CUBIST PHARMACEUTICALS INC
8-K, 1999-07-30
PHARMACEUTICAL PREPARATIONS
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                       SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549

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

                                    FORM 8-K

                                 CURRENT REPORT
                     PURSUANT TO SECTION 13 OR 15(D) OF THE
                         SECURITIES EXCHANGE ACT OF 1934


                Date of Report (Date of earliest event reported):
                                  JULY 21, 1999
                                 ----------------


                           CUBIST PHARMACEUTICALS, INC
                           ---------------------------
               (Exact Name of Registrant as Specified in Charter)


         DELAWARE                   0-21379           22-3192085
- -------------------------------------------------------------------------------
 (State or Other Jurisdiction     (Commission      (IRS Employer
       of Incorporation)          File Number)        Identification No.)

                 24 EMILY STREET, CAMBRIDGE, MASSACHUSETTS 02139
                 -----------------------------------------------
               (Address of Principal Executive Offices) (Zip Code)

       Registrant's telephone number, including area code: (617) 576-1999


<PAGE>


ITEM 5.  OTHER EVENTS.


         On July 21, 1999, the Board of Directors of Cubist Pharmacueticals,
Inc. (the "COMPANY") declared a dividend of one fractional preferred share
purchase right (a "RIGHT") for each outstanding share of common stock, par value
$0.001 per share (the "COMMON SHARES"), of the Company. The dividend is payable
on August 3, 1999 (the "RECORD DATE") to the stockholders of record on that
date. Except as described below, each Right, when exercisable, entitles the
registered holder to purchase from the Company one one-hundredth of a share of
Series A Junior Participating Preferred Stock of the Company, par value $0.001
per share (the "PREFERRED SHARES"), at a price of $20 per one one-hundredth of a
Preferred Share (the "PURCHASE PRICE"), subject to adjustment or substitution of
other securities of the Company in place of the Preferred Shares. The
description and terms of the Rights are set forth in a Rights Agreement (the
"RIGHTS AGREEMENT") between the Company and BankBoston, N.A., as Rights Agent
(the "RIGHTS AGENT").

         Initially, the Rights will be attached to all certificates representing
Common Shares then outstanding, and no separate Rights certificates will be
distributed. Until the earlier to occur of (i) 10 business days following a
public announcement that a person or group of affiliated or associated persons
(an "ACQUIRING PERSON") have acquired beneficial ownership of 15% or more of the
outstanding Common Shares (the date of such an announcement being a "SHARES
ACQUISITION DATE"), 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
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
such outstanding Common Shares (in either case, (i) or (ii), 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
certificates together with a copy of this Summary of Rights.

         The Rights Agreement provides that, until the Distribution Date, 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 for transfer of any certificates for
Common Shares outstanding as of the Record Date, even without such notation or a
copy of this Summary of Rights being attached thereto, 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 ("RIGHTS CERTIFICATES") will be mailed to
holders of record of the Common Shares as of the close of business on the
Distribution Date, and the separate Rights Certificates alone will evidence the
Rights.


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                                      -2-


         The Rights are not exercisable until the Distribution Date. The Rights
will expire on August, 2009 (the "FINAL EXPIRATION DATE"), unless the Rights are
earlier redeemed by the Company, 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 $1 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.

         If, after the first date of public announcement by the Company or an
Acquiring Person that an Acquiring Person has become such, the Company is
involved in a merger or other business combination transaction in which the
Common Shares are exchanged or changed, or 50% or more of the Company's
consolidated assets or earning power are sold (in one transaction or a series of


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                                      -3-



transactions), proper provision will be made so that each holder of a Right
(other than an Acquiring Person) 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 (or, in the event
there is more than one acquiring company, the acquiring company receiving the
greatest portion of the assets or earning power transferred) which at the time
of such transaction would have a market value of two times the exercise price of
the Right.

         If any person becomes an Acquiring Person, each holder of a Right 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. UPON
OCCURRENCE OF ANY OF THE EVENTS DESCRIBED IN THE IMMEDIATELY PRECEDING SENTENCE,
ANY RIGHTS THAT ARE, OR (UNDER CERTAIN CIRCUMSTANCES SPECIFIED IN THE RIGHTS
AGREEMENT) WERE, BENEFICIALLY OWNED BY ANY ACQUIRING PERSON SHALL IMMEDIATELY
BECOME NULL AND VOID.

         At any time after the occurrence of any such event and prior to the
acquisition by such person or group of 50% or more of the outstanding Common
Shares, the Board of Directors may exchange the Rights (other than Rights owned
by such person or group which 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 (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) will be issued
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 earlier of (i) the tenth day after a Shares
Acquisition Date, or (ii) the expiration of the Rights, the Board of Directors
may redeem the Rights in whole, but not in part, at a price of $0.0001 per Right
(the "REDEMPTION PRICE"). The redemption of the Rights may be made effective at
such time on such basis and with such conditions as the Board of Directors in
its sole discretion may establish. 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.

         Other than those provisions relating to the principal economic terms of
the Rights, any of the provisions of the Rights Agreement may be amended by the
Board of Directors of the Company prior to the Distribution Date. After the
Distribution Date, the provisions of the Rights Agreement may be amended by the
Board in order to cure any ambiguity, to make changes that do not adversely
affect the interests of holders of Rights (excluding the interests of any
Acquiring Person), or to shorten or lengthen any time period under the Rights
Agreement; PROVIDED,


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                                      -4-


HOWEVER, that no amendment to adjust the time period governing redemption shall
be made at such time as the Rights are not redeemable.

         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.

         The Rights have certain anti-takeover effects. The Rights will cause
substantial dilution to a person or group that attempts to acquire the Company
on terms not approved by the Company's Board of Directors. The Rights should not
interfere with any merger or other business combination approved by the Board of
Directors in light of the ability of the Board of Directors to redeem the
Rights or amend the Rights Agreement as summarized above.

         The form of Rights Agreement between the Company and the Rights Agent
specifying the terms of the Rights, which includes as Exhibit B the form of
Rights Certificate, is attached hereto as an exhibit and incorporated herein by
reference. The foregoing description of the Rights does not purport to be
complete and is qualified in its entirety by reference to the Rights Agreement.


ITEM 7.  FINANCIAL STATEMENTS, PRO FORMA FINANCIAL INFORMATION AND
         EXHIBITS.

(c)      Exhibits.

         99.1  Rights Agreement, dated as of July 21, 1999 between the Company
and BankBoston, N.A., as Rights Agent.

         99.2  Press Release, dated July 23, 1999.

         99.3  Form of Certificate of Designations, included as Exhibit A to
item 99.1 above.

         99.4  Form of Rights Certificate, included as Exhibit B to item 99.1
above.

         99.5  Summary of Rights, included as Exhibit C to item 99.1 above.


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                                      -5-


                                   SIGNATURES

         Pursuant to the requirements of the Securities Exchange Act of 1934,
the Registrant has duly caused this report to be signed on its behalf by the
undersigned hereunto duly authorized.

                             CUBIST PHARMACUETICALS, INC.



                             By:  /s/ Thomas A. Shea
                                  ----------------------------------------------
                                  Thomas A. Shea
                                  Vice President Administration & Finance, Chief
                                  Financial Officer and Treasurer



Date:  July 29, 1999


<PAGE>


                                                                    EXHIBIT 99.1

                                RIGHTS AGREEMENT

         This Rights Agreement (this "AGREEMENT"), dated as of July 21, 1999, is
by and between Cubist Pharmaceuticals, Inc. (the "COMPANY"), a Delaware
corporation, and BankBoston, N.A. (the "RIGHTS AGENT"), a national banking
association.

         The Company's Board of Directors has declared a dividend of one
preferred share purchase right (a "RIGHT") in respect of each share of the
Company's Common Stock outstanding of record as of the close of business, Boston
time, on August 3, 1999 (the "RECORD DATE"), each Right representing the right
to purchase one one-hundredth of a Preferred Share, upon the terms and subject
to the conditions set forth in this Agreement, 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.

         The parties hereby agree as follows:

         1.  CERTAIN DEFINITIONS.  For purposes of this Agreement:

         (a) "ACQUIRING PERSON" means any Person who, together with all
Affiliates and Associates of such Person, is the Beneficial Owner of 15% or more
of the Common Shares of the Company then outstanding or who was such a
Beneficial Owner at any time after the date hereof, whether or not such Person
continues to be the Beneficial Owner of 15% or more of the Common Shares then
outstanding, but will not include the Company, any Subsidiary of the Company,
any employee benefit plan of the Company or any Subsidiary of the Company, or
any entity holding securities of the Company organized, appointed, or
established by the Company or any Subsidiary for or pursuant to the terms of any
such plan. Notwithstanding the foregoing, (i) Sofinov Societe Financiere
D'Innovation ("Sofinov") will not be deemed to be an "Acquiring Person" so long
as Sofinov and its Affiliates together own less than 22% of the then
outstanding Common Shares of the Company, and (ii) no Person will become an
"Acquiring Person" solely 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 becomes 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 after
such share purchases by the Company, becomes the Beneficial Owner of any
additional Common Shares of the Company, then such Person will be deemed to be
an "Acquiring Person." Notwithstanding the foregoing, if the Board of Directors
of the Company 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 Rights Agreement.


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                                      -2-


         (b) "ADJUSTMENT SHARES" shall have the meaning ascribed thereto in
Section 11(a)(ii) hereof.


         (c) "AFFILIATE" and "ASSOCIATE" 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.

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

             (i) that such Person or any of such Person's Affiliates or
         Associates, directly or indirectly, has the right to acquire (whether
         such right is exercisable immediately or only after the passage of
         time) pursuant to any agreement, arrangement, or understanding (whether
         or not in writing) or upon the exercise of conversion rights, exchange
         rights, rights, warrants or options, or otherwise; PROVIDED, HOWEVER,
         that a Person will not be deemed the "Beneficial Owner" of, or to
         "beneficially own," (A) securities tendered pursuant to a tender or
         exchange offer made by such Person or any of such Person's Affiliates
         or Associates until such tendered securities are accepted for payment,
         purchase, or exchange, or (B) at any time prior to the occurrence of a
         Triggering Event, securities issuable upon exercise of Rights, or (C)
         from and after the occurrence of a Triggering Event, securities
         issuable upon exercise of Rights, which Rights were acquired by such
         Person or any of such Person's Affiliates or Associates prior to the
         Distribution Date or pursuant to Section 3(a) or Section 23 hereof (the
         "ORIGINAL RIGHTS") or pursuant to Section 11(i) hereof in connection
         with an adjustment made with respect to any Original Rights;

              (ii) that such Person or any of such Person's Affiliates or
         Associates, directly or indirectly, has the right to vote or dispose of
         or has "beneficial ownership" of (as determined pursuant to Rule 13d-3
         of the General Rules and Regulations under the Exchange Act), including
         without limitation pursuant to any agreement, arrangement, or
         understanding, whether or not in writing; PROVIDED, HOWEVER, that a
         Person will not be deemed the "Beneficial Owner" of, or to
         "beneficially own," any security under this subparagraph (ii) as a
         result of an oral or written agreement, arrangement, or understanding
         to vote such security if such agreement, arrangement, or understanding:
         (A) arises solely from a revocable proxy given in response to a public
         proxy or consent solicitation made pursuant to, and in accordance with,
         the applicable provisions of the General Rules and Regulations under
         the Exchange Act, and (B) is not also then reportable by such Person on
         Schedule 13D under the Exchange Act (or any comparable or successor
         report); or

             (iii) that are beneficially owned, directly or indirectly, by any
         other Person (or any Affiliate or Associate thereof) with which such
         Person (or any of such Person's Affiliates or Associates) has any
         agreement, arrangement or understanding (whether or not in writing),
         for the purpose of acquiring, holding, voting (except pursuant to a
         revocable proxy as described in the proviso to subparagraph (ii) of
         this paragraph (d)) or disposing of any voting securities of the
         Company.


