<PAGE>

                                                                    Exhibit 4.1

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


                          TRANSKARYOTIC THERAPIES, INC.

                                       AND

                          EQUISERVE TRUST COMPANY, N.A.

                                 AS RIGHTS AGENT




                                RIGHTS AGREEMENT

                             DATED DECEMBER 13, 2000


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



<PAGE>


                                RIGHTS AGREEMENT

RIGHTS AGREEMENT, dated December 13, 2000 (the "Agreement"), between
Transkaryotic Therapies, Inc., a Delaware corporation (the "Company"), and
EquiServe Trust Company, N.A., as Rights Agent (the "Rights Agent").

                               W I T N E S S E T H

WHEREAS, on December 13, 2000 the Board of Directors of the Company (the
"Board") authorized and declared a dividend distribution of one Right for each
share of Common Stock (as hereinafter defined) of the Company outstanding at the
close of business on December 26, 2000 (the "Record Date"), and authorized the
issuance of one Right (as such number may hereinafter be adjusted pursuant to
the provisions of Section 11(i) or Section 11(p) hereof) for each share of
Common Stock of the Company issued between the Record Date (whether originally
issued or delivered from the Company's treasury) and the earlier of the
Distribution Date or the Expiration Date, each Right initially representing the
right to purchase one one-thousandth of a share of Series B Junior Participating
Preferred Stock of the Company having the rights, powers and preferences set
forth in the form of Certificate of Designations attached hereto as EXHIBIT A,
upon the terms and subject to the conditions hereinafter set forth (the
"Rights");

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

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

         (a) "Acquiring Person" shall mean any Person who or which, together
with all Affiliates and Associates of such Person, shall be the Beneficial Owner
of 20% or more of the shares of Common Stock then outstanding, but shall not
include (i) the Company, (ii) any Subsidiary of the Company, (iii) any employee
benefit plan of the Company or of any Subsidiary of the Company, (iv) any Person
organized, appointed or established by the Company for or pursuant to the terms
of any such plan, or (v) an Exempted Person. Notwithstanding the foregoing, (x)
no Person shall become an "Acquiring Person" as the result of an acquisition of
Common Stock by the Company which, by reducing the number of shares outstanding,
increases the proportionate number of shares beneficially owned by such Person
to 20% or more of the shares of Common Stock of the Company then outstanding;
provided, however that if a Person shall become the Beneficial Owner of 20% or
more of the shares of Common Stock of the Company then outstanding as the result
of an acquisition of Common Stock by the Company and shall, following written
notice from, or public disclosure by the Company of such share purchases by the
Company become the Beneficial Owner of any additional Common Stock of the
Company and shall then beneficially own 20% or more of the shares of Common
Stock then outstanding, then such Person shall be deemed to be an "Acquiring
Person" and (y) if the Board 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 (as determined in good faith by the Board of
Directors), but in any event within 15 Business Days, following receipt of
written notice from the Company of such event, of Beneficial Ownership of a
sufficient number of


                                      -1-
<PAGE>


shares of Common Stock so that such Person would no longer be an "Acquiring
Person," as defined pursuant to the foregoing provisions of this paragraph (a),
then such Person shall not be deemed to be an "Acquiring Person" for any
purposes of this Agreement unless and until such Person shall again become an
"Acquiring Person."

         (b) "Act" shall mean the Securities Act of 1933, as amended.

         (c) "Affiliate" and "Associate" shall have the respective meanings
ascribed to such terms in Rule 12b-2 of the General Rules and Regulations under
the Securities Exchange Act of 1934, as amended (the "Exchange Act") as in
effect on the date of this Agreement.

         (d) "Adjustment Shares" shall have the meaning set forth in Section
11(a)(ii).

         (e) A Person shall be deemed the "Beneficial Owner" of, and shall be
deemed to "beneficially own," any securities:

                  (i) which such Person or any of such Person's Affiliates or
         Associates, directly or indirectly, owns or 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 (other than customary agreements with and between
         underwriters and selling group members with respect to a bona fide
         public offering of securities), whether or not in writing, or upon the
         exercise of conversion rights, exchange rights, other rights, warrants
         or options, or otherwise; PROVIDED, HOWEVER, that a Person shall not be
         deemed the "Beneficial Owner" of, or to "beneficially own," (A)
         securities tendered pursuant to a tender or exchange offer made by or
         on behalf of such Person or any of such Person's Affiliates or
         Associates until such tendered securities are accepted for purchase or
         exchange, or (B) securities issuable upon exercise of Rights at any
         time prior to the occurrence of a Triggering Event, or (C) securities
         issuable upon exercise of Rights from and after the occurrence of a
         Triggering Event 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 22 hereof (the "Original
         Rights") or pursuant to Section 11(i) hereof in connection with an
         adjustment made with respect to any Original Rights;

                  (ii) which 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, or any
         comparable or successor rule), including pursuant to any agreement,
         arrangement or understanding (other than customary agreements with and
         between underwriters and selling group members with respect to a bona
         fide public offering of securities), whether or not in writing;
         PROVIDED, HOWEVER, that a Person shall not be deemed the "Beneficial
         Owner" of, or to "beneficially own," any security under this
         subparagraph (ii) as a result of an agreement, arrangement or
         understanding to vote such security if such agreement, arrangement or
         understanding: (A) arises solely from a revocable proxy or consent
         given in response to a public proxy or consent solicitation made


                                      -2-
<PAGE>


         pursuant to, and in accordance with, the applicable provisions of the
         General Rules and Regulations under the Exchange Act, and (B) is not
         then reportable by such Person on Schedule 13D under the Exchange Act
         (or any comparable or successor report); or

                  (iii) which are beneficially owned, directly or indirectly, by
         any other Person (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 (other than customary
         agreements with and between underwriters and selling group members with
         respect to a bona fide public offering of securities) whether or not in
         writing, for the purpose of acquiring, holding, voting (except pursuant
         to a revocable proxy or consent as described in the proviso to
         subparagraph (ii) of this paragraph (e)) or disposing of any voting
         securities of the Company.

For all purposes of this Agreement, any calculation of the number of shares of
Common Stock outstanding at any particular time, including for purposes of
determining the particular percentage of such outstanding shares of Common Stock
of which any Person is the Beneficial Owner, shall be made (i) in accordance
with the last sentence of Rule 13d-3(d)(l)(i) of the General Rules and
Regulations under the Exchange Act and (ii) as if outstanding shares of Series A
Convertible Preferred Stock had been converted into shares of Common Stock at
the then applicable conversion rate specified in the Company's Certificate of
Incorporation, as amended.

         (f) "Board" shall have the meaning set forth in the WHEREAS clause at
the beginning of this Agreement.

         (g) "Business Day" shall mean any day other than a Saturday, Sunday or
a day on which banking institutions in the Commonwealth of Massachusetts are
authorized or obligated by law or executive order to close.

         (h) "Close of business" on any given date shall mean 5:00 p.m., Boston
time, on such date; PROVIDED, HOWEVER, that if such date is not a Business Day
it shall mean 5:00 p.m., Boston time, on the next succeeding Business Day.

         (i) "Common Stock" shall mean the common stock, $0.01 par value, of the
Company, except that "Common Stock" when used with reference to any Person other
than the Company shall mean the capital stock of such Person with the greatest
voting power, or the equity securities or other equity interest having power to
control or direct the management, of such Person.

         (j) "Common stock equivalents" shall have the meaning set forth in
Section 11(a)(iii) hereof.

         (k) "Company" shall have the meaning set forth in the introductory
paragraph hereof.

         (l) "Current market price" shall have the meaning set forth in Section
11(d)(i) hereof.


