the denominator of which shall be the number of
Preferred Shares outstanding on such record date plus the number of additional
Preferred Shares and/or equivalent preferred shares to be offered for
subscription or purchase (or into which the convertible securities so to be
offered are initially convertible); provided, however, that in no event shall
                                    --------  -------
the consideration to be paid upon the exercise of one Right be less than the
aggregate par value of the shares of capital stock of the Company issuable upon
exercise of one Right.  In case such subscription price may be paid in a
consideration part or all of which shall be in a form other than cash, the value
of such consideration shall be as determined in good faith by the Board of
Directors of the Company, whose determination shall be described in a statement
filed with the Rights Agent.  Preferred Shares owned by or held for the account
of the Company shall not be deemed outstanding for the purpose of any such
computation.  Such adjustment shall be made successively whenever such a record
date is fixed; and in the event that such rights, options or warrants are not so
issued, the Purchase Price shall be adjusted to be the Purchase Price which
would then be in effect if such record date had not been fixed.

     (c) In case the Company shall fix a record date for the making of a
distribution to all holders of the Preferred Shares (including any such
distribution made in connection with a consolidation or merger in which the
Company is the continuing or surviving corporation) of evidences of indebtedness
or assets (other than a regular quarterly cash dividend or a dividend payable in
Preferred Shares) or subscription rights or warrants (excluding those referred
to in Section 11(b) hereof), the Purchase Price to be in effect after such
record date shall be determined by multiplying the Purchase Price in effect
immediately prior to such record date by a fraction, the numerator of which
shall be the then current per share market price of the Preferred Shares (as
defined in Section 11(d)) on such record date, less the fair market value (as
determined in good faith by the Board of Directors of the Company, whose
determination shall be described in a statement filed with the Rights Agent) of
the portion of the assets or evidences of indebtedness so to be distributed or
of such subscription rights or warrants applicable to one Preferred Share and
the denominator of which shall be such current per share market price of the
Preferred Shares; provided, however, that in no event shall the consideration to
                  --------  -------
be paid upon the exercise of one Right be less than the aggregate par value of
the shares of capital stock of the Company to be issued upon exercise of one
Right.  Such adjustments shall be made successively whenever such a record date
is fixed; and in the event that such distribution is not so made, the Purchase
Price shall again be adjusted to be the Purchase Price which would then be in
effect if such record date had not been fixed.

     (d)  (i)   For the purpose of any computation hereunder, the "current per
share market price" of any security (a "Security" for the purpose of this
Section 11(d)(i)) on any date shall be deemed to be the average of the daily
closing prices per share of such Security for the 30 consecutive Trading Days
(as such term is hereinafter defined) immediately prior to such date; provided,
                                                                      --------
however, that in the event that the current per share market price of the
- -------
Security is determined during a period following the announcement by the issuer
of such Security of (A) a dividend or distribution on such Security payable in
shares of such Security or securities convertible into such shares, or (B) any
subdivision, combination or reclassification of such Security or securities
convertible into such shares, or (C) any subdivision, combination or
<PAGE>
 
reclassification of such Security and prior to the expiration of 30 Trading Days
after the ex-dividend date for such dividend or distribution, or the record date
for such subdivision, combination or reclassification, then, and in each such
case, the current per share market price shall be appropriately adjusted to
reflect the current market price per share equivalent of such Security.  The
closing price for each day shall be the last sale price, regular way, or, in
case no such sale takes place on such day, the average of the closing bid and
asked prices, regular way, in either case as reported in the principal
consolidated transaction reporting system with respect to securities listed or
admitted to trading on the New York Stock Exchange or, if the Security is not
listed or admitted to trading on the New York Stock Exchange, as reported in the
principal consolidated transaction reporting system with respect to securities
listed on the principal national securities exchange on which the Security is
listed or admitted to trading or as reported on the Nasdaq National Market or,
if the Security is not listed or admitted to trading on any national securities
exchange or reported on the Nasdaq National Market, the last quoted price or, if
not so quoted, the average of the high bid and low asked prices in the over-the-
counter market, as reported by the National Association of Securities Dealers,
Inc. Automated Quotations System ("Nasdaq") or such other system then in use,
or, if on any such date the Security is not quoted by any such organization, the
average of the closing bid and asked prices as furnished by a professional
market maker making a market in the Security selected by the Board of Directors
of the Company.  The term "Trading Day" shall mean a day on which the principal
national securities exchange on which the Security is listed or admitted to
trading is open for the transaction of business or, if the Security is not
listed or admitted to trading on any national securities exchange, a Business
Day.

          (ii)  For the purpose of any computation hereunder, the "current per
share market price" of the Preferred Shares shall be determined in accordance
with the method set forth in Section 11(d)(i).  If the Preferred Shares are not
publicly traded, the "current per share market price" of the Preferred Shares
shall be conclusively deemed to be the current per share market price of the
Common Shares as determined pursuant to Section 11(d)(i) (appropriately adjusted
to reflect any stock split, stock dividend or similar transaction occurring
after the date hereof) multiplied by one hundred.  If neither the Common Shares
nor the Preferred Shares are publicly held or so listed or traded, "current per
share market price" shall mean the fair value per share as determined in good
faith by the Board of Directors of the Company, whose determination shall be
described in a statement filed with the Rights Agent.

     (e) No adjustment in the Purchase Price shall be required unless such
adjustment would require an increase or decrease of at least 1% in the Purchase
Price; provided, however, that any adjustments which by reason of this Section
       --------  -------
11(e) are not required to be made shall be carried forward and taken into
account in any subsequent adjustment.  All calculations under this Section 11
shall be made to the nearest cent or to the nearest one one-hundredth of a
Preferred Share or one ten-thousandth of any other share or security as the case
may be.  Notwithstanding the first sentence of this Section 11(e), any
adjustment required by this Section 11 shall be made no later than the earlier
of (i) three years from the date of the transaction which requires such
adjustment or (ii) the date of the expiration of the right to exercise any
Rights.

     (f) If as a result of an adjustment made pursuant to Section 11(a) hereof,
the holder of any Right thereafter exercised shall become entitled to receive
any shares of capital stock of
<PAGE>
 
the Company other than Preferred Shares, thereafter the number of such other
shares so receivable upon exercise of any Right shall be subject to adjustment
from time to time in a manner and on terms as nearly equivalent as practicable
to the provisions with respect to the Preferred Shares contained in Section
11(a) through (c), inclusive, and the provisions of Sections 7, 9, 10, 13 and 14
with respect to the Preferred Shares shall apply on like terms to any such other
shares.

     (g) All Rights originally issued by the Company subsequent to any
adjustment made to the Purchase Price hereunder shall evidence the right to
purchase, at the adjusted Purchase Price, the number of one one-hundredths of a
Preferred Share purchasable from time to time hereunder upon exercise of the
Rights, all subject to further adjustment as provided herein.

     (h) Unless the Company shall have exercised its election as provided in
Section 11(i), upon each adjustment of the Purchase Price as a result of the
calculations made in Section 11(b) and (c), each Right outstanding immediately
prior to the making of such adjustment shall thereafter evidence the right to
purchase, at the adjusted Purchase Price, that number of one one-hundredths of a
Preferred Share (calculated to the nearest one one-millionth of a Preferred
Share) obtained by (i) multiplying (x) the number of one one-hundredths of a
Preferred Share covered by a Right immediately prior to this adjustment by (y)
the Purchase Price in effect immediately prior to such adjustment of the
Purchase Price and (ii) dividing the product so obtained by the Purchase Price
in effect immediately after such adjustment of the Purchase Price.