<PAGE>
                                      -3-


PROVIDED, HOWEVER, that nothing in this paragraph (d) will cause a Person
engaged in business as an underwriter of securities to be the "Beneficial Owner"
of, or to "beneficially own," any securities acquired through such Person's
participation in good faith in a firm commitment underwriting until the
expiration of forty days after the date of such acquisition.

         (e) "BUSINESS DAY" means any day other than a Saturday, a Sunday, or a
day on which banking institutions in The Commonwealth of Massachusetts are
authorized or obligated by law or executive order to close.

         (f) "CLOSE OF BUSINESS" on any given date means 5:00 P.M., Boston time,
on such date; PROVIDED, HOWEVER, that if such date is not a Business Day it
means 5:00 P.M., Boston time, on the next succeeding Business Day.

         (g) "COMMON SHARES" when used with reference to the Company means the
shares of common stock, par value $0.001 per share, of the Company. "Common
Shares" when used with reference to any Person other than the Company means the
capital stock with the greatest voting power, or the equity securities or other
equity interest having power to control or direct the management, of such other
Person, or if such other Person is a Subsidiary of another Person, of the Person
or Persons that ultimately control such first-mentioned Person and which have
issued and outstanding such capital stock, equity securities, or equity
interests.

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

         (i) "EXPIRATION DATE" has the meaning set forth in Section 7(a)(iii)
hereof.

         (j) "FINAL EXPIRATION DATE" has the meaning set forth in Section
7(a)(i) hereof.

         (k) "PERSON" means any individual, firm, corporation, partnership,
limited liability company, trust, or other entity, and includes any successor
(by merger or otherwise) of such entity.

         (l) "PREFERRED SHARES" means shares of Series A Junior Participating
Preferred Stock, par value $0.001 per share, of the Company having rights and
preferences set forth in the Form of Certificate of Designations attached to
this Rights Agreement as EXHIBIT A.

         (m) "PURCHASE PRICE" has the meaning set forth in Section 7(b) hereof.

         (n) "REDEMPTION DATE" has the meaning set forth in Section 7(a)(ii)
hereof.

         (o) "RIGHT" has the meaning set forth in the second paragraph hereof.

         (p) "RIGHTS CERTIFICATE" shall have the meaning ascribed thereto in
Section 3(a) hereof.

         (q) "SECTION 7(e) PERSON" has the meaning set forth in Section 7(e)
hereof.


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                                      -4-


         (r) "SECTION 11(a)(ii) EVENT" means any event described in Section 11
(a)(ii) hereof.

         (s) "SECTION 13 EVENT" means any event  described in clauses (x), (y),
or (z) of Section 13(a) hereof.

         (t) "SHARES ACQUISITION DATE" means the first date of public
announcement (which, for purposes of this definition, includes without
limitation a report filed pursuant to Section 13(d) under the Exchange Act) by
the Company or an Acquiring Person that an Acquiring Person has become such.

         (u) "SUBSIDIARY" of any Person means any other Person of which a
majority of the voting power of the voting equity securities or equity interest
is owned, directly or indirectly, by such first-mentioned Person, or which is
otherwise controlled by such first-mentioned Person.

         (v) "SUMMARY OF RIGHTS" shall have the meaning ascribed thereto in
Section 3(b) hereof.

         (w) "TRIGGERING EVENT" means any Section 11(a)(ii) Event or any Section
13 Event.

         (x) "VOTING STOCK" means (i) the Common Shares of the Company, and (ii)
any other shares of capital stock of the Company entitled to vote generally in
the election of directors or entitled to vote together with the Common Shares in
respect of any merger, consolidation, sale of all or substantially all of the
Company's assets, liquidation, dissolution, or winding-up. Whenever any
provision of this Agreement requires a determination of whether a number of
shares of Voting Stock constituting a specified percentage of such Voting Stock
has been voted, tendered, acquired, sold or otherwise disposed of, or a
determination of whether a Person has offered or proposed to acquire a number of
shares of Voting Stock constituting such specified percentage, the number of
shares of Voting Stock constituting such specified percentage of Voting Stock
will in every such case be deemed to be the number of shares of Voting Stock
constituting the specified percentage of the Company's entire voting power then
entitled to vote generally in the election of directors or then entitled to vote
together with the Common Shares in respect of any merger, consolidation, sale of
all or substantially all of the Company's assets, liquidation, dissolution, or
winding-up.

         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,
until the Distribution Date, will also be the holders of the Common Shares in
accordance with Section 3 hereof) in accordance with the terms and conditions
hereof; and the Rights Agent hereby accepts such appointment. The Company may
from time to time appoint such co-Rights Agents as it may deem necessary or
desirable, upon ten (10) days' prior written notice to the Rights Agent. The
Rights Agent shall have no duty to supervise, and shall in no event be liable
for, the acts or omissions of any such co-Rights Agent. In the event the Company
appoints one or more co-Rights Agents, the respective duties of the Rights
Agents and any co-Rights Agents will be as the Company may determine.


<PAGE>
                                      -5-


         SECTION 3. ISSUE OF RIGHTS CERTIFICATES.

         (a) Until the earliest of:

             (i)  the close of business on the tenth Business Day after 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 by any Person (other than the Company, any Subsidiary of
         the Company, any employee benefit plan of the Company or of any
         Subsidiary of the Company or any entity holding Common Shares for or
         pursuant to the terms of any such plan) of, or of the first public
         announcement of the intention of any Person (other than the Company,
         any Subsidiary of the Company, any employee benefit plan of the Company
         or of any Subsidiary of the Company or any entity holding Common Shares
         for or pursuant to the terms of any such plan) to commence, a tender or
         exchange offer, the consummation of which would result in any Person
         becoming the Beneficial Owner of Common Shares aggregating 15% or more
         of the then outstanding Common Shares;

(including any such date which is after the date of this Agreement and prior to
the issuance of the Rights; the earliest of such dates being herein referred to
as the "DISTRIBUTION DATE"):

             (x)  no right may be exercised;

             (y)  the Rights will be evidenced (subject to the provisions of
         Section 3(b) hereof) by the certificates for Common Shares registered
         in the names of the holders thereof (which certificates will also be
         deemed to be certificates for Rights) and not by separate certificates;
         and

             (z)  the Rights (and the right to receive certificates therefor)
         will be transferable only in connection with the transfer of the
         underlying 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 if requested, the Rights Agent will send) by first-class,
postage-prepaid mail or other appropriate means, 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 certificate for Rights, in
substantially the form of the attached EXHIBIT B (collectively, "RIGHTS
CERTIFICATES"), evidencing one Right for each Common Share so held. As of and
after the Distribution Date, the Rights will be evidenced solely by Rights
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 the attached EXHIBIT C (the "SUMMARY OF RIGHTS"), by
first-class, postage-prepaid mail, or other appropriate means, to each record
holder of Common Shares as of the Close


<PAGE>
                                      -6-


of Business on the Record Date, at the address of such holder shown on the
records of the Company or its transfer agent.

         With respect to certificates for Common Shares outstanding as of the
Record Date, until the Distribution Date (or earlier redemption, expiration or
termination of the Rights), the Rights will be evidenced by such certificates
registered in the names of the holders thereof together with a copy of the
Summary of Rights attached thereto, and the registered holders of the Common
Shares will also be the registered holders of the associated Rights. With
respect to uncertificated Common Shares outstanding as of the Record Date, until
the Distribution Date, the Rights will be evidenced by the registration of the
Common Shares in the Company's share register in the names of the holders
thereof.

         Until the Distribution Date (or earlier redemption, expiration or
termination of the Rights), the surrender for transfer of any certificate for
Common Shares outstanding on the Record Date, even without a copy of the Summary
of Rights attached thereto, will also constitute the transfer of the Rights
associated with the Common Shares represented by such certificate.

         (c) Certificates issued for Common Shares (including without limitation
certificates issued upon transfer or exchange of Common Shares) after the Record
Date but prior to the earlier of the Distribution Date, the Redemption Date, the
Expiration Date or the Final Expiration Date will be deemed also to be
certificates for Rights and will have impressed, printed, or written thereon, or
otherwise affixed thereto, the following legend:

         "This certificate also evidences and entitles the holder hereof to
         certain rights as set forth in a Rights Agreement between Cubist
         Pharmaceuticals, Inc. and BankBoston, N.A., dated as of July 21, 1999,
         (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 Cubist Pharmaceuticals, Inc. Under certain
         circumstances, as set forth in the Rights Agreement, such Rights may be
         redeemed, may expire, or may be evidenced by separate certificates and
         will no longer be evidenced by this certificate. Cubist
         Pharmaceuticals, Inc. will mail to the registered 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,
         under certain circumstances, Rights held by Acquiring Persons (as
         defined in the Rights Agreement), or certain related Persons, and any
         subsequent holder of such Rights, may become null and void."

and, in the case of the initial transaction or subsequent periodic statements
with respect to uncertificated Common Shares, the following legend:

         "The registration in the share register of Cubist Pharmaceuticals, Inc.
         of the shares of common stock to which this initial transaction or
         subsequent periodic statement relates also evidences and entitles the
         registered holder of such shares to certain rights as set forth in a
         Rights Agreement between Cubist Pharmaceuticals, Inc. and BankBoston,
         N.A., dated as of July 21, 1999, (the "RIGHTS AGREEMENT"), the terms of
         which are hereby incorporated


<PAGE>
                                      -7-


         herein by reference and a copy of which is on file at the principal
         executive offices of Cubist Pharmaceuticals, 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 such registration in the share register of Cubist Pharmaceuticals,
         Inc. Cubist Pharmaceuticals, Inc. will mail to the holder of this
         certificate a copy of the Rights Agreement without charge after
         receipt of a written request therefor. Under certain circumstances, as
         set forth in the Rights Agreement, Rights issued to any Person who
         becomes an Acquiring Person (as defined in the Rights Agreement) may
         become null and void."

         Until the Distribution Date, the Rights associated with Common Shares
will be evidenced only by the certificates representing such Common Shares, and
the surrender for transfer of any such certificate will also constitute the
transfer of the Rights associated with the Common Shares represented thereby.
However, with respect to such initial transaction or subsequent periodic
statements containing the foregoing legend, until the Distribution Date, the
Rights associated with the Common Shares with respect to which such statements
are issued shall be evidenced solely by the registration of ownership of such
Common Shares in the share register of the Company, and the registration of
transfer of ownership in such share register shall also constitute the transfer
of the Rights associated with the Common Shares whose ownership is so
transferred. 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 will be deemed cancelled and retired so that
the Company will not be entitled to exercise any Rights associated with the
Common Shares that are no longer outstanding.

         Notwithstanding anything to the contrary stated herein, no Rights
Certificate shall be issued pursuant to this Section 3 that represents Rights
"beneficially owned" by an Acquiring Person whose Rights would be void pursuant
to Section 7(e) or any Associate or Affiliate of any such Acquiring Person; no
Rights Certificate shall be issued at any time upon the transfer of any Rights
to an Acquiring Person whose Rights would be void pursuant to Section 7(e) or
any Associate or Affiliate thereof or to any nominee of such Acquiring Person,
Associate or Affiliate; any Rights Certificate delivered to the Rights Agent for
transfer to an Acquiring Person whose Rights would be void pursuant to Section
7(e) shall be canceled.

         SECTION 4. FORM OF RIGHTS CERTIFICATES. The Rights Certificates (and
the forms of election to purchase shares and of assignment to be printed on the
reverse thereof) will be substantially in the form of the attached EXHIBIT B,
and may have such marks of identification or designation and such legends,
summaries, or indorsements 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 or
securities quotation system on or by which the Rights may from time to time be
listed or quoted, or to conform to usage. Subject to the provisions of Section
11 and Section 23 hereof, the Rights Certificates initially will entitle the
holders thereof to purchase such number of one one-hundredths of a Preferred
Share as may be set forth therein at the price per one one-hundredth of a
Preferred Share set forth therein (the


<PAGE>
                                      -8-


"PURCHASE PRICE"), but the number of such one one-hundredths of a Preferred
Share and the Purchase Price will be subject to adjustment as provided herein.