                                      -3-
<PAGE>


         (m) "Current Value" shall have the meaning set forth in Section
11(a)(iii) hereof.

         (n) "Distribution Date" shall have the meaning set forth in Section
3(a) hereof.

         (o) "Equivalent Preferred Stock" shall have the meaning set forth in
Section 11(b) hereof.

         (p) "Exchange Act" shall have the meaning set forth in Section 1(c)
hereof.

         (q) "Exchange Ratio" shall have the meaning set forth in Section 24(a)
hereof.

         (r) "Exempted Person" shall mean Warburg, Pincus Equity Partner, L.P.,
a Delaware limited partnership, Warburg, Pincus & Co., a New York general
partnership, E.M. Warburg, Pincus & Co., LLC, a New York limited liability
company, Warburg, Pincus Netherlands Equity Partners I, C.V., Warburg, Pincus
Netherlands Equity Partners II, C.V., Warburg, Pincus Netherlands Equity
Partners III, C.V. (together, "Warburg Pincus"), which as of the date hereof,
beneficially own an aggregate of 10,000 shares of the Company's Series A
Convertible Preferred Stock, or approximately 3,571,429 shares of Common Stock
(on an as converted basis), representing approximately 13.6% of the Common Stock
outstanding as of the date hereof, unless and until such time as Warburg Pincus,
together with their Affiliates and Associates, directly or indirectly, becomes
the Beneficial Owner of more than 30% of the Common Stock then outstanding
(other than under circumstances described in the second sentence of Section 1(a)
hereof (replacing for this purpose all references in Section 1(a) to 20% with
30%)), in which event, Warburg Pincus immediately shall cease to be an Exempted
Person.

         (s) "Expiration Date" shall have the meaning set forth in Section 7(a)
hereof.

         (t) "Final Expiration Date" shall mean the close of business on
December 13, 2010.

         (u) "Person" shall mean any individual, firm, corporation, partnership,
trust, association, limited liability company or other entity.

         (v) "Preferred Stock" shall mean shares of Series B Junior
Participating Preferred Stock, $0.01 par value, of the Company having the rights
and preferences set forth in the form of Certificate of Designations attached to
this Agreement as EXHIBIT A and, to the extent that there is not a sufficient
number of shares of Series B Junior Participating Preferred Stock authorized to
permit the full exercise of the Rights, any other series of Preferred Stock,
$0.01 par value, of the Company designated for such purpose containing terms
substantially similar to the terms of the Series B Junior Participating
Preferred Stock.

         (w) "Principal Party" shall have the meaning set forth in Section 13(b)
hereof.

         (x) "Purchase Price" shall have the meaning set forth in Section 4(a)
hereof.

         (y) "Record Date" shall have the meaning set forth in the WHEREAS
clause at the beginning of this Agreement.


                                      -4-
<PAGE>


         (z) "Redemption Date" shall have the meaning set forth in Section 7(a)
hereof.

         (aa) "Redemption Price" shall have the meaning set forth in Section
23(a) hereof.

         (bb) "Rights" shall have the meaning set forth in the WHEREAS clause at
the beginning of this Agreement.

         (cc) "Rights Agent" shall have the meaning set forth in the
introductory paragraph hereof.

         (dd) "Rights Certificates" shall have the meaning set forth in Section
3(a) hereof.

         (ee) "Section 11(a)(ii) Event" shall mean an acquisition of Common
Stock described in the first sentence of Section 11(a)(ii) hereof.

         (ff) "Section 11(a)(ii) Trigger Date" shall have the meaning set forth
in Section 11(a)(iii) hereof.

         (gg) "Section 13 Event" shall mean any event described in clauses (x),
(y) or (z) of Section 13(a) hereof.

         (hh) "Series A Convertible Preferred Stock" shall mean shares of Series
A Convertible Preferred Stock, $0.01 par value, of the Company issued and
outstanding on the date hereof.

         (ii) "Spread" shall have the meaning set forth in Section 11(a)(iii)
hereof.

         (jj) "Stock Acquisition Date" shall mean the first date of public
announcement (which, for purposes of this definition, shall include, 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;
PROVIDED, HOWEVER that, if such Person is deemed not to be an "Acquiring Person"
pursuant to clause (y) of Section 1(a) hereof, no Stock Acquisition Date shall
be deemed to have occurred.

         (kk) "Subsidiary" shall mean, with reference to any Person, any
corporation of which an amount of voting securities sufficient to elect at least
a majority of the directors of such corporation is beneficially owned, directly
or indirectly, by such Person, or otherwise controlled by such Person.

         (ll) "Substitution Period" shall have the meaning set forth in Section
11(a)(iii) hereof.

         (mm) "Trading Day" shall have the meaning set forth in Section 11(d)(i)
hereof.

         (nn) "Triggering Event" shall mean any Section 11(a)(ii) Event or any
Section 13 Event.


                                      -5-
<PAGE>


     Section 2. APPOINTMENT OF RIGHTS AGENT. The Company hereby appoints the
Rights Agent to act as agent for the Company and the holders of the Rights (who,
in accordance with Section 3 hereof, shall prior to the Distribution Date also
be the holders of the Common Stock) 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.

     Section 3. ISSUANCE OF RIGHTS.

         (a) Until the earlier of (i) the close of business on the tenth
Business Day (or such later date as may be determined by the Board) after the
Stock Acquisition Date (or, if the tenth Business Day after the Stock
Acquisition Date occurs before the Record Date, the close of business on the
Record Date), or (ii) the close of business on the tenth Business Day (or such
later date as may be determined by action of the Board) after the date that a
tender or exchange offer 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 Person organized, appointed or established by the Company
for or pursuant to the terms of any such plan, or any Exempted Person) is first
published or sent or given within the meaning of Rule 14d-2 of the General Rules
and Regulations under the Exchange Act, if upon consummation thereof, such
Person would be the Beneficial Owner of 20% or more of the shares of Common
Stock then outstanding, (the earlier of (i) and (ii) being herein referred to as
the "Distribution Date"), (x) the Rights will be evidenced by the certificates
for the Common Stock registered in the names of the holders of the Common Stock
(which certificates for Common Stock shall be deemed also to be certificates for
Rights) and not by separate certificates, and (y) the Rights will be
transferable only in connection with the transfer of the underlying shares of
Common Stock (including a transfer to the Company). As soon as practicable after
the Distribution Date, the Rights Agent will send by first-class, insured,
postage prepaid mail, to each record holder of the Common Stock as of the close
of business on the Distribution Date, at the address of such holder shown on the
records of the Company, one or more rights certificates, in substantially the
form of EXHIBIT B hereto (the "Rights Certificates"), evidencing one Right for
each share of Common Stock so held, subject to adjustment as provided herein. In
addition, in connection with the issuance or sale of shares of Common Stock
following the Distribution Date and prior to the redemption or expiration of the
Rights, the Company (i) shall, with respect to shares of Common Stock so issued
or sold pursuant to the exercise of stock options or under any employee plan or
arrangement, or upon the exercise, conversion or exchange of securities issued
by the Company prior to the Distribution Date including, without limitation,
shares of Series A Convertible Preferred Stock and (ii) may, in any other case,
if deemed necessary or appropriate by the Board, issue Rights Certificates
representing the appropriate number of Rights in connection with such issuance
or sale; provided, however, that (x) no such Rights Certificate shall be issued
if, and to the extent that, the Company shall be advised by counsel that such
issuance would create a significant risk of material adverse tax consequences to
the Company or the Person to whom such Rights Certificate would be issued, and
(y) no such Rights Certificate shall be issued if, and to the extent that,
appropriate adjustment shall otherwise have been made in lieu of the issuance
thereof. In the event that an adjustment in the number of Rights per share of
Common Stock has been made pursuant to Sections 11(i) or 11(p) hereof, at the
time of distribution of the Right


                                      -6-
<PAGE>


Certificates, the Company shall make the necessary and appropriate rounding
adjustments (in accordance with Section 14(a) hereof) so that Rights
Certificates representing only whole numbers of Rights are distributed and cash
is paid in lieu of any fractional Rights. As of and after the Distribution Date,
the Rights will be evidenced solely by such Rights Certificates.