     (i) The Company may elect on or after the date of any adjustment of the
Purchase Price to adjust the number of Rights, in substitution for any
adjustment in the number of one one-hundredths of a Preferred Share purchasable
upon the exercise of a Right.  Each of the Rights outstanding after such
adjustment of the number of Rights shall be exercisable for the number of one
one-hundredths of a Preferred Share for which a Right was exercisable
immediately prior to such adjustment.  Each Right held of record prior to such
adjustment of the number of Rights shall become that number of Rights
(calculated to the nearest one ten-thousandth) obtained by dividing the Purchase
Price in effect immediately prior to adjustment of the Purchase Price by the
Purchase Price in effect immediately after adjustment of the Purchase Price.
The Company shall make a public announcement of its election to adjust the
number of Rights, indicating the record date for the adjustment, and, if known
at the time, the amount of the adjustment to be made.  This record date may be
the date on which the Purchase Price is adjusted or any day thereafter, but, if
the Right Certificates have been issued, shall be at least 10 days later than
the date of the public announcement.  If Right Certificates have been issued,
upon each adjustment of the number of Rights pursuant to this Section 11(i), the
Company shall, as promptly as practicable, cause to be distributed to holders of
record of Right Certificates on such record date Right Certificates evidencing,
subject to Section 14 hereof, the additional Rights to which such holders shall
be entitled as a result of such adjustment, or, at the option of the Company,
shall cause to be distributed to such holders of record in substitution and
replacement for the Right Certificates held by such holders prior to the date of
adjustment, and upon surrender thereof, if required by the Company, new Right
Certificates evidencing all the Rights to which such holders shall be entitled
after such adjustment.  Right Certificates so to be distributed shall be issued,
executed and countersigned in the manner provided for herein
<PAGE>
 
and shall be registered in the names of the holders of record of Right
Certificates on the record date specified in the public announcement.

     (j) Irrespective of any adjustment or change in the Purchase Price or the
number of one one-hundredths of a Preferred Share issuable upon the exercise of
the Rights, the Right Certificates theretofore and thereafter issued may
continue to express the Purchase Price and the number of one one-hundredths of a
Preferred Share which were expressed in the initial Right Certificates issued
hereunder.

     (k) Before taking any action that would cause an adjustment reducing the
Purchase Price below one one-hundredth of the then par value, if any, of the
Preferred Shares issuable upon exercise of the Rights, the Company shall take
any corporate action which may, in the opinion of its counsel, be necessary in
order that the Company may validly and legally issue fully paid and
nonassessable Preferred Shares at such adjusted Purchase Price.

     (l) In any case in which this Section 11 shall require that an adjustment
in the Purchase Price be made effective as of a record date for a specified
event, the Company may elect to defer until the occurrence of such event the
issuing to the holder of any Right exercised after such record date of the
Preferred Shares and other capital stock or securities of the Company, if any,
issuable upon such exercise on the basis of the Purchase Price in effect prior
to such adjustment; provided, however, that the Company shall deliver to such
                    --------  -------
holder a due bill or other appropriate instrument evidencing such holder's right
to receive such additional shares upon the occurrence of the event requiring
such adjustment.

     (m) The Company covenants and agrees that, after the Distribution Date, it
will not, except as permitted by Section 23 or Section 27 hereof, take (or
permit any Subsidiary to take) any action the purpose of which is to, or if at
the time such action is taken it is reasonably foreseeable that the effect of
such action is to, materially diminish or eliminate the benefits intended to be
afforded by the Rights.

     (n) Anything in this Section 11 to the contrary notwithstanding, the
Company shall be entitled to make such reductions in the Purchase Price, in
addition to those adjustments expressly required by this Section 11, as and to
the extent that it in its sole discretion shall determine to be advisable in
order that any consolidation or subdivision of the Preferred Shares, issuance
wholly for cash of any Preferred Shares at less than the current market price,
issuance wholly for cash of Preferred Shares or securities which by their terms
are convertible into or exchangeable for Preferred Shares, dividends on
Preferred Shares payable in Preferred Shares or issuance of rights, options or
warrants referred to hereinabove in Section 11(b), hereafter made by the Company
to holders of its Preferred Shares shall not be taxable to such stockholders.

     (o) In the event that at any time after the date of this Agreement and
prior to the Distribution Date, the Company shall (i) declare or pay any
dividend on the Common Shares payable in Common Shares or (ii) effect a
subdivision, combination or consolidation of the Common Shares (by
reclassification or otherwise than by payment of dividends in Common Shares)
into a greater or lesser number of Common Shares, then in any such case (A) the
<PAGE>
 
number of one one-hundredths of a Preferred Share purchasable after such event
upon proper exercise of each Right shall be determined by multiplying the number
of one one-hundredths of a Preferred Share so purchasable immediately prior to
such event by a fraction, the numerator of which is the number of Common Shares
outstanding immediately before such event and the denominator of which is the
number of Common Shares outstanding immediately after such event, and (B) each
Common Share outstanding immediately after such event shall have issued with
respect to it that number of Rights which each Common Share outstanding
immediately prior to such event had issued with respect to it.  The adjustments
provided for in this Section 11(o) shall be made successively whenever such a
dividend is declared or paid or such a subdivision, combination or consolidation
is effected.

     (p) The exercise of Rights under Section 11(a)(ii) shall only result in the
loss of rights under Section 11(a)(ii) to the extent so exercised and shall not
otherwise affect the rights represented by the Rights under this Rights
Agreement, including the rights represented by Section 13.

     SECTION 12.  CERTIFICATE OF ADJUSTED PURCHASE PRICE OR NUMBER OF SHARES.
Whenever an adjustment is made as provided in Sections 11 and 13 hereof, the
Company shall promptly (a) prepare a certificate setting forth such adjustment,
and a brief statement of the facts accounting for such adjustment, (b) file with
the Rights Agent and with each transfer agent for the Common Shares or the
Preferred Shares a copy of such certificate and (c) mail a brief summary thereof
to each holder of a Right Certificate in accordance with Section 25 hereof.  The
Rights Agent shall be fully protected in relying on any such certificate and on
any adjustment therein contained and shall not be deemed to have knowledge of
any adjustment unless and until it shall have received such certificate.

     SECTION 13.  CONSOLIDATION, MERGER OR SALE OR TRANSFER OF ASSETS OR EARNING
POWER.