         SECTION 5. COUNTERSIGNATURE AND REGISTRATION. The Rights Certificates
will be executed on behalf of the Company by such officer or officers who would
be entitled to sign certificates representing Preferred Shares, either manually
or by facsimile signature, may (but need not) have affixed thereto the Company's
seal or a facsimile thereof, and may (but need not) be attested by the Secretary
or an Assistant Secretary of the Company, either manually or by facsimile
signature. The Rights Certificates will be countersigned by the Rights Agent and
will not be valid for any purpose unless so countersigned. If any officer of the
Company who signed any of Rights Certificate ceases to be such officer of the
Company before countersignature by the Rights Agent and issuance and delivery by
the Company, such Rights Certificate, 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 Rights Certificate had not ceased to
be such officer of the Company; and any Rights Certificate may be signed on
behalf of the Company by any Person who, at the actual date of the execution of
such Rights Certificate, will be a proper officer of the Company to sign such
Rights 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 books for registration and transfer of the Rights Certificates, showing
the names and addresses of the respective holders of the Rights Certificates,
the number of Rights evidenced on its face by each of the Rights Certificates,
and the date of each Rights Certificate.

         SECTION 6. TRANSFER, SPLIT-UP, COMBINATION AND EXCHANGE OF RIGHTS
CERTIFICATES; MUTILATED, DESTROYED, LOST OR STOLEN RIGHTS CERTIFICATES. Subject
to the provisions of Sections 3(c), 4, 7(e), and 15 hereof, at any time after
the close of business on the Distribution Date, and before the close of business
on the Expiration Date, any Rights Certificate(s) may be transferred, split up,
combined, or exchanged for one or more new Rights Certificates entitling the
registered holder to purchase the same number of one one-hundredths of a
Preferred Share as the Rights Certificate(s) surrendered then entitled such
holder to purchase.

         Any registered holder desiring to transfer, split up, combine, or
exchange any Rights Certificate(s) will make such request in writing delivered
to the Rights Agent, and will surrender the Rights Certificate or Rights
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 respect to the
transfer, split up, combination or exchange of any such surrendered Rights
Certificate until the registered holder shall have completed and signed the
certificate contained in the form of assignment on the reverse side of such
Rights 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 will countersign and deliver to the Person entitled thereto one or more
Rights Certificates, as the case may be,


<PAGE>
                                      -9-


as so requested. The Company may require payment of a sum sufficient to cover
any tax or other governmental charge that may be imposed in connection with any
transfer, split-up, combination, or exchange of Rights 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 Rights
Certificate, and in case of loss, theft, or destruction, of indemnity and/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 Rights Certificate if mutilated, the Company will execute and deliver a new
Rights Certificate of like tenor to the Rights Agent for delivery to the
registered holder in lieu of the Rights Certificate so lost, stolen, destroyed,
or mutilated.

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

         (a) Subject to Section 7(e) hereof, the registered holder of any Rights
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 Rights 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 other
securities) as to which the Rights are being exercised, at or prior to the
earliest of:

             (i) the close of business on August 3, 2009 (the "FINAL EXPIRATION
         DATE");

             (ii) the time at which the Rights are redeemed as provided in
         Section 24 hereof (the "REDEMPTION DATE"); or

             (iii) the time at which such Rights are exchanged as provided
         in Section 25 hereof (such earliest time being herein referred to as
         the "EXPIRATION DATE").

         (b) The Purchase Price for each one one-hundredth of a Preferred Share
upon the exercise of a Right will initially be $20.00, will be subject to
adjustment from time to time as provided in Sections 11 and 13 hereof, and will
be payable in lawful money of the United States of America in accordance with
Section 7(c) hereof (the "PURCHASE PRICE").

         (c) Upon receipt of a Rights Certificate representing exercisable
Rights, with the appropriate 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 Rights Certificate in accordance with Section 9 hereof, in cash or by
certified check, cashier's check, money order, or bank draft paid or payable to
the order of the Company, the Rights Agent will thereupon promptly:

             (i) (A) requisition from any transfer agent of the Preferred Shares
         (or make available, if the Rights Agent is the transfer agent)
         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, in its sole discretion,
         elects to deposit the Preferred Shares issuable upon


<PAGE>
                                      -10-


         conversion of the Rights hereunder into a depository, requisition from
         the depository agent depository 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 will be deposited by the transfer agent with the depository
         agent) and the Company will direct the depository agent to comply with
         such request;

             (ii) when appropriate, requisition from the Company the amount of
         cash, if any, to be paid in lieu of issuance of fractional shares in
         accordance with Section 15 hereof;

             (iii) promptly after receipt of such certificates or depository
         receipts, cause the same to be delivered to or upon the order of the
         registered holder of such Rights Certificate, registered in such name
         or names as may be designated by such holder; and

             (iv) when appropriate, after receipt, promptly deliver such cash to
         or upon the order of the registered holder of such Rights Certificate.
         In the event that the Company is obligated to issue other securities
         of the Company pursuant to Section 11(a), the Company will make all
         arrangements necessary so that such other securities are available for
         distribution by the Rights Agent, if, as, and when appropriate.

         (d) Subject to the provisions of Section 15 hereof, if the registered
holder of any Rights Certificate exercises less than all of the Rights evidenced
thereby, a new Rights Certificate evidencing Rights equivalent to the Rights
remaining unexercised will be issued by the Rights Agent to the registered
holder of such Rights Certificate.

         (e) Notwithstanding anything in this Agreement to the contrary, from
and after the first occurrence of a Section 11(a)(ii) Event, any Rights acquired
or beneficially owned by any:

             (i)  Acquiring Person or Associate or Affiliate of an Acquiring
         Person;

             (ii) transferee of an Acquiring Person (or of any Associate or
         Affiliate of an Acquiring Person) who becomes such a transferee after
         the Acquiring Person becomes such; or

             (iii) transferee of an Acquiring Person (or of any Associate or
         Affiliate of an Acquiring Person) who becomes a transferee prior to
         or concurrently with the Acquiring Person becoming such and who
         receives such Rights pursuant to either (A) a transfer (regardless of
         whether for consideration) from such Acquiring Person, Associate, or
         Affiliate to holders of equity interests in such Acquiring Person,
         Associate, or Affiliate, or to any Person with whom such Acquiring
         Person, Associate, or Affiliate has any continuing oral or written
         plan, agreement, arrangement, or understanding regarding the
         transferred Rights, or (B) a transfer that the Board of Directors of
         the Company has determined is part of an oral or written plan,
         agreement, arrangement, or understanding that has as a primary


<PAGE>
                                      -11-


         purpose or effect avoidance of this Section 7(e);

(each Person described in the preceding clauses (i) through (iii) of this
Section 7(e), a "SECTION 7(e) PERSON") will become null and void without any
further action being required therefor, and no holder of such Rights will have
any rights whatsoever with respect to such Rights, whether under this Agreement
or otherwise.

         The Company will use reasonable efforts to insure that the provisions
of this Section 7(e) and Sections 3(c) and 4 hereof are complied with, but will
have no liability to any holder of Rights Certificates or any other Person as a
result of its failure to make or erroneous making of any determination with
respect to an Acquiring Person, Affiliate or Associate of an Acquiring Person,
or transferee of any such Person.

         (f) Notwithstanding anything in this Agreement to the contrary, neither
the Rights Agent nor the Company will 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 the certificate contained in the form of
election to purchase set forth on the reverse side of the Rights Certificate
surrendered for such exercise will have been properly completed and duly
executed by the registered holder thereof and the Company will have been
provided with such additional evidence of the identity of the Beneficial Owner
(or former Beneficial Owner) or Affiliates or Associates thereof as the Company
may reasonably request.

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

         SECTION 9. RESERVATION AND AVAILABILITY OF PREFERRED SHARES.

         (a) 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, a number of Preferred Shares (or other
securities) sufficient to permit the exercise in full of all outstanding Rights
in accordance with Section 7 of this Agreement.

         (b) The Company covenants and agrees that it will take all such action
as may be necessary to ensure that all Preferred Shares or other securities
delivered upon due exercise of Rights and payment of the purchase price therefor
will be duly and validly authorized and issued, fully paid, and nonassessable at
the time of delivery of the certificates for such Preferred Shares or other
securities.


<PAGE>
                                      -12-


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

         (d) The Company may temporarily suspend the exercisability of the
Rights in order to prepare and file any registration statement as may be
required to be filed pursuant to applicable law with respect to securities
purchasable upon exercise of the Rights. Upon any such suspension, the Company
will issue a public announcement stating that the exercisability of the Rights
has been temporarily suspended. The Company will thereafter issue a public
announcement at such time as the suspension is no longer in effect.

         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 will 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 will be dated, the date upon which the Rights Certificate
evidencing such Rights was duly surrendered 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 will be
deemed to have become the record holder of such shares on, and such certificate
will be dated, the next succeeding Business Day on which the Preferred Shares
(or other securities) transfer books of the Company are open.

         Until a Rights Certificate has been duly exercised, the holder thereof
will not be entitled to any rights of a stockholder of the Company with respect
to shares for which the Rights may be exercisable (including without limitation
the rights to vote and to receive dividends and other distributions) and will
not be entitled to receive any notice of any proceedings of the Company, except
as specifically provided herein.

         SECTION 11. ADJUSTMENT OF PURCHASE PRICE, NUMBER AND KIND OF SHARES OR
NUMBER OF RIGHTS. The Purchase Price, the number and kind of 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) Except as otherwise provided in this Section 11(a) and
         in Section 7(e), if the Company at any time after the date of this
         Agreement (A) declares a dividend on the Preferred Shares payable in
         Preferred Shares, (B) subdivides the outstanding Preferred Shares, (C)
         combines the outstanding


<PAGE>
                                      -13-


         Preferred Shares into a smaller number of shares, or (D) issues 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), then 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, as the case may be, and
         the number and kind of shares of capital stock issuable on such date,
         each will be proportionately adjusted so that the holder of any Right
         duly exercised after such applicable time will be entitled to receive,
         upon payment of the Purchase Price then in effect, the aggregate
         number and kind of shares of capital stock that, if such Right had
         been exercised immediately prior to such applicable time 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 will 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 that would
         require an adjustment under both this Section 11(a)(i) and Section
         11(a)(ii), the adjustment provided for in this Section 11(a)(i) will
         be in addition to, and will be made prior to, any adjustment required
         pursuant to Section 11(a)(ii).

             (ii) Subject to Section 25 of this Agreement, if any Person
         becomes an Acquiring Person then, and in each such case, proper
         provision will be made promptly so that, following the Distribution
         Date, each holder of a Right, except as provided in Section 7(e)
         hereof, will 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 is
         equal to the result obtained by (x) multiplying the then current
         Purchase Price by the number of one one-hundredths of a Preferred Share
         for which a Right was exercisable immediately prior to the first
         occurrence of a Section 11(a)(ii) Event, and (y) dividing that product
         (which following such first occurrence will thereafter be referred to
         as the "PURCHASE PRICE" for each Right and for all purposes of this
         Agreement) by 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 of such first occurrence (such number of shares, the
         "ADJUSTMENT SHARES"); 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 will apply and no adjustment will be made pursuant to
         this Section 11(a)(ii). If 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.

             (iii) If the number of Common Shares that are authorized by the
         Company's certificate of incorporation (as amended and in effect as of
         the relevant time) but not outstanding or reserved for issuance for
         purposes other than upon exercise of the Rights, are not sufficient to
         permit the exercise in full of the Rights


<PAGE>
                                      -14-


         in accordance with the foregoing subparagraph (ii) of this Section
         11(a), the Company shall take all such action as may be necessary to
         authorize additional Common Shares for issuance upon exercise of the
         Rights. If the Company shall, after good faith effort, be unable to
         take all such action as may be necessary to authorize such additional
         Common Shares, the Company shall then 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 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.