         (b) As promptly as practicable following the Record Date, the Company
will send a copy of a Summary of Rights to Purchase Preferred Stock, in
substantially the form attached hereto as EXHIBIT C, by first-class, postage
prepaid mail, to each record holder of the Common Stock as of the close of
business on the Record Date, at the address of such holder shown on the records
of the Company. With respect to certificates for the Common Stock outstanding as
of the close of business on the Record Date, until the Distribution Date, the
Rights will be evidenced by such certificates for the Common Stock and the
registered holders of the Common Stock shall also be the registered holders of
the associated Rights.

         (c) Rights shall be issued (i) in respect of all shares of Common Stock
that are issued (either as an original issuance or from the Company's treasury)
after the Record Date but prior to the earlier of the Distribution Date or the
Expiration Date and (ii) in connection with the issuance or sale of Common Stock
following the Distribution Date and prior to the Expiration Date upon the
exercise of stock options or under any employee benefit plan or arrangement, or
upon the exercise, conversion or exchange of securities, granted or issued by
the Company prior to the Distribution Date, including, without limitation,
shares of Series A Convertible Preferred Stock. Certificates representing such
shares of Common Stock (including, without limitation, certificates issued upon
transfer or exchange of Common Stock) shall also be deemed to be certificates
for Rights, and shall bear the following legend:

         This certificate also evidences and entitles the holder hereof to
         certain Rights as set forth in the Rights Agreement between
         Transkaryotic Therapies, Inc. ( the "Company") and EquiServe Trust
         Company (the "Rights Agent") dated as of December 13, 2000, as the same
         may be amended, restated or renewed from time to time (the "Rights
         Agreement"), the terms of which are hereby incorporated herein by
         reference and a copy of which is on file at the principal offices of
         the Company. Under certain circumstances, as set forth in the Rights
         Agreement, such Rights will be evidenced by separate certificates and
         will no longer be evidenced by this certificate. The Company will mail
         to the holder of this certificate a copy of the Rights Agreement, as in
         effect on the date of mailing, without charge promptly after receipt of
         a written request therefor. Under certain circumstances set forth in
         the Rights Agreement, Rights issued to, or held by, any Person who is,
         was or becomes an Acquiring Person or any Affiliate or Associates
         thereof (as such terms are defined in the Rights Agreement), whether
         currently held by or on behalf of such Person or by any subsequent
         holder, may become null and void.

With respect to such certificates containing the foregoing legend, until the
earlier of (i) the Distribution Date or (ii) the Expiration Date, the Rights
associated with the Common Stock


                                      -7-
<PAGE>


represented by such certificates shall be evidenced by such certificates alone
and registered holders of Common Stock shall also be the registered holders of
the associated Rights. Notwithstanding this Section 3(c), the omission of a
legend shall not affect the enforceability of any part of this Rights Agreement
or the rights of any holder of the Rights.

         (d) Until the earlier of the Distribution Date or the Expiration Date,
the transfer of any certificates representing shares of Common Stock in respect
of which Rights have been issued shall also constitute the transfer of the
Rights associated with such shares of Common Stock. In the event that the
Company purchases or acquires any shares of Common Stock after the Record Date
but prior to the Distribution Date, any Rights associated with such shares of
Common Stock shall be deemed cancelled and retired so that the Company shall not
be entitled to exercise any Rights associated with the shares of Common Stock
which are no longer outstanding.

     Section 4. FORM OF RIGHTS CERTIFICATES.

         (a) The Rights Certificates (and the forms of election to purchase,
certification and assignment to be printed on the reverse thereof) shall each be
substantially in the form set forth in EXHIBIT B hereto and may have such marks
of identification or designation and such legends, summaries or endorsements
printed thereon as the Company may deem appropriate and as are not inconsistent
with the provisions of this Agreement, or as may be required to comply with any
applicable law or with any rule or regulation made pursuant thereto or with any
rule or regulation of any stock exchange or over-the-counter market on which the
Rights may from time to time be listed, or to conform to usage. Subject to the
provisions of Sections 7, 11 and 22 hereof, the Rights Certificates, whenever
distributed, shall entitle the holders thereof to purchase such number of one
one-thousandths of a share of Preferred Stock as shall be set forth therein at
the price set forth therein (such exercise price per one one-thousandth of a
share, the "Purchase Price"), but the amount and type of securities purchasable
upon the exercise of each Right and the Purchase Price thereof shall be subject
to adjustment as provided herein.

(b) Any Rights Certificate issued pursuant to Section 3, Section 11(i) or
Section 22 hereof that represents Rights beneficially owned by persons known to
be: (i) an Acquiring Person or an Associate or Affiliate of an Acquiring Person,
(ii) a transferee of an Acquiring Person (or of any such Associate or Affiliate)
who becomes a transferee after the Acquiring Person becomes such, or (iii) a
transferee of an Acquiring Person (or of any such Associate or Affiliate) who
becomes a transferee prior to or concurrently with the Acquiring Person becoming
such and receives such Rights pursuant to either (A) a transfer (whether or not
for consideration) from the Acquiring Person to holders of equity interests in
such Acquiring Person or to any Person with whom such Acquiring Person has any
continuing agreement, arrangement or understanding (whether or not in writing)
regarding the transferred Rights or (B) a transfer which the Board has
determined is part of a plan, arrangement or understanding (whether or not in
writing) that has as a primary purpose or effect avoidance of Section 7(e)
hereof, and any Rights Certificate issued pursuant to Section 6 or Section 11
hereof upon transfer, exchange, replacement or adjustment of any other Rights
Certificate referred to in this sentence, shall contain (to the extent feasible)
the following legend:


                                      -8-
<PAGE>


         The Rights represented by this Rights Certificate are or were
         beneficially owned by a Person who was or became an Acquiring Person or
         an Affiliate or Associate of an Acquiring Person (as such terms are
         defined in the Rights Agreement). Accordingly, this Rights Certificate
         and the Rights represented hereby may become null and void in the
         circumstances specified in Section 7(e) of such Agreement.

The provisions of Section 7(e) hereof shall be operative whether or not the
foregoing legend is contained on any such Rights Certificate.

     Section 5. COUNTERSIGNATURE AND REGISTRATION.

         (a) The Rights Certificates shall be executed on behalf of the Company
by its President and Chief Executive Officer or any Vice President, either
manually or by facsimile signature, and shall have affixed thereto the Company's
seal or a facsimile thereof, which shall be attested by the Secretary of the
Company, either manually or by facsimile signature. The Rights Certificates
shall be manually countersigned by the Rights Agent and shall not be valid for
any purpose unless so countersigned. In case any officer of the Company who
shall have signed any of the Rights Certificates shall cease to be such officer
of the Company before countersignature by the Rights Agent and issuance and
delivery by the Company, such Rights Certificates, nevertheless, may be
countersigned by the Rights Agent and issued and delivered by the Company with
the same force and effect as though the person who signed such Rights
Certificates had not ceased to be such officer of the Company; and any Rights
Certificates may be signed on behalf of the Company by any person who, at the
actual date of the execution of such Rights Certificate, shall 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.