     (a) In the event that, following the Shares Acquisition Date, directly or
indirectly (x) the Company shall consolidate with, or merge with and into, any
other Person (other than Wohlstadter), (y) any Person (other than Wohlstadter)
shall consolidate with the Company, or merge with and into the Company, and the
Company shall be the continuing or surviving corporation of such merger (other
than, in the case of either transaction described in (x) or (y), a merger or
consolidation which would result in all of the voting power represented by the
securities of the Company outstanding immediately prior thereto continuing to
represent (either by remaining outstanding or by being converted into securities
of the surviving entity) all of the voting power represented by the securities
of the Company or such surviving entity outstanding immediately after such
merger or consolidation and the holders of such securities not having changed as
a result of such merger or consolidation), or (z) the Company shall sell,
mortgage or otherwise transfer (or one or more of its subsidiaries shall sell,
mortgage or otherwise transfer), in one or more transactions, assets or earning
power aggregating more than 50% of the assets or earning power of the Company
and its subsidiaries (taken as a whole) to any other Person, (other than
Wohlstadter, the Company or any Subsidiary of the Company in one or more
transactions each of which individually and the aggregate does not violate
Section 13(d) hereof) then, and in each such case, proper provision shall be
made so that (i) following the Distribution Date, each holder of a Right,
subject to Section 11(a)(ii), shall have the right to receive, upon
<PAGE>
 
the exercise thereof at a price equal to the then current Purchase Price
multiplied by the number of one one-hundredths of a Preferred Share for which a
Right is then exercisable in accordance with the terms of this Agreement and in
lieu of Preferred Shares, such number of shares of freely tradeable Common
Shares of the Principal Party (as hereinafter defined), free and clear of liens,
rights of call or first refusal, encumbrances or other adverse claims, as shall
be equal to the result obtained by (A) multiplying the then current Purchase
Price by the number of one one-hundredths of a Preferred Share for which a Right
is then exercisable (without taking into account any adjustment previously made
pursuant to Section 11(a)(ii) hereof) and dividing that product by (B) 50% of
the then current per share market price of the Common Shares of such Principal
Party (determined pursuant to Section 11(d) hereof) on the date of consummation
of such consolidation, merger, sale or transfer; (ii) such Principal Party shall
thereafter be liable for, and shall assume, by virtue of such consolidation,
merger, sale or transfer, all the obligations and duties of the Company pursuant
to this Agreement; (iii) the term "Company" shall thereafter be deemed to refer
to such Principal Party, it being specifically intended that the provisions of
Section 11 hereof shall apply to such Principal Party; and (iv) such Principal
Party shall take such steps (including, but not limited to, the reservation of a
sufficient number of shares of its Common Shares in accordance with Section 9
hereof) in connection with such consummation as may be necessary to assure that
the provisions hereof shall thereafter be applicable, as nearly as reasonably
may be, in relation to its Common Shares thereafter deliverable upon the
exercise of the Rights.

     (b)  "Principal Party" shall mean:

          (i)   in the case of any transaction described in (x) or (y) of the
     first sentence of Section 13(a), the Person that is the issuer of any
     securities into which Common Shares of the Company are converted in such
     merger or consolidation, and if no securities are so issued, the Person
     that is the other party to the merger or consolidation (including, if
     applicable, the Company, if it is the surviving corporation); and

          (ii)  in the case of any transaction described in (z) of the first
     sentence in Section 13(a), the Person that is the party receiving the
     greatest portion of the assets or earning power transferred pursuant to
     such transaction or transactions;

provided, however, that in any case, (1) if the Common Shares of such Person are
- --------  -------
not at such time and have not been continuously over the preceding 12-month
period registered under Section 12 of the Exchange Act, and such Person is a
direct or indirect subsidiary or Affiliate of another Person the Common Shares
of which are and have been so registered, "Principal Party" shall refer to such
other Person; (2) in case such Person is a subsidiary, directly or indirectly,
or Affiliate of more than one Person, the Common Shares of two or more of which
are and have been so registered, "Principal Party" shall refer to whichever of
such Persons is the issuer of the Common Shares having the greatest aggregate
market value; and (3) in case such Person is owned, directly or indirectly, by a
joint venture formed by two or more Persons that are not owned, directly or
indirectly, by the same Person, the rules set forth in (1) and (2) above shall
apply to each of the chains of ownership having an interest in such joint
venture as if such party were a "subsidiary" of both or all of such joint
venturers and the Principal Parties
<PAGE>
 
in each such chain shall bear the obligations set forth in this Section 13 in
the same ratio as their direct or indirect interests in such Person bear to the
total of such interests.

     (c) The Company shall not consummate any such consolidation, merger, sale
or transfer unless the Principal Party shall have a sufficient number of
authorized shares of its Common Shares that have not been issued or reserved for
issuance to permit the exercise in full of the Rights in accordance with this
Section 13 and unless prior thereto the Company and each Principal Party and
each other Person who may become a Principal Party as a result of such
consolidation, merger, sale or transfer shall have executed and delivered to the
Rights Agent a supplemental agreement providing for the terms set forth in
paragraphs (a) and (b) of this Section 13 and further providing that, as soon as
practicable after the date of any consolidation, merger, sale or transfer of
assets mentioned in paragraph (a) of this Section 13, the Principal Party at its
own expense will:

          (i)   prepare and file a registration statement under the Act with
     respect to the Rights and the securities purchasable upon exercise of the
     Rights on an appropriate form, will use its best efforts to cause such
     registration statement to become effective as soon as practicable after
     such filing and will use its best efforts to cause such registration
     statement to remain effective (with a prospectus at all times meeting the
     requirements of the Act) until the Final Expiration Date;

          (ii)  use its best efforts to qualify or register the Rights and the
     securities purchasable upon exercise of the Rights under the blue sky laws
     of such jurisdictions as may be necessary or appropriate; and

          (iii) deliver to holders of the Rights historical financial
     statements for the Principal Party and each of its Affiliates which
     comply in all material respects with the requirements for registration on
     Form 10 under the Exchange Act.

The provisions of this Section 13 shall similarly apply to successive mergers or
consolidations or sales or other transfers.

     (d) After the Distribution Date, the Company covenants and agrees that it
shall not (i) consolidate with, (ii) merge with or into, or (iii) sell or
transfer to, in one or more transactions, assets or earning power aggregating
more than 50% of the assets or earning power of the Company and its subsidiaries
taken as a whole, any other Person (other than a Subsidiary of the Company in a
transaction which does not violate Section 11(m) hereof), if (x) at the time of
or after such consolidation, merger or sale there are any charter or bylaw
provisions or any rights, warrants or other instruments or securities
outstanding, agreements in effect or any other action taken which would diminish
or otherwise eliminate the benefits intended to be afforded by the Rights or (y)
prior to, simultaneously with or immediately after such consolidation, merger or
sale, the stockholders of the Person who constitutes, or would constitute, the
"Principal Party" for purposes of Section 13(a) hereof shall have received a
distribution of Rights previously owned by such Person or any of its Affiliates
and Associates.  The Corporation shall not consummate any such consolidation,
merger, sale or transfer unless prior
<PAGE>
 
thereto the Company and such other Person shall have executed and delivered to
the Rights Agent a supplemental agreement evidencing compliance with this
Section 13(d).

     SECTION 14.  FRACTIONAL RIGHTS AND FRACTIONAL SHARES.

     (a) The Company shall not be required to issue fractions of Rights or to
distribute Right Certificates which evidence fractional Rights.  In lieu of such
fractional Rights, there shall be paid to the registered holders of the Right
Certificates with regard to which such fractional Rights would otherwise be
issuable, an amount in cash equal to the same fraction of the current market
value of a whole Right.  For the purposes of this Section 14(a), the current
market value of a whole Right shall be the closing price of the Rights for the
Trading Day immediately prior to the date on which such fractional Rights would
have been otherwise issuable.  The closing price for any day shall be the last
sale price, regular way, or, in case no such sale takes place on such day, the
average of the closing bid and asked prices, regular way, in either case as
reported in the principal consolidated transaction reporting system with respect
to securities listed or admitted to trading on the New York Stock Exchange or,
if the Rights are not listed or admitted to trading on the New York Stock
Exchange, as reported in the principal consolidated transaction reporting system
with respect to securities listed on the principal national securities exchange
on which the Rights are listed or admitted to trading or as reported on the
Nasdaq National Market or, if the Rights are not listed or admitted to trading
on any national securities exchange or reported on the Nasdaq National Market,
the last quoted price or, if not so quoted, the average of the high bid and low
asked prices in the over-the-counter market, as reported by Nasdaq or such other
system then in use or, if on any such date the Rights are not quoted by any such
organization, the average of the closing bid and asked prices as furnished by a
professional market maker making a market in the Rights selected by the Board of
Directors of the Company.  If on any such date no such market maker is making a
market in the Rights, the fair value of the Rights on such date as determined in
good faith by the Board of Directors of the Company shall be used.