         (b) If the Company fixes 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 or more favorable
rights, privileges, and preferences 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 will be determined by multiplying the Purchase Price in effect
immediately prior to such record date by a fraction, the numerator of which will
be the number of Preferred Shares outstanding on such record date plus the
number of Preferred Shares that the aggregate offering price of the total number
of Preferred Shares and/or 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 will 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 will 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 will be in a form other than cash, the
value of such consideration will be as determined in good faith by the Board of
Directors of the Company, whose determination will be described in a statement
filed with the Rights Agent. Preferred Shares owned by or held for the account
of the Company will not be deemed outstanding for the purpose of any such
computation. Such adjustment will 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 will be adjusted to be the Purchase Price which would
then be in effect if such record date had not been fixed.

         (c) If the Company fixes 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 cash, evidences of indebtedness, or other assets
(other than 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 will be determined by


<PAGE>
                                      -15-


multiplying the Purchase Price in effect immediately prior to such record date
by a fraction, the numerator of which will be the then current per share market
price of the Preferred Shares on such record date, less the fair market value
(as determined in good faith by the Board of Directors of the Company, whose
determination will be described in a statement filed with the Rights Agent) of
the portion of the cash, evidences of indebtedness, or other assets so to be
distributed or of such subscription rights or warrants applicable to one
Preferred Share and the denominator of which will be such current per share
market price of the Preferred Shares; PROVIDED, HOWEVER, that in no event will
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 will be made successively whenever
such a record date is fixed; and in the event that such distribution is not so
made, the Purchase Price will again be adjusted to be the Purchase Price that
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 will be deemed to be the average of
         the daily closing prices per share of such Security for the 30
         consecutive Trading Days (as 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 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 will be appropriately
         adjusted to reflect the current market price per share equivalent of
         such Security. The closing price for each day will 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 National Association of Securities Dealers, Inc. (the
         "NASDAQ") National Market System, or if the Security is not listed or
         admitted to trading on the NASDAQ, 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 if the Security is not
         listed or admitted to trading on any national securities exchange, 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 Automated Quotations System 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" means 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


<PAGE>
                                      -16-


         per share market price" of the Preferred Shares will 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" means the
         fair value per share as determined in good faith by the Board of
         Directors of the Company, whose determination will be described in a
         statement filed with the Rights Agent.

         (e) Subject to the final sentence of this Section 11(e), no adjustment
in the Purchase Price will be required unless such adjustment would require an
increase or decrease of at least 1% in the Purchase Price; PROVIDED, HOWEVER,
that any adjustments that by reason of this Section 11(e) are not required to be
made will be carried forward and taken into account in any subsequent
adjustment. All calculations under this Section 11 will be made to the nearest
cent or to the nearest one-millionth 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 will
be made no later than the earlier of (i) three years from the date of the
transaction that requires such adjustment or (ii) the Expiration Date.

         (f) If as a result of an adjustment made pursuant to Section 11(a)
hereof, the holder of any Right thereafter exercised will become entitled to
receive any shares of capital stock of the Company other than Preferred Shares,
thereafter the number of such other shares so receivable upon exercise of any
Right will 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), (e), (h) through (k),
and (m), and the provisions of Sections 7, 9, 10, 13, 14, and 15 with respect to
the Preferred Shares will 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 will 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 has exercised its election as provided in
Section 11(i), upon each adjustment of the Purchase Price as a result of the
calculations made in Sections 11(b) and (c), each Right outstanding immediately
prior to the making of such adjustment will 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 (calculated to the nearest one millionth 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.


<PAGE>
                                      -17-


         (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 will 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 will 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 will 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 Rights Certificates have been
issued, will be at least 10 days later than the date of the public
announcement. If Rights Certificates have been issued, upon each adjustment
of the number of Rights pursuant to this Section 11(i), the Company as
promptly as practicable will cause to be distributed to holders of record of
Rights Certificates on such record date Rights Certificates evidencing,
subject to Section 15 hereof, the additional Rights to which such holders
will be entitled as a result of such adjustment, or at the Company's option,
will cause to be distributed to such holders of record in substitution and
replacement for the Rights Certificates held by such holders prior to the
date of adjustment, and upon surrender thereof, if required by the Company,
new Rights Certificates evidencing all the Rights to which such holders are
entitled after such adjustment. Rights Certificates so to be distributed will
be issued, executed, and countersigned in the manner provided for herein (and
may bear, at the option of the Company, the adjusted Purchase Price) and will
be registered in the names of the holders of record of Rights 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 Rights Certificates theretofore and thereafter
issued may continue to express the Purchase Price and the number of one
one-hundredths of a Preferred Share that were expressed in the initial Rights
Certificates issued hereunder.

         (k) Before taking any action that would cause an adjustment reducing
the Purchase Price below one one-hundredths of the then par value, if any, of
the Preferred Shares issuable upon exercise of the Rights, the Company will
take any corporate action that may be necessary, in the opinion of its
counsel, 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 requires that an adjustment
in the Purchase Price be made effective as of a record date for a specified
event, the Company may 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

<PAGE>
                                      -18-


exercise over and above 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 will deliver to such holder an appropriate instrument
evidencing such holder's right to receive such additional shares upon the
occurrence of the event requiring such adjustment.

         (m) Anything in this Section 11 to the contrary notwithstanding, the
Company will 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 determines 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 that by their terms are
convertible into or exchangeable for Preferred Shares, stock dividends, or
issuance of rights, options, or warrants referred to hereinabove in this Section
11, hereafter made by the Company to holders of its Preferred Shares will not be
taxable to such stockholders.

         (n) If at any time after the date of this Rights 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 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(n)
shall be made successively whenever such a dividend is declared or paid or such
a subdivision, combination or consolidation is effected.

         SECTION 12. CERTIFICATE OF ADJUSTED PURCHASE PRICE OR NUMBER OF SHARES.
Whenever an adjustment is made pursuant to Sections 11 or 13 hereof, the Company
will 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 Rights Certificate (or if prior to the Distribution Date, to each
holder of a certificate representing Preferred Shares) in accordance with
Section 27 hereof. The Rights Agent may rely on such certificate without further
inquiry and may assume that no such adjustment has been made unless and until it
will have received such certificate.

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

         (a) If, following the Shares Acquisition Date, directly or indirectly:

<PAGE>
                                      -19-


             (x) the Company consolidates with, or merges with and into, any
         other Person (other than a Subsidiary of the Company in a transaction
         that complies with Section 14(b) hereof), and the Company is not the
         continuing or surviving corporation of such consolidation or merger;

             (y) any Person (other than a Subsidiary of the Company in a
         transaction that complies with Section 14(b) hereof) consolidates with
         the Company, or merges with and into the Company and the Company is the
         continuing or surviving corporation of such merger, and in connection
         with such merger, all or part of the Common Shares will be changed into
         or exchanged for stock or other securities of any other Person (or the
         Company) or cash or any other property;

             (z) the Company sells or otherwise transfers (or one or more of its
         Subsidiaries sells or otherwise transfers), in one or more
         transactions, assets or earning power aggregating 50% or more of the
         assets or earning power of the Company and its Subsidiaries (taken as
         a whole) to any Person (other than to the Company or one or more of
         its Subsidiaries, in one or more transactions that complies with
         Section 14 hereof);

then, and in each such case, proper provision will be made so that (i) following
the Distribution Date, and subject to Section 7(e) hereof, each holder of a
Right will have the right to receive, upon the exercise thereof at 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 freely
tradable Common Shares of the Principal Party (as hereinafter defined), free and
clear of liens, rights of call or first refusal, encumbrances, and other adverse
claims, as is equal to the result obtained by (1) multiplying the then current
Purchase Price by the number of one one-hundredths of a Preferred Share for
which a Right is exercisable immediately prior to the first occurrence of a
Section 13 Event (or, if a Section 11(a)(ii) Event has occurred prior to the
first occurrence of a Section 13 Event, multiplying the number of such shares
for which a Right was exercisable immediately prior to the first occurrence of a
Section 11(a)(ii) Event, by the Purchase Price in effect immediately prior to
such first occurrence), and (2) dividing that product (which following the first
occurrence of a Section 13 Event, will be referred to as the "PURCHASE PRICE"
for each Right and for all purposes of this Agreement) by 50% of the 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 Section 13
Event; (ii) such Principal Party will thereafter be liable for, and will 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"
will thereafter be deemed to refer to such Principal Party, it being
specifically intended that the provisions of Section 11 hereof will apply to
such Principal Party; and (iv) such Principal Party will take such steps
(including without limitation the reservation of a sufficient number 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 will
thereafter be applicable, as nearly as reasonably may be, in relation to the
Common Shares thereafter deliverable upon the exercise of the Rights.


<PAGE>
                                      -20-


         (b) "PRINCIPAL PARTY" means

             (i) in the case of any transaction described in clause (x) or (y)
         of the first sentence of subsection (a) of this Section 13, the
         Person that is the issuer of any securities into which Common Shares of
         the Company are converted in such merger of 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 clause (z) of
         the first sentence of paragraph (a) of this Section 13, 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 such 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 Securities Exchange Act of l934, as
amended (the "EXCHANGE ACT"), and such Person is a direct or indirect subsidiary
or Affiliate of another Person, then "Principal Party" will 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" will 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 the preceding clauses (1)
and (2) will 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
ventures and the Principal Parties in each such chain will 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 will not consummate any such consolidation, merger,
sale or transfer unless the Principal Party has a sufficient number of
authorized 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 first execute and deliver 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 Section 13 Event, the Principal Party at its own expense will:

             (i) prepare and file a registration statement under the Securities
         Act with respect to the Rights and the securities purchasable upon the
         exercise of the Rights, 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 meeting
         the requirements of the Securities Act) until the Expiration Date;

             (ii) use its best efforts to qualify or register the Rights and the
         securities


<PAGE>
                                      -21-


         purchasable upon exercise of the Rights under the blue sky laws of
         such jurisdictions as may be necessary;

             (iii) use its best efforts to list (or continue the listing of) the
         Rights and the securities purchasable upon exercise of the Rights on a
         national securities exchange or to meet the eligibility requirements
         for quotation on the NASDAQ National Market System; and

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

The provisions of this Section 13 will similarly apply to successive mergers or
consolidations or sales or other transfers. If a Section 13 Event occurs at any
time after the occurrence of a Section 11(a)(ii) Event, the Rights that have not
theretofore been exercised will thereafter become exercisable solely in the
manner described in paragraph (a) of this Section 13.

         SECTION 14. ADDITIONAL COVENANTS.

         (a) The Company covenants and agrees that it will not at any time after
the Distribution Date (i) consolidate with, (ii) merge with or into, or (iii)
sell or 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, if at the time of or after
such consolidation, merger, or sale there are any charter or by-law provisions
or any rights, warrants, or other instruments outstanding or any other action
taken or circumstances extant that would diminish or otherwise eliminate the
benefits intended to be afforded by the Rights. The Company will not consummate
any such consolidation, merger, or sale unless the Company and such other Person
first execute and deliver to the Rights Agent a supplemental agreement
evidencing compliance with this subsection.

         (b) The Company covenants and agrees that, after the Distribution Date,
it will not, except as permitted by Section 24 or Section 28 hereof, take any
action if at the time such action is taken it is reasonably foreseeable that
such action will substantially diminish or otherwise eliminate the benefits
intended to be afforded by the Rights.

         SECTION 15. FRACTIONAL RIGHTS AND FRACTIONAL SHARES.

         (a) The Company will not be required to issue fractions of Rights,
except prior to the Distribution Date as provided in Section 11(i), or to
distribute Rights Certificates that evidence fractional Rights. In lieu of such
fractional Rights, there will be paid to the registered holders of the Rights
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 15(a), the current
market value of a whole Right will 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


<PAGE>
                                      -22-


issuable. The closing price for any day will 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 NASDAQ National Market System, or if the Rights are
not listed or admitted to trading on the NASDAQ National Market System, 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 if the Rights are not listed or
admitted to trading on any national securities exchange, 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 will be used.