         (b) Following the Distribution Date, the Rights Agent shall keep or
cause to be kept, at its office designated as the appropriate place for
surrender of Rights Certificates upon exercise or transfer, books for
registration and transfer of the Rights Certificates issued hereunder. Such
books shall show 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, the Certificate number and the date of each of the Rights
Certificates.

     Section 6. TRANSFER, SPLIT UP, COMBINATION AND EXCHANGE OF RIGHTS
CERTIFICATES; MUTILATED, DESTROYED, LOST OR STOLEN RIGHTS CERTIFICATES.

         (a) Subject to the provisions of Section 4(b), Section 7(e) and Section
14 hereof, at any time after the close of business on the Distribution Date, and
at or prior to the close of business on the Expiration Date, any Rights
Certificate or Certificates (other than Rights Certificates representing Rights
that have become void pursuant to Section 7(e) hereof or that have been
exchanged pursuant to Section 24 hereof) may be transferred, split up, combined
or exchanged for another Rights Certificate or Certificates, entitling the
registered holder to purchase a like number of one one-thousandths of a share of
Preferred Stock (or, following a Triggering Event, Common Stock, other
securities, cash or other assets, as the case may be) as


                                      -9-
<PAGE>


the Rights Certificate or Certificates surrendered then entitled such holder (or
former holder in the case of a transfer) to purchase. Any registered holder
desiring to transfer, split up, combine or exchange any Rights Certificate or
Certificates shall make such request in writing delivered to the Rights Agent,
and shall surrender the Rights Certificate or Certificates to be transferred,
split up, combined or exchanged, with the form of assignment and certificate
appropriately executed, 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 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 shall, subject to Section 4(b), Section 7(e) and Section 14 hereof,
countersign and deliver to the Person entitled thereto a Rights Certificate or
Rights Certificates, as the case may be, as so requested. The Company may
require payment of a sum sufficient to cover any tax or governmental charge that
may be imposed in connection with any transfer, split up, combination or
exchange of Rights Certificates.

         (b) 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
or security reasonably satisfactory to them, and 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 countersignature and delivery to the registered
owner 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 including, without limitation, the restrictions on
exercisability set forth in Section 9(c), Section 11(a)(iii) and Section 23
hereof) 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 and
the certificate 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 aggregate Purchase Price with respect to the total number of one
one-thousandths of a share of Preferred Stock (or other shares, securities, cash
or other assets, as the case may be) as to which such surrendered Rights are
then exercisable, at or prior to the earliest of (i) the Final Expiration Date,
(ii) the time at which the Rights are redeemed as provided in Section 23 hereof
(the "Redemption Date") or (iii) the time at which such Rights are exchanged as
provided in Section 24 hereof (the earliest of (i), (ii) and (iii) being herein
referred to as the "Expiration Date").

         (b) The Purchase Price for each one one-thousandth of a share of
Preferred Stock pursuant to the exercise of a Right shall initially be $289 and
shall be subject to adjustment from time to time as provided in Sections 11 and
13(a) hereof and shall be payable in lawful money of the United States of
America in accordance with paragraph (c) below.


                                      -10-
<PAGE>


         (c) Upon receipt of a Rights Certificate representing exercisable
Rights, with the form of election to purchase and the certificate duly executed,
accompanied by payment, with respect to each Right so exercised, of the Purchase
Price per one one-thousandth of a share of Preferred Stock (or other shares,
securities, cash or other assets, as the case may be) to be purchased and an
amount equal to any applicable transfer tax, the Rights Agent shall, subject to
Section 20(k) hereof, thereupon promptly (i) (A) requisition from any transfer
agent of the shares of Preferred Stock (or make available, if the Rights Agent
is the transfer agent for such shares) certificates for the total number of one
one-thousandths of a share of Preferred Stock to be purchased and the Company
hereby authorizes its transfer agent to comply with such requests, or (B) if the
Company shall have elected to deposit the total number of shares of Preferred
Stock issuable upon exercise of the Rights hereunder with a depositary agent,
requisition from the depositary agent depositary receipts representing such
number of one one-thousandths of a share of Preferred Stock as are to be
purchased (in which case certificates for the shares of Preferred Stock
represented by such receipts shall be deposited by the transfer agent with the
depositary agent) and the Company hereby directs the depositary agent to comply
with such requests, (ii) requisition from the Company the amount of cash, if
any, to be paid in lieu of fractional shares in accordance with Section 14
hereof, (iii) after receipt of such certificates or depositary receipts, cause
the same to be delivered to or upon the order of the registered holder of such
Rights Certificate, registered in such name or names as may be designated by
such holder, and (iv) after receipt thereof, deliver such cash, if any, to or
upon the order of the registered holder of such Rights Certificate. The payment
of the Purchase Price (as such amount may be reduced pursuant to Section
11(a)(iii) hereof) may be made in cash or by certified bank check or money order
payable to the order of the Company. In the event that the Company is obligated
to issue other securities (including Common Stock) of the Company, pay cash
and/or distribute other property pursuant to Section 11(a) hereof, the Company
shall make all arrangements necessary so that such other securities, cash and/or
other property are available for distribution by the Rights Agent, if and when
appropriate.

         (d) In case the registered holder of any Rights Certificate shall
exercise less than all the Rights evidenced thereby, a new Rights Certificate
evidencing Rights equivalent to the Rights remaining unexercised shall be issued
by the Rights Agent and 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, subject to the provisions of Section 14 hereof.

         (e) Notwithstanding anything in this Agreement to the contrary, from
and after the first occurrence of a Section 11(a)(ii) Event, any Rights
beneficially owned by (i) an Acquiring Person or an Associate or Affiliate of an
Acquiring Person, (ii) a transferee of an Acquiring Person (or of any such
Associate or Affiliate) who becomes a transferee after the Acquiring Person
becomes such, or (iii) a transferee of an Acquiring Person (or of any such
Associate or Affiliate) who becomes a transferee prior to or concurrently with
the Acquiring Person becoming such and receives such Rights pursuant to either
(A) a transfer (whether or not for consideration) from the Acquiring Person to
holders of equity interests in such Acquiring Person or to any Person with whom
the Acquiring Person has any continuing agreement, arrangement or understanding
(whether or not in writing) regarding the transferred Rights or (B) a transfer
which the Board has determined is part of a plan, arrangement or understanding
(whether or not in writing) that has as a primary purpose or effect avoidance of
this Section 7(e), shall become null and void without any further action and no
holder of such Rights shall have


                                      -11-
<PAGE>


any rights whatsoever with respect to such Rights, whether under any provision
of this Agreement or otherwise. The Company shall use all reasonable efforts to
insure that the provisions of this Section 7(e) and Section 4(b) hereof are
complied with, but shall have no liability to any holder of Rights Certificates
or other Person as a result of its failure to make any determinations with
respect to an Acquiring Person or its Affiliates, Associates or transferees
hereunder. No 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 the
preceding sentence or any Associate or Affiliate thereof or to any nominee of
such Acquiring Person, Associate or Affiliate; and any Right Certificate
delivered to the Rights Agent for transfer to an Acquiring Person whose Rights
would be void pursuant to the preceding sentence shall be cancelled.

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

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

     Section 9. RESERVATION AND AVAILABILITY OF CAPITAL STOCK.