     (b) The Company shall not be required to issue fractions of Preferred
Shares (other than fractions which are integral multiples of one one-hundredth
of a Preferred Share) upon exercise of the Rights or to distribute certificates
which evidence fractional Preferred Shares (other than fractions which are
integral multiples of one one-hundredth of a Preferred Share).  Fractions of
Preferred Shares in integral multiples of one one-hundredth of a Preferred Share
may, at the election of the Company, be evidenced by depositary receipts;
provided, however, that holders of such depositary receipts shall have all of
- --------  -------
the designations and the powers, preferences and rights, and the qualifications,
limitations and restrictions to which they are entitled as beneficial owners of
the Preferred Shares represented by such depositary receipts.  In lieu of
fractional Preferred Shares that are not integral multiples of one one-hundredth
of a Preferred Share, the Company shall pay to the registered holders of Right
Certificates at the time such Rights are exercised as herein provided an amount
in cash equal to the same fraction of the current market value of one Preferred
Share.  For the purposes of this Section 14(b), the current market value of a
Preferred Share shall be the current per share market price of the Preferred
Shares (as determined pursuant to the second sentence of Section 11(d)(i)
hereof) for the Trading Day immediately prior to the date of such exercise (or,
if not publicly traded, in accordance with Section 11(d)(ii)).
<PAGE>
 
     (c) Following the occurrence of one of the transactions or events specified
in Section 11 giving rise to the right to receive Common Shares, capital stock
equivalents (other than Preferred Shares) or other securities upon the exercise
of a Right, the Company shall not be required to issue fractions of Common
Shares or units of such Common Shares, capital stock equivalents or other
securities upon exercise of the Rights or to distribute certificates which
evidence fractional Common Shares, capital stock equivalents or other
securities.  In lieu of fractional Common Shares, capital stock equivalents or
other securities, the Company shall pay to the registered holders of Right
Certificates at the time such Rights are exercised as herein provided an amount
in cash equal to the same fraction of the current market value of one Common
Share or unit of such Common Shares, capital stock equivalents or other
securities.  For purposes of this Section 14(c), the current market value shall
be the current per share market price (as determined pursuant to Section
11(d)(i) hereof) for the Trading Day immediately prior to the date of such
exercise and, if such capital stock equivalent is not traded, each such capital
stock equivalent shall have the value of one one-hundredth of a Preferred Share.

     (d) The holder of a Right by the acceptance of the Right expressly waives
his right to receive any fractional Rights or any fractional shares upon
exercise of a Right (except as provided above).

     SECTION 15.  RIGHTS OF ACTION.  All rights of action in respect of this
Agreement, excepting the rights of action given to the Rights Agent under
Sections 18 and 20 hereof, are vested in the respective registered holders of
the Right Certificates (and, prior to the Distribution Date, the registered
holders of the Common Shares) and any registered holder of any Right Certificate
(or, prior to the Distribution Date, of the Common Shares), without the consent
of the Rights Agent or of the holder of any other Right Certificate (or, prior
to the Distribution Date, of the Common Shares), may, in his own behalf and for
his own benefit, enforce, and may institute and maintain any suit, action or
proceeding against the Company to enforce, or otherwise act in respect of, his
right to exercise the Rights evidenced by such Right Certificate in the manner
provided in such Right Certificate and in this Agreement.  Without limiting the
foregoing or any remedies available to the holders of Rights, it is specifically
acknowledged that the holders of Rights would not have an adequate remedy at law
for any breach of this Agreement and will be entitled to specific performance of
the obligations under, and injunctive relief against actual or threatened
violations of the obligations of any Person subject to, this Agreement.  Holders
of Rights shall be entitled to recover the reasonable costs and expenses,
including attorneys fees, incurred by them in any action to enforce the
provisions of this Agreement.

     SECTION 16.  AGREEMENT OF RIGHT HOLDERS.  Every holder of a Right, by
accepting the same, consents and agrees with the Company and the Rights Agent
and with every other holder of a Right that:

          (a) prior to the Distribution Date, the Rights will be transferable
only in connection with the transfer of the Common Shares;
<PAGE>
 
          (b) after the Distribution Date, the Right Certificates are
transferable only on the registry books of the Rights Agent if surrendered at
the principal office of the Rights Agent, duly endorsed or accompanied by a
proper instrument of transfer; and

          (c) the Company and the Rights Agent may deem and treat the person in
whose name the Right Certificate (or, prior to the Distribution Date, the
associated Common Shares certificate) is registered as the absolute owner
thereof and of the Rights evidenced thereby (notwithstanding any notations of
ownership or writing on the Right Certificates or the associated Common Shares
certificate made by anyone other than the Company or the Rights Agent) for all
purposes whatsoever, and neither the Company nor the Rights Agent shall be
affected by any notice to the contrary.

     SECTION 17.  RIGHT CERTIFICATE HOLDER NOT DEEMED A STOCKHOLDER.  No holder,
as such, of any Right Certificate shall be entitled to vote, receive dividends
or be deemed for any purpose the holder of the Preferred Shares or any other
securities of the Company which may at any time be issuable on the exercise of
the Rights represented thereby, nor shall anything contained herein or in any
Right Certificate be construed to confer upon the holder of any Right
Certificate, as such, any of the rights of a stockholder of the Company or any
right to vote for the election of directors or upon any matter submitted to
stockholders at any meeting thereof, or to give or withhold consent to any
corporate action, or to receive notice of meetings or other actions affecting
stockholders (except as provided in Section 25 hereof), or to receive dividends
or subscription rights, or otherwise, until the Right or Rights evidenced by
such Right Certificate shall have been exercised in accordance with the
provisions hereof.

     SECTION 18.  CONCERNING THE RIGHTS AGENT.  The Company agrees to pay to the
Rights Agent reasonable compensation for all services rendered by it hereunder
and, from time to time, on demand of the Rights Agent, its reasonable expenses
and counsel fees and other disbursements incurred in the administration and
execution of this Agreement and the exercise and performance of its duties
hereunder.  The Company also agrees to indemnify the Rights Agent for, and to
hold it harmless against, any loss, liability, or expense, incurred without
negligence, bad faith or willful misconduct on the part of the Rights Agent, for
anything done or omitted by the Rights Agent in connection with the acceptance
and administration of this Agreement, including the costs and expenses of
defending against any claim of liability in the premises.  The indemnity
provided herein shall survive the expiration of the Rights and the termination
of this Agreement.