         (b) The Company will not be required to issue fractions of Preferred
Shares (other than fractions which are integral multiples of one one-hundredths
of a Preferred Share) upon exercise of the Rights or to distribute certificates
that evidence fractional Preferred Shares (other than fractions which are
integral multiples of one one-hundredths of a Preferred Share). Fractions of
Preferred Shares in integral multiples of one one-hundredths of a Preferred
Share may, at the election of the Company, be evidenced by depositary receipts,
pursuant to an appropriate agreement between the Company and a depositary
selected by it; provided that such agreement shall provide that the holders of
such depositary receipts shall have all the rights, privileges and preferences
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-hundredths of a Preferred Share, the
Company will pay to the registered holders of Rights 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 15(b), the current market value of a Preferred Share will be the
closing price of a Preferred Share (as determined pursuant to Section 11(d)(ii)
hereof) for the Trading Day immediately prior to the date of such exercise.

         (c) 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.

         SECTION 16. RIGHTS OF ACTION. Excepting the rights of action given to
the Rights Agent under Section 19 hereof, all rights of action in respect of
this Agreement are vested in the respective registered holders of the Rights
Certificates (and prior to the Distribution Date, the registered holders of the
Common Shares); and any registered holder of any Rights 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 Rights 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 Rights Certificate in the manner provided
in such Rights Certificate and


<PAGE>
                                      -23-


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 will 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 17. AGREEMENT OF RIGHTS 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;

         (b) after the Distribution Date, the Rights Certificates are
transferable only on the registry books of the Rights Agent if surrendered at
the principal office of the Rights Agent, duly indorsed or accompanied by a
proper instrument of transfer;

         (c) subject to Section 6 and Section 7(f) hereof, the Company and the
Rights Agent may deem and treat the Person in whose name the Rights 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 Rights
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 will be affected by any notice to the contrary;
and

         (d) notwithstanding anything in this Agreement to the contrary, neither
the Company nor the Rights Agent will have any liability to any holder of a
Right or a beneficial interest in a Right or other Person as a result of its
inability to perform any of its obligations under this Agreement by reason of
any preliminary or permanent injunction or other order, decree, or ruling issued
by a court of competent jurisdiction or by a governmental, regulatory, or
administrative agency or commission, or any statute, rule, regulation, or
executive order promulgated or enacted by any governmental authority,
prohibiting or otherwise restraining performance of such obligation; PROVIDED,
HOWEVER, the Company must use its best efforts to have any such order, decree or
ruling lifted or otherwise overturned as soon as possible.

         SECTION 18. RIGHTS CERTIFICATE HOLDER NOT DEEMED A STOCKHOLDER. No
holder, as such, of any Rights Certificate will be entitled to vote, receive
dividends or be deemed for any purpose to be the holder of the Preferred Shares
or any other securities of the Company that may at any time be issuable on the
exercise of the Rights represented thereby, nor will anything contained herein
or in any Rights Certificate be construed to confer upon the holder of any
Rights 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


<PAGE>
                                      -24-


(except as provided in Section 26 hereof), or to receive dividends or
subscription rights, or otherwise, until the Right or Rights evidenced by such
Rights Certificate have been exercised in accordance with the provisions hereof.

         SECTION 19. 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
gross 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 arising directly therefrom.

         The Rights Agent will be protected and will 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 Rights Certificate or
certificate for Common Shares or 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 if necessary,
verified or acknowledged, by the proper Person or Persons.

         SECTION 20. 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 may be a party, or any corporation succeeding to the stock transfer or
corporate trust business of the Rights Agent or any successor Rights Agent, will
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 that such corporation would be eligible for appointment as a
successor Rights Agent under the provisions of Section 22 hereof. In case at the
time such successor Rights Agent succeeds to the agency created by this
Agreement, any of the Rights Certificates will have been countersigned but not
delivered, any such successor Rights Agent may adopt the countersignature of the
predecessor Rights Agent and deliver such Rights Certificates so countersigned;
and in case at that time any of the Rights Certificates have not been
countersigned, any successor Rights Agent may countersign such Rights
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 Rights Certificates
will have the full force provided in the Rights Certificates and in this
Agreement.

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


<PAGE>
                                      -25-


         SECTION 21. 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 Rights Certificates,
by their acceptance thereof, will be bound:

         (a) The Rights Agent may consult with legal counsel (who may be legal
counsel for the Company), and the opinion of such counsel will 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 deems it necessary or desirable that any fact or matter (including
without limitation the identity of any Acquiring Person) 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 is specifically
prescribed herein) may be deemed to be conclusively proved and established by a
certificate signed by the Chief Executive Officer, President, any Vice
President, the Treasurer, or the Secretary of the Company and delivered to the
Rights Agent; and such certificate will 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.

         (c) The Rights Agent will be liable hereunder to the Company and any
other Person only for its own gross negligence, bad faith, or willful
misconduct.

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

         (e) The Rights Agent will 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 Rights Certificate (except its countersignature thereof); nor
will it be responsible for any breach by the Company of any covenant or
condition contained in this Agreement or in any Rights Certificate; nor will it
be responsible for any adjustment required under the provisions of Section 11 or
Section 13 hereof or for the manner, method, or amount of any adjustment or the
ascertaining of the existence of facts that would require any such adjustment
(except with respect to the exercise of Rights evidenced by Rights Certificates
after receipt of a certificate furnished pursuant to Section 12 describing any
such adjustment); nor will it be responsible for any determination by the Board
of Directors of the Company of the current market value of the Rights, Common
Shares or Preferred Shares; nor will it by any act hereunder be deemed to make
any representation or warranty as to the authorization or reservation of any
Preferred Shares, Common Shares or other securities to be issued pursuant to
this Agreement or any Rights Certificate or as to whether any Preferred Shares,
Common Shares or other securities will, when issued, be validly authorized and
issued, fully paid, and nonassessable.


<PAGE>
                                      -26-


         (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 the
Chief Executive Officer, President, any Vice President, the Treasurer, or the
Secretary of the Company, and to apply to such officers for advice or
instructions in connection with its duties, and it will 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 under this Rights
Agreement and the date on and/or after which such action will be taken or such
omission will be effective. The Rights Agent will not be liable for any action
taken by, or omission of, the Rights Agent in accordance with a proposal
included in any such application on or after the date specified in such
application (which date will not be less than ten (10) Business Days after the
date the Chief Executive Officer, President, any Vice President, the Treasurer,
or the Secretary of the Company actually receives such application, unless any
such officer of the Company consents in writing to an earlier date) unless,
prior to taking any such action (or the effective date in the case of an
omission), the Rights Agent receives written instructions in response to such
application specifying the action to be taken or omitted.

         (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 will 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 will 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 the act, default,
neglect, or misconduct of any such attorney or agent, provided reasonable care
was exercised in the selection and continued employment thereof.

         (j) No provision of this Agreement will 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 will 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 Rights Certificate surrendered to the Rights
Agent for exercise or transfer, the certification attached to the form of
assignment or form of election


<PAGE>
                                      -27-


to purchase, as the case may be, has either not been completed or indicates an
affirmative response to clause l and/or 2 thereof, the Rights Agent will not
take any further action with respect to such requested exercise of transfer
without first consulting with the Company.

         SECTION 22. 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' prior notice in writing to the Company and to each transfer agent
of the Common Shares or Preferred Shares in accordance with Section 27 hereof,
and to the holders of the Rights Certificates by first-class mail at the expense
of the Company.

         The Company may remove the Rights Agent or any successor Rights Agent
upon 30 days' prior notice in writing sent to the Rights Agent or successor
Rights Agent, as the case may be, and each transfer agent of the Common Shares
or Preferred Shares in accordance with Section 27 hereof, and to the holders of
the Rights Certificates by first-class mail.

         If the Rights Agent resigns or is removed or otherwise becomes
incapable of acting, the Company will appoint a successor to the Rights Agent.
If the Company fails 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 Rights Certificate (who will, with such notice, submit his
Rights Certificate for inspection by the Company), then the registered holder of
any Rights 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 a
court, will be an entity organized and doing business under the laws of the
United States or any state of the United States (so long as such entity is in
good standing), and 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 $100 million. After
appointment, the successor Rights Agent will 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 will 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 will file notice thereof in writing with the
predecessor Rights Agent and each transfer agent of the Common Shares or
Preferred Shares, and mail a notice thereof in writing to the registered holders
of the Rights Certificates. Failure to give any notice provided for in this
Section 22, however, or any defect therein, will 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 23. ISSUANCE OF NEW RIGHTS CERTIFICATES. Notwithstanding any of
the provisions of this Agreement or of the Rights to the contrary, the Company
at its option may issue new Rights Certificates 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 Rights Certificates made in accordance with the provisions
of this Agreement.


<PAGE>
                                      -28-



         SECTION 24. REDEMPTION.

         (a) The Rights may be redeemed by action of the Board of Directors
pursuant to paragraph (b) of this Section 24, and will not be redeemed in any
other manner.

         (b) The Board of Directors of the Company may, at its option, at any
time prior to the earliest of (x) the close of business on the tenth day
following a Shares Acquisition Date, or (y) 5:00 p.m., E.S.T., on the Final
Expiration Date, redeem all but not less than all of the then outstanding Rights
at a redemption price of $0.0001 per Right, appropriately adjusted to reflect
any stock split, stock dividend or similar transaction occurring after the date
hereof. The redemption of the Rights by the Board of Directors may be made
effective at such time, on such basis, and with such conditions as the Board of
Directors in its sole discretion may establish.

         (c) Immediately upon the action of the Board of Directors of the
Company ordering the redemption of the Rights pursuant to paragraph (b) of this
Section 24, 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 will be to receive the Redemption Price. The Company will promptly
give public notice of any such redemption; PROVIDED, HOWEVER, that the failure
to give, or any defect in, any such notice will not affect the validity of such
redemption. Within 10 days after such action ordering the redemption of the
Rights pursuant to paragraph (b) or (c), as the case may be, the Company will
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 mailed in the manner herein provided will be
deemed duly 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. The Company may, at its option, pay the
Redemption Price in cash, Common Shares (based on the current per share market
price of the Common Shares as of the time of redemption) or any other form of
consideration deemed appropriate by the Board of Directors. Notwithstanding
anything contained in this Agreement to the contrary, the Rights will not be
exercisable after the first occurrence of a Section 11(a)(ii) Event until such
time as the Company's right of redemption under Section 24(b) has expired.

         SECTION 25. EXCHANGE.

         (a) The Company's Board of Directors, at its option, at any time after
the occurrence of a Section 11(a)(ii) Event may exchange all or part of the then
outstanding and exercisable Rights (which will not include Rights that have
become void pursuant to the provisions of Section 7(e) 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 Company's Board of
Directors may not 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


<PAGE>
                                      -29-


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 Company's Board of Directors
ordering the exchange of any Rights pursuant to subsection (a) of this Section
25, and without any further action and without any notice, the right to exercise
such Rights will terminate and the only right thereafter of a holder of such
Rights will 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
will promptly give public notice of any such exchange; PROVIDED, HOWEVER, that
the failure to give, or any defect in, such notice will not affect the validity
of such exchange. The Company promptly will 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 will 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 that will be exchanged. Any partial
exchange will be effected PRO RATA based on the number of Rights (other than
Rights that have become void pursuant to the provisions of Section 7(e) hereof)
held by each holder of Rights.

         (c) If there are not sufficient Common Shares issued but not
outstanding or authorized but unissued to permit any exchange of Rights as
contemplated in accordance with this Section 25, the Company will take all such
action as may be necessary to authorize additional Common Shares for issuance
upon exchange of the Rights. If the Company shall, after 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 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.

         (d) The Company will not be required to issue fractions of Common
Shares or to distribute certificates that evidence fractional Common Shares. In
lieu of such fractional Common Shares, the Company will pay to the registered
holders of the Rights 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
paragraph (e), the current market value of a whole Common Share will be the
closing price of a Common Share (as determined pursuant to Section 11(d)(i)
hereof) for the Trading Day immediately prior to the date of exchange pursuant
to this Section 25.

         SECTION 26. NOTICE OF CERTAIN EVENTS.

         (a) In case the Company proposes, at any time after the Distribution
Date, (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, (ii) to offer to the holders of its Preferred Shares rights or
warrants to subscribe for or to purchase any


<PAGE>
                                      -30-


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 will give to each holder of a Rights
Certificate, in accordance with Section 27 hereof, a notice of such proposed
action, which will specify the record date for the purposes 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 Preferred Shares, if any such
date is to be fixed, and such notice will 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 Preferred Shares, whichever will be the
earlier.