         (a) The Company covenants and agrees that it will cause to be reserved
and kept available out of its authorized and unissued shares of Preferred Stock
(and, following the occurrence of a Section 11(a)(ii) Event, out of its
authorized and unissued shares of Common Stock and/or other securities or out of
its authorized and issued shares held in its treasury), the number of shares of
Preferred Stock (and, following the occurrence of a Section 11(a)(ii) Event,
Common Stock and/or other securities) that, as provided in this Agreement
including Section 11(a)(iii) hereof, will be sufficient to permit the exercise
in full of all outstanding Rights.

         (b) So long as the shares of Preferred Stock (and, following the
occurrence of a Section 11(a)(ii) Event, Common Stock and/or other securities)
issuable and deliverable upon the exercise of the Rights may be listed on any
national securities exchange or automated quotation system, the Company shall
use its best efforts to cause, from and after such time as the Rights


                                      -12-
<PAGE>


become exercisable, all shares reserved for such issuance to be so listed upon
official notice of issuance upon such exercise.

         (c) The Company shall use its best efforts to (i) file, as soon as
practicable following the earliest date after the first occurrence of a Section
11(a)(ii) Event on which the consideration to be delivered by the Company upon
exercise of the Rights has been determined in accordance with Section 11(a)(iii)
hereof, or as soon as is required by law following the Distribution Date, as the
case may be, a registration statement under the Act, with respect to the
securities purchasable upon exercise of the Rights on an appropriate form, (ii)
cause such registration statement to become effective as soon as practicable
after such filing, and (iii) cause such registration statement to remain
effective (with a prospectus at all times meeting the requirements of the Act)
until the earlier of (A) the date as of which the Rights are no longer
exercisable for such securities, and (B) the Expiration Date. The Company will
also take such action as may be appropriate under, or to ensure compliance with,
the securities or "blue sky" laws of the various states in connection with the
exercisability of the Rights. The Company may temporarily suspend, for a period
of time not to exceed ninety (90) days after the date set forth in clause (i) of
the first sentence of this Section 9(c), the exercisability of the Rights in
order to prepare and file such registration statement and permit it to become
effective. Upon any such suspension, the Company shall issue a public
announcement stating that the exercisability of the Rights has been temporarily
suspended, as well as a public announcement at such time as the suspension is no
longer in effect. Notwithstanding any provision of this Agreement to the
contrary, the Rights shall not be exercisable in any jurisdiction unless the
requisite registration or qualification in such jurisdiction shall have been
effected or obtained.

         (d) The Company covenants and agrees that it will take all such action
as may be necessary to ensure that all one one-thousandths of a share of
Preferred Stock (and, following the occurrence of a Section 11(a)(ii) Event,
Common Stock and/or other securities) delivered upon exercise of Rights shall,
at the time of delivery of the certificates for such shares (subject to payment
of the Purchase Price), be duly and validly authorized and issued and fully paid
and nonassessable.

         (e) The Company further covenants and agrees that it will pay when due
and payable any and all federal and state transfer taxes and charges that may be
payable in respect of the issuance or delivery of the Rights Certificates and of
any certificates for a number of one one-thousandths of a share of Preferred
Stock (or Common Stock and/or other securities, as the case may be) upon the
exercise of Rights. The Company shall not, however, be required (i) to pay any
transfer tax that may be payable in respect of any transfer or delivery of
Rights Certificates to a Person other than, or the issuance or delivery of a
number of one one-thousandths of a share of Preferred Stock (or Common Stock
and/or other securities, as the case may be) in respect of a name other than
that of, the registered holder of the Rights Certificate evidencing Rights
surrendered for exercise or (ii) to issue or deliver any certificates for a
number of one one-thousandths of a share of Preferred Stock (or Common Stock
and/or other securities, as the case may be) in a name other than that of the
registered holder upon the exercise of any Rights until such tax shall have 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
satisfaction that no such tax is due.


                                      -13-
<PAGE>


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

     Section 11. ADJUSTMENT OF PURCHASE PRICE, NUMBER 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) In the event the Company shall at any time after the date of
this Agreement (A) declare a dividend on the Preferred Stock payable in shares
of Preferred Stock, (B) subdivide the outstanding Preferred Stock, (C) combine
the outstanding Preferred Stock into a smaller number of shares, or (D) issue
any shares of its capital stock in a reclassification of the Preferred Stock
(including any such reclassification in connection with a consolidation or
merger in which the Company is the continuing or surviving corporation), except
as otherwise provided in this Section 11(a) and Section 7(e) hereof, the
Purchase Price in effect at the time of the record date for such dividend or of
the effective date of such subdivision, combination or reclassification, and the
number and kind of shares of Preferred Stock or capital stock, as the case may
be, issuable on such date, shall be proportionately adjusted so that the holder
of any Right exercised after such time shall be entitled to receive, upon
payment of the Purchase Price then in effect, the aggregate number and kind of
shares of Preferred Stock or capital stock, as the case may be, which, if such
Right had been exercised immediately prior to such date and at a time when the
Preferred Stock transfer books of the Company were open, he would have owned
upon such exercise and been entitled to receive by virtue of such dividend,
subdivision, combination or reclassification. If an event occurs that would
require an adjustment under both this Section 11(a)(i) and Section 11(a)(ii)
hereof, the adjustment provided for in this Section 11(a)(i) shall be in
addition to, and shall be made prior to, any adjustment required pursuant to
Section 11(a)(ii) hereof.

         (ii) Subject to Section 24 of this Agreement, in the event that any
Person, alone or together with its Affiliates or Associates, becomes an
Acquiring Person, then, promptly


                                      -14-
<PAGE>


following the first occurrence of such event, proper provision shall be made so
that each holder of a Right (except as provided below and in Section 7(e)
hereof) shall thereafter have the right to receive (subject to the last sentence
of Section 23(a)), upon exercise thereof at the then current Purchase Price in
accordance with the terms of this Agreement, in lieu of a number of one
one-thousandths of a share of Preferred Stock, such number of shares of Common
Stock of the Company that equals the result obtained by (x) multiplying the then
current Purchase Price by the then number of one one-thousandths of a share of
Preferred Stock 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, shall thereafter be referred to as the
"Purchase Price" for each Right and for all purposes of this Agreement) by 50%
of the current market price (determined pursuant to Section 11(d) hereof) per
share of Common Stock on the date of such first occurrence (such number of
shares, the "Adjustment Shares").

         (iii) In the event that the number of shares of Common Stock that are
authorized by the Company's Certificate of Incorporation 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 in accordance with
the foregoing subparagraph (ii) of this Section 11(a), the Company shall: (A)
determine the excess of (1) the value of the Adjustment Shares issuable upon the
exercise of a Right (the "Current Value") over (2) the Purchase Price (such
excess, the "Spread"), and (B) with respect to each Right, make adequate
provision to substitute for the Adjustment Shares, upon payment of the
applicable Purchase Price, (1) cash, (2) a reduction in the Purchase Price, (3)
Common Stock or other equity securities of the Company (including, without
limitation, shares, or units of shares, of preferred stock which the Board has
deemed to have the same value as shares of Common Stock (such shares of
preferred stock, "common stock equivalents")), (4) debt securities of the
Company, (5) other assets, or (6) any combination of the foregoing, having an
aggregate value equal to the Current Value, where such aggregate value has been
determined by the Board based upon the advice of a nationally recognized
investment banking firm selected by the Board; PROVIDED, HOWEVER, if the Company
shall not have made adequate provision to deliver value pursuant to clause (B)
above within thirty (30) days following the later of (x) the first occurrence of
a Section 11(a)(ii) Event and (y) the date on which the Company's right of
redemption pursuant to Section 23(a) expires (the later of (x) and (y) being
referred to herein as the "Section 11(a)(ii) Trigger Date"), then the Company
shall be obligated to deliver, upon the surrender for exercise of a Right and
without requiring payment of the Purchase Price, shares of Common Stock (to the
extent available) and then, if necessary, cash, which shares and/or cash have an
aggregate value equal to the Spread. If the Board shall determine in good faith
that it is likely that sufficient additional shares of Common Stock could be
authorized for issuance upon exercise in full of the Rights, the thirty (30) day
period set forth above may be extended to the extent necessary, but not more
than ninety (90) days after the Section 11(a)(ii) Trigger Date, in order that
the Company may seek shareholder approval for the authorization of such
additional shares (such period, as it may be extended, the "Substitution
Period"). To the extent that the Company determines that some action need be
taken pursuant to the first and/or second sentences of this Section 11(a)(iii),
the Company (x) shall provide, subject to Section 7(e) hereof, that such action
shall apply uniformly to all outstanding Rights, and (y) may suspend the
exercisability of the Rights until the expiration of the Substitution Period in
order to seek any authorization of additional shares and/or to decide the
appropriate form of distribution to be made pursuant to such first sentence and
to determine the value thereof. In the event of any such suspension, the Company
shall issue a public