     The Rights Agent shall be protected and shall incur no liability for, or in
respect of any action taken, suffered or omitted by it in connection with, its
administration of this Agreement in reliance upon any Right Certificate or
certificate for the Preferred Shares or Common Shares or for other securities of
the Company, instrument of assignment or transfer, power of attorney,
endorsement, affidavit, letter, notice, direction, consent, certificate,
statement, or other paper or document believed by it to be genuine and to be
signed, executed and, where necessary, verified or acknowledged, by the proper
person or persons, or otherwise upon the advice of counsel as set forth in
Section 20 hereof.
<PAGE>
 
     SECTION 19.  MERGER OR CONSOLIDATION OR CHANGE OF NAME OF RIGHTS AGENT.
Any corporation into which the Rights Agent or any successor Rights Agent may be
merged or with which it may be consolidated, or any corporation resulting from
any merger or consolidation to which the Rights Agent or any successor Rights
Agent shall be a party, or any corporation succeeding to the shareholder
services or corporate trust business of the Rights Agent or any successor Rights
Agent, shall be the successor to the Rights Agent under this Agreement without
the execution or filing of any paper or any further act on the part of any of
the parties hereto, provided, however that such corporation would be eligible
                    --------  -------
for appointment as a successor Rights Agent under the provisions of Section 21
hereof.  In case at the time such successor Rights Agent shall succeed to the
agency created by this Agreement any of the Right Certificates shall have been
countersigned but not delivered, any such successor Rights Agent may adopt the
countersignature of the predecessor Rights Agent and deliver such Right
Certificates so countersigned; and in case at that time any of the Right
Certificates shall not have been countersigned, any successor Rights Agent may
countersign such Right Certificates either in the name of the predecessor Rights
Agent or in the name of the successor Rights Agent; and in all such cases such
Right Certificates shall have the full force provided in the Right Certificates
and in this Agreement.

     In case at any time the name of the Rights Agent shall be changed and at
such time any of the Right Certificates shall have been countersigned but not
delivered, the Rights Agent may adopt the countersignature under its prior name
and deliver Right Certificates so countersigned; and in case at that time any of
the Right Certificates shall not have been countersigned, the Rights Agent may
countersign such Right Certificates either in its prior name or in its changed
name; and in all such cases such Right Certificates shall have the full force
provided in the Right Certificates and in this Agreement.

     SECTION 20.  DUTIES OF RIGHTS AGENT.  The Rights Agent undertakes the
duties and obligations imposed by this Agreement upon the following terms and
conditions, by all of which the Company and the holders of Right Certificates,
by their acceptance thereof, shall be bound:

     (a) The Rights Agent may consult with legal counsel of its choice (who may
be legal counsel for the Company), and the opinion of such counsel shall be full
and complete authorization and protection to the Rights Agent as to any action
taken or omitted by it in good faith and in accordance with such opinion.

     (b) Whenever in the performance of its duties under this Agreement the
Rights Agent shall deem it necessary or desirable that any fact or matter be
proved or established by the Company prior to taking or suffering any action
hereunder, such fact or matter (unless other evidence in respect thereof be
herein specifically prescribed) may be deemed to be conclusively proved and
established by a certificate signed by any one of the Chairman of the Board, the
Chief Executive Officer, the President, the Chief Financial Officer, any Vice
President, the Treasurer or the Secretary of the Company and delivered to the
Rights Agent; and such certificate shall be full authorization to the Rights
Agent for any action taken or suffered in good faith by it under the provisions
of this Agreement in reliance upon such certificate.
<PAGE>
 
     (c) The Rights Agent shall be liable hereunder to the Company and any other
Person only for its own negligence, bad faith or willful misconduct.

     (d) The Rights Agent shall not be liable for or by reason of any of the
statements of fact or recitals contained in this Agreement or in the Right
Certificates (except its countersignature thereof) or be required to verify the
same, but all such statements and recitals are and shall be deemed to have been
made by the Company only.

     (e) The Rights Agent shall not be under any responsibility in respect of
the validity of this Agreement or the execution and delivery hereof (except the
due execution hereof by the Rights Agent) or in respect of the validity or
execution of any Right Certificate (except its countersignature thereof); nor
shall it be responsible for any breach by the Company of any covenant or
condition contained in this Agreement or in any Right Certificate; nor shall it
be responsible for any change in the exercisability of the Rights (including the
Rights becoming void pursuant to Section 11(a)(ii) hereof) or any adjustment in
the terms of the Rights (including the manner, method or amount thereof)
provided for in Section 3, 11, 13, 23 or 24, or the ascertaining of the
existence of facts that would require any such change or adjustment (except with
respect to the exercise of Rights evidenced by Right Certificates after receipt
of a certificate pursuant to Section 12 describing such change or adjustment);
nor shall it by any act hereunder be deemed to make any representation or
warranty as to the authorization or reservation of any Preferred Shares to be
issued pursuant to this Agreement or any Right Certificate or as to whether any
Preferred Shares will, when issued, be validly authorized and issued, fully paid
and nonassessable.

     (f) The Company agrees that it will perform, execute, acknowledge and
deliver or cause to be performed, executed, acknowledged and delivered all such
further and other acts, instruments and assurances as may reasonably be required
by the Rights Agent for the carrying out or performing by the Rights Agent of
the provisions of this Agreement.

     (g) The Rights Agent is hereby authorized and directed to accept
instructions with respect to the performance of its duties hereunder from any
one of the Chairman of the Board, the Chief Executive Officer, the President,
the Chief Financial Officer, any Vice President, the Secretary or the Treasurer
of the Company, and to apply to such officers for advice or instructions in
connection with its duties, and it shall not be liable for any action taken or
suffered by it in good faith in accordance with instructions of any such officer
or for any delay in acting while waiting for those instructions.  Any
application by the Rights Agent for written instructions from the Company may,
at the option of the Rights Agent, set forth in writing any action proposed to
be taken or omitted by the Rights Agent with respect to its duties or
obligations under this Rights Agreement and the date on and/or after which such
action shall be taken or omitted and the Rights Agent shall not be liable for
any action taken or omitted in accordance with a proposal included in any such
application on or after the date specified therein (which date shall not be less
than three business days after the date indicated in such application unless any
such officer shall have consented in writing to an earlier date) unless, prior
to taking or omitting any such action, the Rights Agent has received written
instructions in response to such application specifying the action to be taken
or omitted.
<PAGE>
 
     (h) The Rights Agent and any stockholder, director, officer or employee of
the Rights Agent may buy, sell or deal in any of the Rights or other securities
of the Company or become pecuniarily interested in any transaction in which the
Company may be interested, or contract with or lend money to the Company or
otherwise act as fully and freely as though it were not Rights Agent under this
Agreement.  Nothing herein shall preclude the Rights Agent from acting in any
other capacity for the Company or for any other legal entity.

     (i) The Rights Agent may execute and exercise any of the rights or powers
hereby vested in it or perform any duty hereunder either itself or by or through
its attorneys or agents, and the Rights Agent shall not be answerable or
accountable for any act, default, neglect or misconduct of any such attorneys or
agents or for any loss to the Company resulting from any such act, default,
neglect or misconduct, provided reasonable care was exercised in the selection
and continued employment thereof.

     (j) No provision of this Agreement shall require the Rights Agent to expend
or risk its own funds or otherwise incur any financial liability in the
performance of any of its duties hereunder or in the exercise of its rights if
there shall be reasonable grounds for believing that repayment of such funds or
adequate indemnification against such risk or liability is not reasonably
assured to it.

     (k) If, with respect to any Right Certificate surrendered to the Rights
Agent for exercise or transfer, the certificate attached to the form of
assignment or form of election to purchase, as the case may be, has not been
executed, the Rights Agent shall not take any further action with respect to
such requested exercise of transfer without first consulting with the Company.