         (b) If a Section 11(a)(ii) Event shall occur, (i) the Company will as
soon as practicable thereafter give to each holder of a Rights Certificate, in
accordance with Section 27 hereof, a notice of the occurrence of such event,
which notice will describe such event and the consequences of such event to
holders of Rights under Section 11(a)(ii) hereof, and (ii) all references in the
preceding paragraph to Common Shares will be deemed thereafter to refer to
Preferred Shares or, if appropriate, other securities.

         SECTION 27. NOTICES. Any notice or demand authorized by this Agreement
to be given or made by the Rights Agent or by the holder of any Rights
Certificate to or on the Company will be sufficiently given or made if sent by
reputable overnight courier or by registered, certified, or first-class mail,
postage or delivery charges prepaid and addressed (until another address is
filed in writing with the Rights Agent) as follows:

                  Cubist Pharmaceuticals, Inc.
                  14 Emily Street
                  Cambridge, Massachusetts  02148
                  Attn: President and CEO

         Any notice or demand authorized by this Agreement to be given or made
by the Company or by the holder of any Rights Certificate to or on the Rights
Agent will be sufficiently given or made if sent by reputable overnight courier
or by registered, certified, or first-class mail, postage or delivery charges
prepaid and addressed (until another address is filed in writing with the
Company) as follows:

                  BankBoston, N.A.


<PAGE>
                                      -31-


                  c/o Equiserve Limited Partnership
                  150 Royall Street
                  Canton, Massachusetts  02021
                  Attn:  Client Administration

Notices or demands authorized by this Agreement to be given or made by the
Company or the Rights Agent to the holder of any Rights Certificate or
certificate representing Common Shares or Preferred Shares will 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 28. SUPPLEMENTS AND AMENDMENTS. Prior to the Distribution Date,
if the Company so directs, the Company and the Rights Agent will supplement or
amend any provision of this Agreement without the approval of any holders of
certificates representing Preferred Shares. From and after the Distribution
Date, if the Company so directs, the Company and the Rights Agent will
supplement or amend this Agreement without the approval of any holders of Rights
Certificates in order (i) to cure any ambiguity, (ii) to correct or supplement
any provision contained herein that may be defective or inconsistent with any
other provisions herein, (iii) to shorten or lengthen any time period hereunder,
or (iv) to change or supplement the provisions hereunder in any manner that the
Company may deem necessary or desirable and that will not adversely affect the
interests of the holders of Rights Certificates (other than an Acquiring Person
or any Affiliate or Associate of an Acquiring Person).

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

         SECTION 30. BENEFITS OF THIS AGREEMENT. Nothing in this Agreement will
be construed to give to any Person or corporation other than the Company, the
Rights Agent and the registered holders of the Rights Certificates (and prior to
the Distribution Date, of the Common Shares) any legal or equitable right,
remedy or claim under this Agreement; but this Agreement will be for the sole
and exclusive benefit of the Company, the Rights Agent, and the registered
holders of the Rights Certificates (and, prior to the Distribution Date, of 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 will remain in
full force and effect and will in no way be affected, impaired or invalidated.

         SECTION 32. GOVERNING LAW. This Agreement and each Rights Certificate
issued hereunder will be deemed to be a contract made under the laws of the
State of Delaware and for all purposes will 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


<PAGE>
                                      -32-


counterparts and each of such counterparts will for all purposes be deemed to be
an original, and all such counterparts will together constitute but one and the
same agreement.

         SECTION 34. DESCRIPTIVE HEADINGS. Descriptive headings of the several
Sections of this Agreement are inserted for convenience only and will not
control or affect the meaning or construction of any of the provisions hereof.



         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed and attested, as an agreement under seal, as of the date first
above written.

                                                 CUBIST PHARMACEUTICALS, INC.



                                                 By:    /s/ Thomas A. Shea
                                                        ----------------------
                                                 Name:  Thomas A. Shea
                                                 Title: CFO



                                                 BANKBOSTON, N.A.,
                                                 as Rights Agent



                                                 By:    /s/ Carol Mulvey-Eori
                                                        ----------------------
                                                 Name:  Carol Mulvey-Eori
                                                 Title: Administration Manager


<PAGE>



                                                                       EXHIBIT A

                                      FORM

                                       of

                           CERTIFICATE OF DESIGNATIONS

                                       of

                  SERIES A JUNIOR PARTICIPATING PREFERRED STOCK

                                       of

                          CUBIST PHARMACEUTICALS, INC.

                         (Pursuant to Section 151 of the
                        Delaware General Corporation Law)

                  Cubist Pharmaceuticals, Inc., a corporation organized and
existing under the General Corporation Law (the "DGCL") of the State of Delaware
(hereinafter called the "CORPORATION"), hereby certifies that the following
resolution was adopted by the Board of Directors of the Corporation as required
by Section 151 of the DGCL at a meeting duly called and held on July 21, 1999:


RESOLVED:                That pursuant to Section 4 of Article IV of the
                         Certificate of Incorporation, as amended, of the
                         Corporation, the Board of Directors hereby
                         establishes a series of Preferred Stock, par value
                         $0.001 per share (the "SERIES A PREFERRED STOCK"), of
                         the Corporation and hereby states the designation and
                         number of shares, and fixes the preferences, voting
                         powers, qualifications and special or relative rights
                         or privileges thereof, as follows:


                  Series A Junior Participating Preferred Stock:

                  Section 1. Designation and Amount. The shares of such series
shall be designated as "Series A Junior Participating Preferred Stock" (the
"SERIES A PREFERRED STOCK") and the number of shares constituting the Series A
Preferred Stock shall be 500,000. Such number of shares may be increased or
decreased by resolution of the Board of Directors; PROVIDED that no decrease
shall reduce the number of shares of Series A Preferred Stock to a number less
than the number of shares of Series A Preferred Stock then outstanding, PLUS the
number of shares reserved for issuance upon the exercise of outstanding options,
rights or warrants or upon conversion of any outstanding securities issued by
the Corporation and convertible into Series A Preferred Stock.

                  Section 2. Dividends and Distributions.

                  (A) Subject to the rights of the holders of any shares of any
         series of Preferred Stock (or any similar stock) ranking prior and
         superior to the Series A


<PAGE>
                                      -2-


         Preferred Stock with respect to dividends, the holders of shares of
         Series A Preferred Stock, in preference to the holders of the Common
         Stock of the Corporation, par value $0.001 per share ("COMMON STOCK"),
         and of any other junior stock, shall be entitled to receive, when, as
         and if declared by the Board of Directors out of funds legally
         available for the purpose, quarterly dividends payable in cash on the
         first day of March, June, September and December in each year (each
         such date being referred to herein as a "QUARTERLY DIVIDEND PAYMENT
         DATE"), commencing on the first Quarterly Dividend Payment Date after
         the first issuance of a share or fraction of a share of Series A
         Preferred Stock, in an amount per share (rounded to the nearest cent)
         equal to the greater of (a) $1 or (b) subject to the provision for
         adjustment hereinafter set forth, 100 times the aggregate per share
         amount of all cash dividends, and 100 times the aggregate per share
         amount (payable in kind) of all non-cash dividends or other
         distributions, other than a dividend payable in shares of Common Stock
         or a subdivision of the outstanding shares of Common Stock (by
         reclassification or otherwise), declared on the Common Stock since the
         immediately preceding Quarterly Dividend Payment Date or, with respect
         to the first Quarterly Dividend Payment Date, since the first issuance
         of any share or fraction of a share of Series A Preferred Stock. In
         the event the Corporation shall at any time declare or pay any
         dividend on the Common Stock payable in shares of Common Stock, or
         effect a subdivision or combination or consolidation of the
         outstanding shares of Common Stock (by reclassification or otherwise
         than by payment of a dividend in shares of Common Stock) into a
         greater or lesser number of shares of Common Stock, then in each such
         case the amount to which holders of shares of Series A Preferred Stock
         were entitled immediately prior to such event under clause (b) of the
         preceding sentence shall be adjusted by multiplying such amount by a
         fraction, the numerator of which is the number of shares of Common
         Stock outstanding immediately after such event and the denominator of
         which is the number of shares of Common Stock that were outstanding
         immediately prior to such event.

           (B) The Corporation shall declare a dividend or distribution on the
         Series A Preferred Stock as provided in paragraph (A) of this Section
         immediately after it declares a dividend or distribution on the Common
         Stock (other than a dividend payable in shares of Common Stock);
         provided that, in the event no dividend or distribution shall have
         been declared on the Common Stock during the period between any
         Quarterly Dividend Payment Date and the next subsequent Quarterly
         Dividend Payment Date, a dividend of $1 per share on the Series A
         Preferred Stock shall nevertheless be payable on such subsequent
         Quarterly Dividend Payment Date.

           (C) Dividends shall begin to accrue and be cumulative on outstanding
         shares of Series A Preferred Stock from the Quarterly Dividend Payment
         Date next preceding the date of issue of such shares, unless the date
         of issue of such shares is prior to the record date for the first
         Quarterly Dividend Payment Date, in which case dividends on such
         shares shall begin to accrue from the date of issue of such shares, or
         unless the date of issue is a Quarterly Dividend Payment Date or is a
         date after the record date for the determination of holders of shares
         of Series A Preferred Stock entitled to receive a quarterly dividend
         and before such Quarterly


<PAGE>
                                      -3-


         Dividend Payment Date, in either of which events such dividends shall
         begin to accrue and be cumulative from such Quarterly Dividend Payment
         Date. Accrued but unpaid dividends shall not bear interest. Dividends
         paid on the shares of Series A Preferred Stock in an amount less than
         the total amount of such dividends at the time accrued and payable on
         such shares shall be allocated pro rata on a share-by-share basis
         among all such shares at the time outstanding. The Board of Directors
         may fix a record date for the determination of holders of shares of
         Series A Preferred Stock entitled to receive payment of a dividend or
         distribution declared thereon, which record date shall be not more
         than 60 days prior to the date fixed for the payment thereof.

           Section 3. Voting Rights. The holders of shares of Series A Preferred
Stock shall have the following voting rights:

           (A) Subject to the provision for adjustment hereinafter set forth,
         each share of Series A Preferred Stock shall entitle the holder
         thereof to 100 votes on all matters submitted to a vote of the
         stockholders of the Corporation. In the event the Corporation shall at
         any time declare or pay any dividend on the Common stock payable in
         shares of Common Stock, or effect a subdivision or combination or
         consolidation of the outstanding shares of Common Stock (by
         reclassification or otherwise than by payment of a dividend in shares
         of Common Stock) into a greater or lesser number of shares of Common
         Stock, then in each such case the number of votes per share to which
         holders of shares of Series A Preferred Stock were entitled
         immediately prior to such event shall be adjusted by multiplying such
         number by a fraction, the numerator of which is the number of shares
         of Common Stock outstanding immediately after such event and the
         denominator of which is the number of shares of Common Stock that were
         outstanding immediately prior to such event.

           (B) Except as otherwise provided herein, in any other Certificate of
         Designations creating a series of Preferred Stock or any similar stock,
         or by law, the holders of shares of Series A Preferred Stock and the
         holders, of shares of Common Stock and any other capital stock of the
         Corporation having general voting rights shall vote together as one
         class on all matters submitted to a vote of stockholders of the
         Corporation.

           (C) Except as set forth herein, or as otherwise provided by law,
         holders of Series A Preferred Stock shall have no special voting
         rights and their consent shall not be required (except to the extent
         they are entitled to vote with holders of Common Stock as set forth
         herein) for taking any corporate action.

           Section 4. Certain Restrictions.