                                      -15-
<PAGE>


announcement stating that the exercisability of the Rights has been temporarily
suspended, as well as a public announcement at such time as the suspension is no
longer in effect. For purposes of this Section 11(a)(iii), the value of the
Common Stock shall be the current market price (as determined pursuant to
Section 11(d) hereof) per share of the Common Stock on the Section 11(a)(ii)
Trigger Date and the value of any "common stock equivalent" shall be deemed to
have the same value as the Common Stock on such date.

         (b) In case the Company shall fix a record date for the issuance of
rights, options or warrants to all holders of Preferred Stock entitling them to
subscribe for or purchase (for a period expiring within forty-five (45) calendar
days after such record date) Preferred Stock (or shares having the same rights,
privileges and preferences as the shares of Preferred Stock ("equivalent
preferred stock")) or securities convertible into Preferred Stock or equivalent
preferred stock at a price per share of Preferred Stock or per share of
equivalent preferred stock (or having a conversion price per share, if a
security convertible into Preferred Stock or equivalent preferred stock) less
than the current market price (as determined pursuant to Section 11(d) hereof)
per share of Preferred Stock on such record date, the Purchase Price to be in
effect after such record date shall be determined by multiplying the Purchase
Price in effect immediately prior to such record date by a fraction, the
numerator of which shall be the number of shares of Preferred Stock outstanding
on such record date, plus the number of shares of Preferred Stock which the
aggregate offering price of the total number of shares of Preferred Stock and/or
equivalent preferred stock so to be offered (and/or the aggregate initial
conversion price of the convertible securities so to be offered) would purchase
at such current market price, and the denominator of which shall be the number
of shares of Preferred Stock outstanding on such record date, plus the number of
additional shares of Preferred Stock and/or equivalent preferred stock to be
offered for subscription or purchase (or into which the convertible securities
so to be offered are initially convertible). In case such subscription price may
be paid by delivery of consideration part or all of which may be in a form other
than cash, the value of such consideration shall be as determined in good faith
by the Board, whose determination shall be described in a statement filed with
the Rights Agent and shall be conclusive for all purposes. Shares of Preferred
Stock owned by or held for the account of the Company shall not be deemed
outstanding for the purpose of any such computation. Such adjustment shall be
made successively whenever such a record date is fixed, and in the event that
such rights, options or warrants are not so issued, the Purchase Price shall be
adjusted to be the Purchase Price which would then be in effect if such record
date had not been fixed.

         (c) In case the Company shall fix a record date for a distribution to
all holders of Preferred Stock (including any such distribution made in
connection with a consolidation or merger in which the Company is the continuing
corporation) of evidences of indebtedness, cash (other than a regular quarterly
cash dividend out of the earnings or retained earnings of the Company), assets
(other than a dividend payable in Preferred Stock, but including any dividend
payable in stock other than Preferred Stock) or subscription rights or warrants
(excluding those referred to in Section 11(b) hereof), the Purchase Price to be
in effect after such record date shall be determined by multiplying the Purchase
Price in effect immediately prior to such record date by a fraction, the
numerator of which shall be the current market price (as determined pursuant to
Section 11(d) hereof) per share of Preferred Stock on such record date, less the
fair market value (as determined in good faith by the Board, whose determination
shall be described in a statement filed with the Rights Agent and shall be
conclusive for all purposes) of the portion of the cash,


                                      -16-
<PAGE>


assets or evidences of indebtedness so to be distributed or of such subscription
rights or warrants applicable to a share of Preferred Stock and the denominator
of which shall be such current market price (as determined pursuant to Section
11(d) hereof) per share of Preferred Stock on such record date. Such adjustments
shall be made successively whenever such a record date is fixed, and in the
event that such distribution is not so made, the Purchase Price shall be
adjusted to be the Purchase Price which would have been in effect if such record
date had not been fixed.

         (d) (i) For the purpose of any computation hereunder, other than
computations made pursuant to Section 11(a)(iii) hereof, the "current market
price" per share of Common Stock on any date shall be deemed to be the average
of the daily closing prices per share of such Common Stock for the thirty (30)
consecutive Trading Days (as such term is hereinafter defined) immediately prior
to such date, and for purposes of computations made pursuant to Section
11(a)(iii) hereof, the "current market price" per share of Common Stock on any
date shall be deemed to be the average of the daily closing prices per share of
such Common Stock for the ten (10) consecutive Trading Days immediately
following such date; PROVIDED, HOWEVER, that in the event that the current
market price per share of the Common Stock is determined during a period
following the announcement by the issuer of such Common Stock of (A) a dividend
or distribution on such Common Stock payable in shares of such Common Stock or
securities convertible into shares of such Common Stock (other than the Rights),
or (B) any subdivision, combination or reclassification of such Common Stock,
and prior to the expiration of the requisite thirty (30) Trading Day or ten (10)
Trading Day period, as set forth above, after the ex-dividend date for such
dividend or distribution, or the record date for such subdivision, combination
or reclassification occurs, then, and in each such case, the "current market
price" shall be properly adjusted to take into account ex-dividend or post
record date trading. The closing price for each day shall be the last sale
price, regular way, or, in case no such sale takes place on such day, the
average of the closing bid and asked prices, regular way, in either case as
reported in the principal consolidated transaction reporting system with respect
to securities listed or admitted to trading on the principal national securities
exchange on which the shares of Common Stock are listed or admitted to trading
or, if the shares of Common Stock 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 the low asked prices in the over-the-counter market,
as reported by The Nasdaq Stock Market, Inc. ("Nasdaq") or such other system
then in use, or, if on any such date the shares of Common Stock 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 Common Stock
selected by the Board. If on any such date no market maker is making a market in
the Common Stock, the fair value of such shares on such date as determined in
good faith by the Board shall be used. The term "Trading Day" shall mean a day
on which Nasdaq or any national securities exchange on which the shares of
Common Stock are listed or admitted to trading is open for the transaction of
business or, if the shares of Common Stock are not listed or admitted to trading
on Nasdaq or any national securities exchange, a Business Day. If the Common
Stock is not publicly held or not so listed or traded, "current market price"
per share shall mean the fair value per share as determined in good faith by the
Board, whose determination shall be described in a statement filed with the
Rights Agent and shall be conclusive for all purposes.