     SECTION 21.  CHANGE OF RIGHTS AGENT.  The Rights Agent or any successor
Rights Agent may resign and be discharged from its duties under this Agreement
upon 30 days' notice in writing mailed to the Company and to each transfer agent
for the Common Shares or Preferred Shares by registered or certified mail, and
to the holders of the Right Certificates by first-class mail.  The Company may
remove the Rights Agent or any successor Rights Agent upon 30 days' notice in
writing, mailed to the Rights Agent or successor Rights Agent, as the case may
be, and to each transfer agent for the Common Shares or Preferred Shares by
registered or certified mail, and to the holders of the Right Certificates by
first-class mail.  If the Rights Agent shall resign or be removed or shall
otherwise become incapable of acting, the Company shall appoint a successor to
the Rights Agent.  If the Company shall fail to make such appointment within a
period of 30 days after giving notice of such removal or after it has been
notified in writing of such resignation or incapacity by the resigning or
incapacitated Rights Agent or by the holder of a Right Certificate (who shall,
with such notice, submit his Right Certificate for inspection by the Company),
then the registered holder of any Right Certificate may apply to any court of
competent jurisdiction for the appointment of a new Rights Agent.  Any successor
Rights Agent, whether appointed by the Company or by such a court, shall be a
corporation organized and doing business under the laws of the United States or
of any other state of the United States which is authorized under such laws to
exercise corporate trust or stock transfer powers and is subject to supervision
or examination by federal or state authority and which has at the time of its
appointment as Rights Agent a combined capital and surplus of at least $50
million.  After
<PAGE>
 
appointment, the successor Rights Agent shall be vested with the same powers,
rights, duties and responsibilities as if it had been originally named as Rights
Agent without further act or deed; but the predecessor Rights Agent shall
deliver and transfer to the successor Rights Agent any property at the time held
by it hereunder, and execute and deliver any further assurance, conveyance, act
or deed necessary for the purpose.  Not later than the effective date of any
such appointment the Company shall file notice thereof in writing with the
predecessor Rights Agent and each transfer agent for the Common Shares or
Preferred Shares, and mail a notice thereof in writing to the registered holders
of the Right Certificates.  Failure to give any notice provided for in this
Section 21, however, or any defect therein, shall not affect the legality or
validity of the resignation or removal of the Rights Agent or the appointment of
the successor Rights Agent, as the case may be.

     SECTION 22.  ISSUANCE OF NEW RIGHT CERTIFICATES.  Notwithstanding any of
the provisions of this Agreement or of the Rights to the contrary, the Company
may, at its option, issue new Right Certificates evidencing Rights in such form
as may be approved by its Board of Directors to reflect any adjustment or change
in the Purchase Price and the number or kind or class of shares or other
securities or property purchasable under the Right Certificates made in
accordance with the provisions of this Agreement.  In addition, in connection
with the issuance or sale of Common Shares following the Distribution Date and
prior to the earlier of the Redemption Date and the Final Expiration Date, the
Company (a) shall with respect to Common Shares so issued or sold pursuant to
the exercise of stock options or under any employee plan or arrangement, or upon
the exercise, conversion or exchange of securities, notes or debentures issued
by the Company, and (b) may, in any other case, if deemed necessary or
appropriate by the Board of Directors of the Company, issue Right Certificates
representing the appropriate number of Rights in connection with such issuance
or sale; provided, however, that (i) the Company shall not be obligated to issue
         --------  -------
any such Right Certificates if, and to the extent that, the Company shall be
advised by counsel that such issuance would create a significant risk of
material adverse tax consequences to the Company or the Person to whom such
Right Certificate would be issued, and (ii) no Right Certificate shall be issued
if, and to the extent that, appropriate adjustment shall otherwise have been
made in lieu of the issuance thereof.

     SECTION 23.  REDEMPTION.

     (a) The Rights may be redeemed by action of the Board of Directors pursuant
to subsection (b) of this Section 23 and shall not be redeemed in any other
manner.

     (b)  (i)   The Board of Directors of the Company may, at its option, at any
time prior to the earlier of (A) the Shares Acquisition Date; or (B) the Final
Expiration Date, redeem all but not less than all the then outstanding Rights at
a redemption price of $.01 per Right, appropriately adjusted to reflect any
stock split, stock dividend or similar transaction occurring after the date
hereof (such redemption price being hereinafter referred to as the "Redemption
Price"), and the Company may, at its option, pay the Redemption Price in Common
Shares (based on the "current per share market price," as defined in Section
11(d) hereof, of the Common Shares at the time of redemption), cash or any other
form of consideration deemed appropriate by the Board of Directors.  The
redemption of the Rights by the Board of Directors may be made effective at such
time, on such basis and subject to such conditions as the Board
<PAGE>
 
of Directors in its sole discretion may establish.  Notwithstanding anything
contained in this Agreement to the contrary, the Rights shall not be exercisable
pursuant to Section 11(a)(ii) hereof prior to the expiration or termination of
the Company's right of redemption hereunder.

          (ii)  In addition, the Board of Directors of the Company may, at its
option, at any time after the time a person becomes an Acquiring Person and
the expiration of any period during which the holder of Rights may exercise
the rights under Section 11(a)(ii) but prior to any event described in (x),
(y) or (z) of the first sentence of Section 13, redeem all but not less than
all of the then outstanding Rights at the Redemption Price (x) in connection
with any merger, consolidation or sale or other transfer (in one transaction
or in a series of related transactions) of assets or earning power aggregating
50% or more of the earning power of the Company and its subsidiaries (taken as
a whole) in which all holders of Common Shares are treated alike and not
involving (other than as a holder of Common Shares being treated like all
other such holders) an Interested Stockholder or a Transaction Person or
(y)(A) if and for so long as the Acquiring Person is not thereafter the
Beneficial Owner of 15% or more of the Company's then outstanding Common
Shares, and (B) at the time of redemption no other Persons are Acquiring
Persons.

     (c) Immediately upon the action of the Board of Directors of the Company
ordering the redemption of the Rights pursuant to subsection (b) of this Section
23, and without any further action and without any notice, the right to exercise
the Rights will terminate and the only right thereafter of the holders of Rights
shall be to receive the Redemption Price.  The Company shall promptly give
public notice of any such redemption; provided, however, that the failure to
                                      --------  -------
give, or any defect in, any such notice shall not affect the validity of such
redemption.  Within 10 days after such action of the Board of Directors ordering
the redemption of the Rights pursuant to subsection (b) the Company shall mail a
notice of redemption to all the holders of the then outstanding Rights at their
last addresses as they appear upon the registry books of the Rights Agent or,
prior to the Distribution Date, on the registry books of the transfer agent for
the Common Shares.  Any notice which is mailed in the manner herein provided
shall be deemed given, whether or not the holder receives the notice.  Each such
notice of redemption will state the method by which the payment of the
Redemption Price will be made.  Neither the Company nor any of its Affiliates or
Associates may redeem, acquire or purchase for value any Rights at any time in
any manner other than that specifically set forth in this Section 23 or in
Section 24 hereof, and other than in connection with the purchase of Common
Shares prior to the Distribution Date.

     (d) The Company may, at its option, discharge all of its obligations with
respect to the Rights by (i) issuing a press release announcing the manner of
redemption of the Rights and (ii) mailing payment of the Redemption Price to the
registered holders of the Rights at their last addresses as they appear on the
registry books of the Rights Agent or, prior to the Distribution Date, on the
registry books of the transfer agent for the Common Shares, and upon such
action, all outstanding Right Certificates shall be null and void without any
further action by the Company.
<PAGE>
 
     SECTION 24.  EXCHANGE.