           (A) Whenever quarterly dividends or other dividends or distributions
         payable on the Series A Preferred Stock as provided in Section 2 are
         in arrears, thereafter and until all accrued and unpaid dividends and
         distributions, whether or not declared, on shares of Series A
         Preferred Stock outstanding shall have been paid in full, the
         Corporation shall not:


<PAGE>
                                      -4-


             (i) declare or pay dividends, or make any other distributions, on
         any shares of stock ranking junior (either as to
         dividends or upon liquidation, dissolution or winding up) to the Series
         A Preferred Stock;

             (ii) declare or pay dividends, or make any other distributions, on
         any shares of stock ranking on a parity (either as to dividends or
         upon liquidation, dissolution or winding up) with the Series A
         Preferred Stock, except dividends paid ratably on the Series A
         Preferred Stock and all such parity stock on which dividends are
         payable or in arrears in proportion to the total amounts to which the
         holders of all such shares are then entitled;

             (iii) redeem or purchase or otherwise acquire for consideration
         shares of any stock ranking junior (either as to dividends or upon
         liquidation, dissolution or winding up) to the Series A Preferred
         Stock, provided that the Corporation may at any time redeem, purchase
         or otherwise acquire shares of any such junior stock in exchange for
         shares of any stock of the Corporation ranking junior (either as to
         dividends or upon dissolution, liquidation or winding up) to the
         Series A Preferred Stock; or

             (iv) redeem or purchase or otherwise acquire for consideration any
         shares of Series A Preferred Stock, or any shares of stock ranking on
         a parity with the Series A Preferred Stock, except in accordance with
         a purchase offer made in writing or by publication (as determined by
         the Board of Directors) to all holders of such shares upon such terms
         as the Board of Directors, after consideration of the respective
         annual dividend rates and other relative rights and preferences of the
         respective series and classes, shall determine in good faith will
         result in fair and equitable treatment among the respective series or
         classes.

           (B) The Corporation shall not permit any subsidiary of the
         Corporation to purchase or otherwise acquire for consideration any
         shares of stock of the Corporation unless the Corporation could, under
         paragraph (A) of this Section 4, purchase or otherwise acquire such
         shares at such time and in such manner.

           Section 5. Reacquired Shares. Any shares of Series A Preferred
Stock purchased or otherwise acquired by the Corporation in any manner
whatsoever shall be retired and canceled promptly after the acquisition thereof.
All such shares shall upon their cancellation become authorized but unissued
shares of Preferred Stock and may be reissued as part of a new series of
Preferred Stock subject to the conditions and restrictions on issuance set forth
herein, in the Certificate of Incorporation, or in any other Certificate of
Designations creating a series of Preferred Stock or any similar stock or as
otherwise required by law.

           Section 6. Liquidation, Dissolution or Winding Up. Upon any
liquidation, dissolution or winding up of the Corporation, no distribution shall
be made (1) to the holders of shares of stock ranking junior (either as to
dividends or upon liquidation, dissolution or winding up) to the Series A
Preferred Stock unless, prior thereto, the holders of shares of Series A
Preferred Stock shall have received $100 per share, plus an amount equal to
accrued and unpaid dividends and distributions thereon, whether or not declared,
to the date of such payment, provided that the holders of shares of Series A
Preferred Stock


<PAGE>
                                      -5-


shall be entitled to receive an aggregate amount per share, subject to the
provision for adjustment hereinafter set forth, equal to 100 times the aggregate
amount to be distributed per share to holders of shares of Common Stock, or (2)
to the holders of shares of stock ranking on a parity (either as to dividends or
upon liquidation, dissolution or winding up) with the Series A Preferred Stock,
except distributions made ratably on the Series A Preferred Stock and all such
parity stock in proportion to the total amounts to which the holders of all such
shares are entitled upon such liquidation, dissolution or winding up. In the
event the Corporation shall at any time declare or pay any dividend on the
Common Stock payable in shares of Common Stock, or effect a subdivision or
combination or consolidation of the outstanding shares of Common Stock (by
reclassification or otherwise than by payment of a dividend in shares of Common
Stock) into a greater or lesser number of shares of Common Stock, then in each
such case the aggregate amount to which holders of shares of Series A Preferred
Stock were entitled immediately prior to such event under the proviso in clause
(1) of the preceding sentence shall be adjusted by multiplying such amount by a
fraction the numerator of which is the number of shares of Common Stock
outstanding immediately after such event and the denominator of which is the
number of shares of Common Stock that were outstanding immediately prior to such
event.

           Section 7. Consolidation, Merger, etc. In case the Corporation shall
enter into any consolidation, merger, combination or other transaction in which
the shares of Common Stock are exchanged for or changed into other stock or
securities, cash and/or any other property, then in any such case each share of
Series A Preferred Stock shall at the same time be similarly exchanged or
changed into an amount per share, subject to the provision for adjustment
hereinafter set forth, equal to 100 times the aggregate amount of stock
securities, cash and/or any other property (payable in kind), as the case may
be, into which or for which each share of Common Stock is changed or exchanged.
In the event the Corporation shall at any time declare or pay any dividend on
the Common Stock payable in shares of Common Stock, or effect a subdivision or
combination or consolidation of the outstanding shares of Common Stock (by
reclassification or otherwise than by payment of a dividend in shares of Common
Stock) into a greater or lesser number of shares of Common Stock, then in each
such case the amount set forth in the preceding sentence with respect to the
exchange or change of shares of Series A Preferred Stock shall be adjusted by
multiplying such amount by a fraction, the numerator of which is the number of
shares of Common Stock outstanding immediately after such event and the
denominator of which is the number of shares of Common Stock that were
outstanding immediately prior to such event.

           Section 8. No Redemption. The shares of Series A Preferred Stock
shall not be redeemable.

           Section 9. Rank. The Series A Preferred Stock shall rank, with
respect to the payment of dividends and the distribution of assets, junior to
all series of any other class of the Corporation's Preferred Stock.

           Section 10. Amendment. The Certificate of Incorporation of the
Corporation shall not be amended in any manner which would materially alter or
change the powers, preferences or special rights of the Series A Preferred Stock
so as to affect them adversely


<PAGE>
                                      -6-


without the affirmative vote of the holders of at least two-thirds of the
outstanding shares of Series A Preferred Stock, voting together as a single
class.

                  IN WITNESS WHEREOF, this Certificate of Designations is
executed on behalf of the Corporation by its Chief Executive Officer and
attested by its Secretary as of           , 1999.
                                ----------

ATTEST:

                                                       By:
                                                            --------------------
                                                       Name:  Justin P. Morreale
                                                       Title: Secretary


<PAGE>


                                                                       EXHIBIT B





                          [FORM OF RIGHTS CERTIFICATE]




CERTIFICATE NO. R-                                                       RIGHTS
                  -------                                        --------


         NOT EXERCISABLE AFTER AUGUST 3, 2009, OR EARLIER IF NOTICE OF
         REDEMPTION OR EXCHANGE OCCURS. THE RIGHTS ARE SUBJECT, AT THE OPTION OF
         THE COMPANY, TO REDEMPTION AT $0.0001 PER RIGHT AND TO EXCHANGE ON THE
         TERMS SET FORTH IN THE RIGHTS AGREEMENT. UNDER CERTAIN CIRCUMSTANCES,
         RIGHTS BENEFICIALLY OWNED BY AN ACQUIRING PERSON (AS SUCH TERM IS
         DEFINED IN THE RIGHTS AGREEMENT) AND ANY SUBSEQUENT HOLDER OF SUCH
         RIGHTS MAY BECOME NULL AND VOID.


                               RIGHTS CERTIFICATE

                          CUBIST PHARMACEUTICALS, 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 April 30, 1999 (the "RIGHTS AGREEMENT"), by and
between Cubist Pharmaceuticals, Inc. (the "COMPANY"), a Delaware corporation,
and BankBoston, N.A. (the "RIGHTS AGENT"), to purchase from the Company at any
time after the Distribution Date (as defined in the Rights Agreement) and prior
to 5:00 P.M., Boston time, on August 3, 2009, at the office of the Rights Agent
designated for such purpose, or at the office of its successor as Rights Agent
designated for such purpose, one one-hundredth of a share of the Series A Junior
Participating Preferred Stock, par value $0.001 per share (the "PREFERRED
SHARES"), of the Company, at a purchase price of $20.00 per one one-hundredth of
a Preferred Share (the "PURCHASE PRICE"), upon presentation and surrender of
this Rights Certificate with the Form of Election to Purchase duly executed. The
number of Rights evidenced by this Rights Certificate (and the number of one
one-hundredths of a


<PAGE>
                                      -2-


Preferred Share that may be purchased upon exercise hereof) set forth above, and
the Purchase Price set forth above, are the number of Rights and Purchase Price
as of August 3***, 1999, based on the Preferred Shares as constituted at such
date. As provided in the Rights Agreement, the Purchase Price and the number of
one one-hundredths of a Preferred Share that may be purchased upon the exercise
of the Rights evidenced by this Rights Certificate are subject to modification
and adjustment upon the happening of certain events.

         This Rights Certificate is subject to all of the terms, provisions, and
conditions of the Rights Agreement, 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 of the Rights Agent,
the Company and the holders of the Rights Certificates. Copies of the Rights
Agreement are on file at the principal executive offices of the Company and the
above-mentioned office of the Rights Agent.

         This Rights Certificate, with or without other Rights Certificates, may
be surrendered at the principal office of the Rights Agent in exchange for
another Rights Certificate or Rights Certificates of like tenor and date
evidencing Rights entitling the holder to purchase the same aggregate number of
one one-hundredths of a Preferred Share as the Rights evidenced by the Rights
Certificate or Rights Certificates surrendered entitled such holder to purchase.
If this Rights Certificate is exercised in part, the holder will be entitled to
receive upon surrender hereof another Rights Certificate or Rights 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 its option at a
redemption price of $0.0001 per Right, or (ii) may be exchanged in whole or in
part by the Company, at its option, for the appropriate number of one
one-hundredths of a Preferred Share.

         Fractional Preferred Shares will be issued upon the exercise of any
Right or Rights evidenced hereby.

         No holder of this Rights Certificate, as such, will be entitled to vote
or receive dividends or be deemed for any purpose the holder of any Preferred
Shares or of any other securities of the Company that may at any time be
issuable on the exercise hereof, nor will 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


<PAGE>
                                      -3-


or subscription rights, or otherwise, until the Right or Rights evidenced by
this Rights Certificate have been exercised as provided in the Rights Agreement.

         This Rights Certificate will not be valid or obligatory for any purpose
until it is countersigned by the Rights Agent.

         Dated as of             ,    .
                     ------------  ----

                                                    CUBIST PHARMACEUTICALS, INC.



                                                    By:
                                                       -----------------------
                                                    Name:
                                                    Title:



Countersigned:

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

By:
   --------------------------
Name:
Title:


<PAGE>
                                      -4-


                  [Form of Reverse Side of Rights Certificate]

                               FORM OF ASSIGNMENT

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


         FOR VALUE RECEIVED
                           ----------------------------------------------------
hereby sells, assigns, and transfers to
                                       ----------------------------------------
- -------------------------------------------------------------------------------

                  (Please print name and address of transferee)

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

this Rights Certificate, together with all right, title, and interest therein,
and does hereby irrevocably constitute and appoint                      as
                                                   ---------------------
attorney, to transfer the within Rights Certificate on the books of Cubist
Pharmaceuticals, Inc., with full power of substitution.

Dated:              ,
       -------------  -----                           -------------------------
                                                             (Signature)

Medallion Signature Guaranty:


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


                            ASSIGNMENT CERTIFICATION

    The undersigned hereby certifies by checking the appropriate boxes that:

    (l) The Rights evidenced by this Rights Certificate [ ] are [ ] are not
being sold, assigned, and transferred by or on behalf of a Person who is or was
an Acquiring Person or an Affiliate or Associate of any such Acquiring Person
(as such term is defined pursuant to the Rate Agreement);

    (2) After due inquiry and to the best knowledge of the undersigned, he, she,
or it [ ] did [ ] did not acquire the Rights evidenced by this Rights
Certificate from any person who is or was an Acquiring Person or an Affiliate or
Associate of an Acquiring Person.

Dated:              ,
       -------------  ------                           ------------------------
                                                             (Signature)


<PAGE>
                                      -5-


                                     NOTICE

         The signatures to the foregoing Assignment and Certification must
correspond exactly to the name of the registered owner hereof, as written upon
the face of this Rights Certificate, without any change whatsoever.