         (ii) For the purpose of any computation hereunder, the "current market
price" per share of Preferred Stock shall be determined in the same manner as
set forth above for the


                                      -17-
<PAGE>


Common Stock in clause (i) of this Section 11(d) (other than the last sentence
thereof). If the current market price per share of Preferred Stock cannot be
determined in the manner provided above or if the Preferred Stock is not
publicly held or listed or traded in a manner described in clause (i) of this
Section 11(d), the "current market price" per share of Preferred Stock shall be
conclusively deemed to be an amount equal to 1,000 (as such number may be
appropriately adjusted for such events as stock splits, stock dividends and
recapitalizations with respect to the Common Stock occurring after the date of
this Agreement) multiplied by the current market price per share of the Common
Stock. If neither the Common Stock nor the Preferred Stock is publicly held or
so listed or traded, "current market price" per share of the Preferred Stock
shall mean the fair value per share as determined in good faith by the Board,
whose determination shall be described in a statement filed with the Rights
Agent and shall be conclusive for all purposes. For all purposes of this
Agreement, the "current market price" of one one-thousandth of a share of
Preferred Stock shall be equal to the "current market price" of one share of
Preferred Stock divided by 1000.

         (e) Anything herein to the contrary notwithstanding, no adjustment in
the Purchase Price shall be required unless such adjustment would require an
increase or decrease of at least one percent (1%) in the Purchase Price;
PROVIDED, HOWEVER, that any adjustments which by reason of this Section 11(e)
are not required to be made shall be carried forward and taken into account in
any subsequent adjustment. All calculations under this Section 11 shall be made
to the nearest cent or to the nearest ten-millionth of a share of Preferred
Stock, or hundred-thousandth of a share of Common Stock or other security, as
the case may be. Notwithstanding the first sentence of this Section 11(e), any
adjustment required by this Section 11 shall be made no later than the earlier
of (i) three years from the date of the transaction which mandates such
adjustment, or (ii) the Expiration Date.

         (f) If as a result of an adjustment made pursuant to Section 11(a)(ii)
or Section 13(a) hereof, the holder of any Right thereafter exercised shall
become entitled to receive any securities other than Preferred Stock, thereafter
the number of such other securities so receivable upon exercise of any Right and
the Purchase Price thereof shall be subject to adjustment from time to time in a
manner and on terms as nearly equivalent as practicable to the provisions with
respect to the Preferred Stock contained in Sections 11(a), (b), (c), (e), (g),
(h), (i), (j), (k) and (m), and the provisions of Sections 7, 9, 10, 13 and 14
hereof with respect to the Preferred Stock shall apply on like terms to any such
other securities; PROVIDED, HOWEVER, that the Company shall not be liable for
its inability to reserve and keep available for issuance upon exercise of the
Rights pursuant to Section 11(a)(ii) a number of shares of Common Stock greater
than the number then authorized by the Company's Certificate of Incorporation
but not outstanding or reserved for other purposes.

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

         (h) Unless the Company shall have exercised its election as provided in
Section 11(i), upon each adjustment of the Purchase Price as a result of the
calculations made in


                                      -18-
<PAGE>


Sections 11(b) and (c), each Right outstanding immediately prior to the making
of such adjustment shall thereafter evidence the right to purchase, at the
adjusted Purchase Price, that number of one one-thousandths of a share of
Preferred Stock (calculated to the nearest ten-millionth) obtained by (i)
multiplying (x) the number of one one-thousandths of a share covered by a Right
immediately prior to this adjustment, by (y) the Purchase Price in effect
immediately prior to such adjustment of the Purchase Price, and (ii) dividing
the product so obtained by the Purchase Price in effect immediately after such
adjustment of the Purchase Price.

         (i) The Company may elect on or after the date of any adjustment of the
Purchase Price to adjust the number of Rights, in lieu of any adjustment in the
number of one one-thousandths of a share of Preferred Stock purchasable upon the
exercise of a Right. Each of the Rights outstanding after the adjustment in the
number of Rights shall be exercisable for the number of one one-thousandths of a
share of Preferred Stock for which a Right was exercisable immediately prior to
such adjustment. Each Right held of record prior to such adjustment of the
number of Rights shall become that number of Rights (calculated to the nearest
one-hundred- thousandth) obtained by dividing the Purchase Price in effect
immediately prior to adjustment of the Purchase Price by the Purchase Price in
effect immediately after adjustment of the Purchase Price. The Company shall
make a public announcement of its election to adjust the number of Rights,
indicating the record date for the adjustment, and, if known at the time, the
amount of the adjustment to be made. This record date may be the date on which
the Purchase Price is adjusted or any day thereafter, but, if the Rights
Certificates have been issued, shall be at least ten (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 shall, as promptly as practicable, cause to be distributed to holders of
record of Rights Certificates on such record date Rights Certificates
evidencing, subject to Section 14 hereof, the additional Rights to which such
holders shall be entitled as a result of such adjustment, or, at the option of
the Company, shall cause to be distributed to such holders of record in
substitution and replacement for the 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
shall be entitled after such adjustment. Rights Certificates so to be
distributed shall 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 shall 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-thousandths of a share of Preferred Stock issuable upon
the exercise of the Rights, the Rights Certificates theretofore and thereafter
issued may continue to express the Purchase Price per one one-thousandth of a
share and the number of one one-thousandths of a share which were expressed in
the initial Rights Certificates issued hereunder.

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


                                      -19-
<PAGE>


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

         (m) Anything in this Section 11 to the contrary notwithstanding, the
Company shall be entitled to make such reductions in the Purchase Price, in
addition to those adjustments expressly required by this Section 11, as and to
the extent that in their good faith judgment the Board shall determine to be
advisable in order that any (i) consolidation or subdivision of the Preferred
Stock, (ii) issuance wholly for cash of any shares of Preferred Stock at less
than the current market price, (iii) issuance wholly for cash of shares of
Preferred Stock or securities which by their terms are convertible into or
exchangeable for shares of Preferred Stock, (iv) stock dividends or (v) issuance
of rights, options or warrants referred to in this Section 11, hereafter made by
the Company to holders of its Preferred Stock shall not be taxable to such
stockholders.

         (n) The Company covenants and agrees that it shall not, at any time
after the Distribution Date, (i) consolidate with any other Person (other than a
Subsidiary of the Company in a transaction that complies with Section 11(o)
hereof), (ii) merge with or into any other Person (other than a Subsidiary of
the Company in a transaction which complies with Section 11(o) hereof), or (iii)
sell or transfer (or permit any Subsidiary to sell or transfer), in one
transaction, or a series of related 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 or Persons (other than the
Company and/or any of its Subsidiaries in one or more transactions each of which
complies with Section 11(o) hereof), if (x) at the time of or immediately after
such consolidation, merger or sale there are any charter or bylaw provisions or
any rights, warrants or other instruments or securities outstanding or
agreements in effect that would substantially diminish or otherwise eliminate
the benefits intended to be afforded by the Rights or (y) prior to,
simultaneously with or immediately after such consolidation, merger or sale, the
shareholders of the Person who constitutes, or would constitute, the "Principal
Party" for purposes of Section 13(a) hereof shall have received a distribution
of Rights previously owned by such Person or any of its Affiliates and
Associates. The Company shall not consummate any consolidation, merger, sale or
transfer described in clause (i), (ii) or (iii) of the prior sentence unless
prior thereto the Company and such other Person shall have executed and
delivered to the Rights Agent a supplemental agreement evidencing compliance
with this Section 11(n).

         (o) The Company covenants and agrees that, after the Distribution Date,
it will not, except as permitted by Section 23, Section 24 or Section 27 hereof,
take (or permit any Subsidiary to take) any action if at the time such action is
taken it is reasonably foreseeable that


                                      -20-
<PAGE>


such action will diminish substantially or otherwise eliminate the benefits
intended to be afforded by the Rights.