     (a) The Board of Directors of the Company may, at its option, at any time
after any Person becomes an Acquiring Person, exchange all or part of the then
outstanding and exercisable Rights (which shall not include Rights that have
become void pursuant to the provisions of Section 11(a)(ii) hereof) for Common
Shares at an exchange ratio of one Common Share per Right, appropriately
adjusted to reflect any stock split, stock dividend or similar transaction
occurring after the date hereof (such exchange ratio being hereinafter referred
to as the "Exchange Ratio").  Notwithstanding the foregoing, the Board of
Directors shall not be empowered to effect such exchange at any time after any
Person (other than the Company, any Subsidiary of the Company, any employee
benefit plan of the Company or any such Subsidiary, or any entity holding Common
Shares for or pursuant to the terms of any such plan), together with all
Affiliates and Associates of such Person, becomes the Beneficial Owner of 50% or
more of the Common Shares then outstanding.

     (b) Immediately upon the action of the Board of Directors of the Company
ordering the exchange of any Rights pursuant to subsection (a) of this Section
24 and without any further action and without any notice, the right to exercise
such Rights shall terminate and the only right thereafter of a holder of such
Rights shall be to receive that number of Common Shares equal to the number of
such Rights held by such holder multiplied by the Exchange Ratio.  The Company
shall promptly give public notice of any such exchange; provided, however, that
                                                        --------  -------
the failure to give, or any defect in, such notice shall not affect the validity
of such exchange.  The Company promptly shall mail a notice of any such exchange
to all of the holders of such Rights at their last addresses as they appear upon
the registry books of the Rights Agent.  Any notice which is mailed in the
manner herein provided shall be deemed given, whether or not the holder receives
the notice.  Each such notice of exchange will state the method by which the
exchange of the Common Shares for Rights will be effected and, in the event of
any partial exchange, the number of Rights which will be exchanged.  Any partial
exchange shall be effected pro rata based on the number of Rights (other than
Rights which have become void pursuant to the provisions of Section 11(a)(ii)
hereof) held by each holder of Rights.

     (c) In the event that there shall not be sufficient Common Shares issued
but not outstanding or authorized but unissued to permit any exchange of Rights
as contemplated in accordance with this Section 24, the Company shall take all
such action as may be necessary to authorize additional Common Shares for
issuance upon exchange of the Rights.  In the event that the Company shall,
after a good faith effort, be unable to take all such action as may be necessary
to authorize such additional Common Shares, the Company shall substitute, for
each Common Share that would otherwise be issuable upon exchange of a Right, a
number of Preferred Shares or fraction thereof such that the current per share
market price of one Preferred Share multiplied by such number or fraction
thereof multiplied by such number or fraction is equal to the current per share
market price of one Common Share as of the date of issuance of such Preferred
Shares or fraction thereof; provided, however, that if the Company is further
                            --------  -------
unable to cause the authorization of a sufficient number of additional Common
Shares, then, in the event the Rights become so exchangeable, the Board of
Directors may, but shall not be required to, with respect to each Right (A) pay
cash in an amount equal to the current per share market price of one Common
Share (determined pursuant to Section 11(d) on the date of the
<PAGE>
 
occurrence of the event described in Section 11(a)(ii)) in exchange for each
Right, in lieu of issuing Common Shares, or (B) issue debt or equity securities
or a combination thereof, having a value equal to the current per share market
price of one Common Share (determined pursuant to Section 11(d) on the date of
the occurrence of the event described in Section 11(a)(ii)) where the value of
such securities shall be determined by a nationally recognized investment
banking firm selected by the Board of Directors of the Company, in exchange for
each Right, or (C) deliver any combination of cash, property, Common Shares
and/or other securities having a value equal to the current per share market
price of one Common Share (determined pursuant to Section 11(d) on the date of
the occurrence of the event described in Section 11(2)(ii)) in exchange for each
Right.  To the extent that the Company determines that some action need be taken
pursuant to the second sentence of this Section 24(c), the Board of Directors
may temporarily suspend the exercisability of the Rights for a period of up to
45 days following the date on which the event described in Section 11(a)(ii)
shall have occurred, in order to seek any authorization of additional Common
Shares and/or to decide the appropriate form of distribution to be made pursuant
to the above provision and to determine the value thereof.  In the event of any
such suspension, the Company shall issue a public announcement stating that the
exercisability of the Rights has been temporarily suspended.

     (d) The Company shall not be required to issue fractions of Common Shares
or to distribute certificates which evidence fractional Common Shares.  In lieu
of such fractional Common Shares, the Company shall pay to the registered
holders of the Right Certificates with regard to which such fractional Common
Shares would otherwise be issuable an amount in cash equal to the same fraction
of the current market value of a whole Common Share.  For the purposes of this
subsection (d), the current market value of a whole Common Share shall be the
closing price of a Common Share (as determined pursuant to the second sentence
of Section 11(d)(i) hereof) for the Trading Day immediately after the date of
the first public announcement by the Company that an exchange is to be effected
pursuant to this Section 24.

     (e) The Company shall not be required to issue fractions of Preferred
Shares (other than fractions which are integral multiples of one one-hundredth
of a Preferred Share) upon exchange of the Rights or to distribute certificates
which evidence fractional Preferred Shares (other than fractions which are
integral multiples of one one-hundredth of a Preferred Share).  Fractions of
Preferred Shares in integral multiples of one one-hundredth of a Preferred Share
may, at the election of the Company, be evidenced by depositary receipts;
provided, however, that holders of such depositary receipts shall have all of
- --------  -------
the designations and the powers, preferences and rights, and the qualifications,
limitations and restrictions to which they are entitled as beneficial owners of
the Preferred Shares represented by such depositary receipts.  In lieu of
fractional Preferred Shares that are not integral multiples of one one-hundredth
of a Preferred Share, the Company shall pay to the registered holders of Right
Certificates at the time such Rights are exercised as herein provided an amount
in cash equal to the same fraction of the current market value of one Preferred
Share.  For the purposes of this Section 24(e), the current market value of a
Preferred Share shall be the closing price of a Preferred Share (as determined
pursuant to the second sentence of Section 11(d)(i) hereof) for the Trading Day
immediately after  the date of the first public announcement by the Company that
an exchange is to be effected pursuant to this Section 24.
<PAGE>
 
     SECTION 25.  NOTICE OF CERTAIN EVENTS.

     (a) In case the Company shall propose (i) to pay any dividend payable in
stock of any class to the holders of its Preferred Shares or to make any other
distribution to the holders of its Preferred Shares (other than a regular
quarterly cash dividend), (ii) to offer to the holders of its Preferred Shares
rights or warrants to subscribe for or to purchase any additional Preferred
Shares or shares of stock of any class or any other securities, rights or
options, (iii) to effect any reclassification of its Preferred Shares (other
than a reclassification involving only the subdivision of outstanding Preferred
Shares), (iv) to effect any consolidation or merger into or with, or to effect
any sale or other transfer (or to permit one or more of its Subsidiaries to
effect any sale or other transfer), in one or more transactions, of 50% or more
of the assets or earning power of the Company and its Subsidiaries (taken as a
whole), to any other Person, (v) to effect the liquidation, dissolution or
winding up of the Company, or (vi) to declare or pay any dividend on the Common
Shares payable in Common Shares or to effect a subdivision, combination or
consolidation of the Common Shares (by reclassification or otherwise than by
payment of dividends in Common Shares), then, in each such case, the Company
shall give to each holder of a Right Certificate, in accordance with Section 26
hereof, a notice of such proposed action, which shall specify the record date
for the purpose of such stock dividend, or distribution of rights or warrants,
or the date on which such reclassification, consolidation, merger, sale,
transfer, liquidation, dissolution, or winding up is to take place and the date
of participation therein by the holders of the Common Shares and/or the
Preferred Shares, if any such date is to be fixed, and such notice shall be so
given in the case of any action covered by clause (i) or (ii) above at least 10
days prior to the record date for determining holders of the Preferred Shares
for purposes of such action, and in the case of any such other action, at least
10 days prior to the date of the taking of such proposed action or the date of
participation therein by the holders of the Common Shares and/or the Preferred
Shares, whichever shall be the earlier.