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

                          FORM OF ELECTION TO PURCHASE

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


To CUBIST PHARMACEUTICALS, INC.:

         The undersigned hereby irrevocably elects to exercise
                                                                ----------------
Rights represented by this Rights Certificate to purchase the Preferred Shares
(or fractions thereof or such other securities of the Company or of any other
person) issuable upon the exercise of such Rights and requests that certificates
for such shares be issued in the name of:

Please insert social security
or other identifying number:
                            -----------------------------

- -------------------------------------------------------------------------------
                         (Please print name and address)

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


         (If the above number of Rights is not all of the Rights evidenced by
this Rights Certificate, then a new Rights Certificate for the balance remaining
of such Rights will be registered and returned to the undersigned.)


Dated:               ,
       -------------   -----                             ----------------------
                                                              (Signature)

Medallion Signature Guaranty:

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

                             ELECTION CERTIFICATION

         The undersigned hereby certifies by checking the appropriate boxes
that:


<PAGE>
                                      -6-


         (1) The Rights evidenced by this Rights Certificate [ ] are [ ] are not
being sold, assigned, and transferred by or on behalf of a Person who is or was
an Acquiring Person or an Affiliate or Associate of any Acquiring Person (as
such terms are defined pursuant to the Rate Agreement).

         (2) After due inquiry and to the best knowledge of the undersigned, he,
she, or it [ ] did [ ] did not acquire the Rights evidenced by this Rights
Certificate from any person who is or was an Acquiring Person or an Affiliate or
Associate of any Acquiring Person.



Dated:              ,
       -------------  -----                           -------------------------
                                                           (Signature)

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

                                     NOTICE

         The signatures in the foregoing Election to Purchase and Certification
must correspond exactly to the name of the registered owner hereof, as written
upon the face of this Rights Certificate, without any change whatsoever.

         In the event the certification set forth above in the Assignment or the
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
Rights 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.


<PAGE>



                                                                       EXHIBIT C


                                SUMMARY OF RIGHTS


         On July 21, 1999, the Board of Directors of Cubist Pharmaceuticals,
Inc. (the "COMPANY") declared a dividend of one fractional preferred share
purchase right (a "RIGHT") for each outstanding share of common stock, par value
$0.001 per share (the "COMMON SHARES"), of the Company. The dividend is payable
on August 3, 1999 (the "RECORD DATE") to the stockholders of record on that
date. Except as described below, each Right, when exercisable, entitles the
registered holder to purchase from the Company one one-hundredth of a share of
Series A Junior Participating Preferred Stock of the Company, par value $0.001
per share (the "PREFERRED SHARES"), at a price of $20.00 per one one-hundredth
of a Preferred Share (the "PURCHASE PRICE"), subject to adjustment or
substitution of other securities of the Company in place of the Preferred
Shares. The description and terms of the Rights are set forth in a Rights
Agreement (the "RIGHTS AGREEMENT") between the Company and BankBoston, N.A., as
Rights Agent (the "RIGHTS AGENT").

         Initially, the Rights will be attached to all certificates representing
Common Shares then outstanding, and no separate Rights certificates will be
distributed. Until the earlier to occur of (i) 10 business days following a
public announcement that a person or group of affiliated or associated persons
(an "ACQUIRING PERSON") have acquired beneficial ownership of 15% or more of the
outstanding Common Shares (the date of such an announcement being a "SHARES
ACQUISITION DATE"), 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
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
such outstanding Common Shares (in either case, (i) or (ii), 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
certificates together with a copy of this Summary of Rights.

         The Rights Agreement provides that, until the Distribution Date, 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 for transfer of any certificates for
Common Shares outstanding as of the Record Date, even without such notation or a
copy of this Summary of Rights being attached thereto, 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 ("RIGHTS CERTIFICATES") will be mailed to
holders of record of the Common Shares as of the close of business on the
Distribution Date, and the separate Rights Certificates alone will evidence the
Rights.


<PAGE>
                                      -2-


         The Rights are not exercisable until the Distribution Date. The Rights
will expire on August 3, 2009 (the "FINAL EXPIRATION DATE"), unless the Rights
are earlier redeemed by the Company, 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 $1 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.

         If, after the first date of public announcement by the Company or an
Acquiring Person that an Acquiring Person has become such, the Company is
involved in a merger or other business combination transaction in which the
Common Shares are exchanged or changed, or 50% or more of the Company's
consolidated assets or earning power are sold (in one transaction or a series of
transactions), proper provision will be made so that each holder of a Right
(other than an Acquiring Person) 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 (or, in the event
there is more than one acquiring company, the acquiring company receiving the
greatest portion of the assets or


<PAGE>
                                      -3-


earning power transferred) which at the time of such transaction would have a
market value of two times the exercise price of the Right.

         If any person becomes an Acquiring Person, each holder of a Right 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. UPON
OCCURRENCE OF ANY OF THE EVENTS DESCRIBED IN THE IMMEDIATELY PRECEDING SENTENCE,
ANY RIGHTS THAT ARE, OR (UNDER CERTAIN CIRCUMSTANCES SPECIFIED IN THE RIGHTS
AGREEMENT) WERE, BENEFICIALLY OWNED BY ANY ACQUIRING PERSON SHALL IMMEDIATELY
BECOME NULL AND VOID.

         At any time after the occurrence of any such event and prior to the
acquisition by such person or group of 50% or more of the outstanding Common
Shares, the Board of Directors may exchange the Rights (other than Rights owned
by such person or group which 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 (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) will be issued
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 earlier of (i) the tenth day after a Shares
Acquisition Date, or (ii) the expiration of the Rights, the Board of Directors
may redeem the Rights in whole, but not in part, at a price of $0.0001 per Right
(the "REDEMPTION PRICE"). The redemption of the Rights may be made effective at
such time on such basis and with such conditions as the Board of Directors in
its sole discretion may establish. 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.

         Other than those provisions relating to the principal economic terms of
the Rights, any of the provisions of the Rights Agreement may be amended by the
Board of Directors of the Company prior to the Distribution Date. After the
Distribution Date, the provisions of the Rights Agreement may be amended by the
Board in order to cure any ambiguity, to make changes that do not adversely
affect the interests of holders of Rights (excluding the interests of any
Acquiring Person), or to shorten or lengthen any time period under the Rights
Agreement; PROVIDED, HOWEVER, that no amendment to adjust the time period
governing redemption shall be made at such time as the Rights are not
redeemable.

         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.

         A copy of the Rights Agreement has been filed with the Securities and
Exchange


<PAGE>
                                      -4-


Commission as an Exhibit to a Current Report on Form 8-K dated          , 1999.
                                                               ---------
A copy of the Rights Agreement is available free of charge from the Company.
This summary description of the Rights does not purport to be complete and is
qualified in its entirety by reference to the Rights Agreement, which is hereby
incorporated herein by reference.

<PAGE>



                                                                    EXHIBIT 99.2
CONTACTS:

  CUBIST PHARMACEUTICALS, INC.                      NOONAN/RUSSO COMMUNICATIONS
  THOMAS A. SHEA                                    CHRISTOPHER MORRISON (MEDIA)
  VICE PRESIDENT & CFO                              (212) 696-4455 X230
  (617) 576-4155                                    [email protected]
  [email protected]



            CUBIST PHARMACEUTICALS, INC. ADOPTS STOCK PURCHASE RIGHTS
                                      PLAN

CAMBRIDGE, MASS., JULY 23, 1999 -- Cubist Pharmaceuticals, Inc. (Nasdaq:CBST)
announced that its Board of Directors declared a special dividend distribution
of a preferred share purchase right for each outstanding share of common stock
of Cubist Pharmaceuticals, Inc. This dividend will be distributed on or about
August 3, 1999 to stockholders of record as of the close of business on that
date.

"The rights plan is designed to gain Board of Director input into any
unsolicited merger or other acquisition attempting to assure that all Cubist
Pharmaceuticals stockholders realize their full value for their Cubist
investment and that all stockholders are treated equitably," said Scott M.
Rocklage, Ph.D., President and CEO of Cubist Pharmaceuticals, Inc. Dr. Rocklage
noted that the company has not received any takeover overture.

The rights will become exercisable only if a person or group (i) acquires 15
percent or more of Cubist Pharmaceutical's common stock, or (ii) announces a
tender offer that would result in ownership of 15 percent or more of the common
stock. Each right would entitle a stockholder to buy one one-hundredth of a
share of preferred stock. Once a person or group has acquired 15 percent or more
of the outstanding common stock of Cubist Pharmaceuticals, each right may
entitle its holder (other than the 15 percent person or group) to purchase
$20.00 worth of newly issued shares of common stock of Cubist Pharmaceuticals at
a price equal to 50 percent of the current market price.

The rights are redeemable at the option of the Board of Directors up until ten
days after public announcement that any person or group has acquired 15 percent
or more of Cubist Pharmaceutical's common stock. The redemption price is $0.0001
per right.

The rights will expire on August 3, 2009, unless redeemed prior to that date.
Distribution of the rights is not taxable to stockholders. A detailed
description of the rights plan will be mailed to Cubist Pharmaceutical's
stockholders at the time of distribution.

Cubist Pharmaceuticals, Inc. is a biopharmaceutical company focused on the
research, development and commercialization of novel antimicrobial drugs to
combat serious and life threatening bacteria and fungi infections. Cubist is
engaged in strategic partnerships with Novartis Pharma AG, Merck & Co., Inc. and
Bristol-Myers Squibb for the discovery and development of novel antiinfective
products, and has formed biotechnology alliances with ArQule, Inc., Helios,
Inc., and Neurogen Corporation.

   For additional information, visit the Company's Internet web site at
           http://www.cubist.com or http://www.noonanrusso.com.

<PAGE>

CUBIST SAFEHARBOR STATEMENT
STATEMENTS CONTAINED HEREIN THAT ARE NOT HISTORICAL FACTS MAY BE FORWARD-LOOKING
STATEMENTS (WITHIN THE MEANING OF SECTION 27A OF THE SECURITIES ACT OF 1933 AND
SECTION 21E OF THE SECURITIES EXCHANGE ACT OF 1934) THAT ARE SUBJECT TO A
VARIETY OF RISKS AND UNCERTAINTIES. THERE ARE A NUMBER OF IMPORTANT FACTORS THAT
COULD CAUSE ACTUAL RESULTS TO DIFFER MATERIALLY FROM THOSE PROJECTED OR
SUGGESTED IN ANY FORWARD-LOOKING STATEMENTS MADE BY THE COMPANY. THESE FACTORS
INCLUDE, BUT ARE NOT LIMITED TO: (I) THE COMPANY'S ABILITY TO SUCCESSFULLY
COMPLETE PRODUCT RESEARCH AND DEVELOPMENT, INCLUDING PRE-CLINICAL AND CLINICAL
STUDIES AND COMMERCIALIZATION; (II) THE COMPANY'S ABILITY TO OBTAIN REQUIRED
GOVERNMENTAL APPROVALS; (III) THE COMPANY'S ABILITY TO ATTRACT AND/OR MAINTAIN
MANUFACTURING, SALES, DISTRIBUTION AND MARKETING PARTNERS; AND (IV) THE
COMPANY'S ABILITY TO DEVELOP AND COMMERCIALIZE ITS PRODUCTS BEFORE ITS
COMPETITORS. ADDITIONAL FACTORS THAT WOULD CAUSE ACTUAL RESULTS TO DIFFER
MATERIALLY FROM THOSE PROJECTED OR SUGGESTED IN ANY FORWARD-LOOKING STATEMENTS
IS CONTAINED IN THE COMPANY'S FILINGS WITH THE SECURITIES AND EXCHANGE
COMMISSION, INCLUDING THOSE FACTORS DISCUSSED UNDER THE CAPTION "RISK FACTORS"
IN THE COMPANY'S ANNUAL REPORT ON FORM 10-K FOR THE FISCAL YEAR ENDED
DECEMBER 31, 1998.


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