     (b) In case the event set forth in Section 11(a)(ii) hereof shall occur,
then the Company shall as soon as practicable thereafter give to each holder of
a Right Certificate, in accordance with Section 26 hereof, a notice of the
occurrence of such event, which notice shall describe the event and the
consequences of the event to holders of Rights under Section 11(a)(ii) hereof.

     SECTION 26.  NOTICES.  Notices or demands authorized by this Agreement to
be given or made by the Rights Agent or by the holder of any Right Certificate
to or on the Company shall be sufficiently given or made if sent by first-class
mail, postage prepaid, addressed (until another address is filed in writing with
the Rights Agent) as follows:

               IGEN INTERNATIONAL, INC.
               1620 Industrial Drive
               Gaithersburg, MD  20877
               Attention:  Secretary

Subject to the provisions of Section 21 hereof, any notice or demand authorized
by this Agreement to be given or made by the Company or by the holder of any
Right Certificate to or
<PAGE>
 
on the Rights Agent shall be sufficiently given or made if sent by first-class
mail, postage prepaid, addressed (until another address is filed in writing with
the Company) as follows:

               THE FIRST NATIONAL BANK OF BOSTON
               Mail Stop 450264
               Blue Hills Office Park
               150 Royall Street
               Canton, MA  02021
               Attention:  Investor Relations

Notices or demands authorized by this Agreement to be given or made by the
Company or the Rights Agent to the holder of any Right Certificate shall be
sufficiently given or made if sent by first-class mail, postage prepaid,
addressed to such holder at the address of such holder as shown on the registry
books of the Company.

     SECTION 27.  SUPPLEMENTS AND AMENDMENTS.  The Company may from time to time
supplement or amend this Agreement without the approval of any holders of Right
Certificates in order to cure any ambiguity, to correct or supplement any
provision contained herein which may be defective or inconsistent with any other
provisions herein, or to make any other provisions with respect to the Rights
which the Company may deem necessary or desirable, any such supplement or
amendment to be evidenced by a writing signed by the Company and the Rights
Agent; provided, however, that from and after such time as any Person becomes an
       --------  -------
Acquiring Person, this Agreement shall not be amended in any manner which would
adversely affect the interests of the holders of Rights.  Without limiting the
foregoing, the Company may at any time prior to such time as any Person becomes
an Acquiring Person amend this Agreement to lower the thresholds set forth in
Sections 1(a) and 3(a) hereof from 15% to any percentage which is (i) greater
than the largest percentage of the outstanding Common Shares then known by the
Company to be beneficially owned by any Person (other than an Excluded Person)
and (ii) not less than 10%.  Upon delivery of a certificate from an appropriate
officer of the Company which states that the proposed supplement or amendment is
in compliance with the terms of this Section 27, the Rights Agent shall execute
such supplement or amendment unless the Rights Agent shall have determined in
good faith that such supplement or amendment would adversely affect its interest
under this Agreement.  Prior to the Distribution Date, the interests of the
holders of Rights shall be deemed coincident with the interests of the holders
of Common Shares.

     SECTION 28.  DETERMINATION AND ACTIONS BY THE BOARD OF DIRECTORS, ETC.  For
all purposes of this Agreement, any calculation of the number of Common Shares
outstanding at any particular time, including for purposes of determining the
particular percentage of such outstanding Common Shares or any other securities
of which any Person is the Beneficial Owner, shall be made in accordance with
the last sentence of Rule 13d-3(d)(1)(i) of the General Rules and Regulations
under the Exchange Act as in effect on the date of this Agreement.  The Board of
Directors of the Company shall have the exclusive power and authority to
administer this Agreement and to exercise all rights and powers specifically
granted to the Board, or the Company, or as may be necessary or advisable in the
administration of this Agreement, including without limitation, the right and
power to (i) interpret the provisions of this
<PAGE>
 
Agreement, and (ii) make all determinations deemed necessary or advisable for
the administration of this Agreement (including a determination to redeem or not
redeem the Rights or to amend the Agreement).  All such actions, calculations,
interpretations and determinations (including, for purposes of clause (y) below,
all omissions with respect to the foregoing) which are done or made by the Board
in good faith, shall (x) be final, conclusive and binding on the Rights Agent
and the holders of the Right Certificates, and (y) not subject the Board to any
liability to the holders of the Right Certificates.

     SECTION 29.  SUCCESSORS.  All the covenants and provisions of this
Agreement by or for the benefit of the Company or the Rights Agent shall bind
and inure to the benefit of their respective successors and assigns hereunder.

     SECTION 30.  BENEFITS OF THIS AGREEMENT.  Nothing in this Agreement shall
be construed to give to any person or corporation other than the Company, the
Rights Agent and the registered holders of the Right Certificates (and, prior to
the Distribution Date, the Common Shares) any legal or equitable right, remedy
or claim under this Agreement; but this Agreement shall be for the sole and
exclusive benefit of the Company, the Rights Agent and the registered holders of
the Right Certificates (and, prior to the Distribution Date, the Common Shares).

     SECTION 31.  SEVERABILITY.  If any term, provision, covenant or restriction
of this Agreement is held by a court of competent jurisdiction or other
authority to be invalid, void or unenforceable, the remainder of the terms,
provisions, covenants and restrictions of this Agreement shall remain in full
force and effect and shall in no way be affected, impaired or invalidated.

     SECTION 32.  GOVERNING LAW.  This Agreement and each Right Certificate
issued hereunder shall be deemed to be a contract made under the laws of the
State of Delaware and for all purposes shall be governed by and construed in
accordance with the laws of such State applicable to contracts to be made and
performed entirely within such State.

     SECTION 33.  COUNTERPARTS.  This Agreement may be executed in any number of
counterparts and each of such counterparts shall for all purposes be deemed to
be an original, and all such counterparts shall together constitute but one and
the same instrument.

     SECTION 34.  DESCRIPTIVE HEADINGS.  Descriptive headings of the several
Sections of this Agreement are inserted for convenience only and shall not
control or affect the meaning or construction of any of the provisions hereof.
<PAGE>
 
     IN WITNESS WHEREOF, parties whereto have caused this Agreement to be duly
executed and their seals attested, all as of the day and year first above
written.

ATTEST:                             IGEN INTERNATIONAL, INC.


_____________________________       ____________________________________ 
Andrei M. Manoliu                   Richard J. Massey, Ph.D.
Secretary                           President and Chief Operating Officer


_____________________________       ____________________________________ 
ATTEST:                             THE FIRST NATIONAL BANK OF BOSTON



By: _________________________           By:_____________________________

Title: ______________________           Title: _________________________


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