         (p) Anything in this Agreement to the contrary notwithstanding, in the
event that the Company shall at any time after the Record Date and prior to the
Distribution Date (i) declare or pay any dividend on the outstanding shares of
Common Stock payable in shares of Common Stock, (ii) subdivide the outstanding
shares of Common Stock, or (iii) combine the outstanding shares of Common Stock
into a smaller number of shares, the number of Rights associated with each share
of Common Stock then outstanding, or issued or delivered thereafter but prior to
the Distribution Date, shall be proportionately adjusted so that the number of
Rights thereafter associated with each share of Common Stock following any such
event shall equal the result obtained by multiplying the number of Rights
associated with each share of Common Stock immediately prior to such event by a
fraction, the numerator of which shall be the number of shares of Common Stock
outstanding immediately prior to the occurrence of such event and the
denominator of which shall be the number of shares of Common Stock outstanding
immediately following the occurrence of such event.

     Section 12. CERTIFICATE OF ADJUSTED PURCHASE PRICE OR NUMBER OF SHARES.
Whenever an adjustment is made as provided in Section 11 or Section 13 hereof,
the Company shall promptly (a) prepare a certificate setting forth such
adjustment and a brief statement of the facts accounting for such adjustment,
(b) file with the Rights Agent, and with each transfer agent for the Preferred
Stock and the Common Stock, 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 shares of Common
Stock) in accordance with Section 26 hereof. The Rights Agent shall be fully
protected in relying on any such certificate and on any adjustment therein
contained and shall not be deemed to have knowledge of any adjustment unless and
until it shall have received such certificate.

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

         (a) In the event that, at any time after a Person has become an
Acquiring Person, (x) the Company shall consolidate with, or merge with and
into, any other Person (other than a Subsidiary of the Company in a transaction
that complies with Section 11(o) hereof), and the Company shall not be 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 11(o) hereof) shall consolidate with, or merge with or into, the
Company, and the Company shall be the continuing or surviving corporation of
such consolidation or merger and, in connection with such consolidation or
merger, all or part of the outstanding shares of Common Stock shall be changed
into or exchanged for stock or other securities of any other Person or cash or
any other property, or (z) the Company shall sell or otherwise transfer (or one
or more of its Subsidiaries shall sell or otherwise transfer), in one
transaction or a series of related 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 Person or Persons (other than the Company
or any Subsidiary of the Company in one or more transactions each of which
complies with Section 11(o) hereof), then, and in each such case, proper
provision shall be made so that: (i) each holder of a Right, except as provided
in Section 7(e) hereof, shall thereafter have the right to receive, upon the
exercise thereof at the then current Purchase Price in accordance with


                                      -21-
<PAGE>


the terms of this Agreement, such number of validly authorized and issued, fully
paid, non-assessable and freely tradeable shares of Common Stock of the
Principal Party (as such term is hereinafter defined), not subject to any liens,
encumbrances, rights of first refusal or other adverse claims, as shall be equal
to the result obtained by (1) multiplying the then current Purchase Price by the
number of one one-thousandths of a share of Preferred Stock 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 one one-thousandths of a share
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, shall be referred to as the "Purchase
Price" for each Right and for all purposes of this Agreement) by 50% of the
current market price (determined pursuant to Section 11(d)(i) hereof) per share
of the Common Stock of such Principal Party on the date of consummation of such
Section 13 Event; (ii) such Principal Party shall thereafter be liable for, and
shall assume, by virtue of such Section 13 Event, all the obligations and duties
of the Company pursuant to this Agreement; (iii) the term "Company" shall
thereafter be deemed to refer to such Principal Party, it being specifically
intended that, subject to clause (v) below, the provisions of Section 11 hereof
shall apply only to such Principal Party following the first occurrence of a
Section 13 Event; (iv) such Principal Party shall take such steps (including,
but not limited to, the reservation of a sufficient number of shares of its
Common Stock) in connection with the consummation of any such transaction as may
be necessary to assure that the provisions hereof shall thereafter be
applicable, as nearly as reasonably may be, in relation to its shares of Common
Stock thereafter deliverable upon the exercise of the Rights; and (v) the
provisions of Section 11(a)(ii) hereof shall be of no effect following the first
occurrence of any Section 13 Event.

         (b) "Principal Party" shall mean

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

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

PROVIDED, HOWEVER, that in any such case, (1) if the Common Stock of such Person
is not at such time and has not been continuously over the preceding twelve (12)
month period registered under Section 12 of the Exchange Act, and such Person is
a direct or indirect Subsidiary of another Person the Common Stock of which is
and has been so registered, "Principal Party" shall refer to such other Person;
(2) in case such Person is a Subsidiary, directly or indirectly, of more than
one Person, the Common Stocks of two or more of which are and have been so
registered, "Principal Party" shall refer to whichever of such Persons is the
issuer of the Common Stock having the greatest aggregate market value; and (3)
in case such Person is owned, directly or


                                      -22-
<PAGE>


indirectly, by a joint venture formed by two or more Persons that are not owned,
directly or indirectly, by the same Person, the rules set forth in (1) and (2)
above shall apply to each of the chains of ownership having an interest in such
joint venture as if such party were a "Subsidiary" of both or all of such joint
ventures and the Principal Parties in each such chain shall bear the obligations
set forth in this Section 13 in the same ratio as their direct or indirect
interests in such Person bear to the total of such interests.

         (c) The Company shall not consummate any such consolidation, merger,
sale or transfer unless the Principal Party shall have a sufficient number of
authorized shares of its Common Stock which 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 such Principal Party shall
have executed and delivered to the Rights Agent a supplemental agreement
providing for the terms set forth in paragraphs (a) and (b) of this Section 13
and further providing that, as soon as practicable after the date of any
consolidation, merger or sale of assets mentioned in paragraph (a) of this
Section 13, the Principal Party will

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

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

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

The provisions of this Section 13 shall similarly apply to successive mergers or
consolidations or sales or other transfers. In the event that a Section 13 Event
shall occur at the same time as, or at any time after, the occurrence of a
Section 11(a)(ii) Event, the Rights which have not theretofore been exercised
shall thereafter become exercisable in the manner described in Section 13(a).

     Section 14. FRACTIONAL RIGHTS AND FRACTIONAL SHARES.

         (a) The Company shall not be required to issue fractions of Rights,
except prior to the Distribution Date as provided in Section 11(i) or (p)
hereof, or to distribute Rights Certificates that evidence fractional Rights. In
lieu of such fractional Rights, there shall 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 purposes of this Section 14(a), the
current market value of a whole Right shall be the closing price of the Rights
for the Trading Day immediately prior to the date on which such fractional
Rights would have been otherwise issuable. The closing price of the Rights for
any day shall be the last sale price, regular way, or, in case no such sale
takes place on


                                      -23-
<PAGE>


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 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 the 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. 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 shall be used.

         (b) The Company shall not be required to issue fractions of shares of
Preferred Stock (other than fractions which are integral multiples of one
one-thousandth of a share of Preferred Stock) upon exercise of the Rights or to
distribute certificates that evidence fractional shares of Preferred Stock
(other than fractions which are integral multiples of one one-thousandth of a
share of Preferred Stock). Fractional shares of Preferred Stock in integral
multiples of one one-thousandth of a share of Preferred Stock may, at the
election of the Company, be evidenced by depositary receipts; provided, however,
that holders of such depositary receipts shall have all of the designations and
the powers, preferences and rights, and the qualifications, limitations and
restrictions to which they are entitled as beneficial owners of the shares of
Preferred Stock represented by such depositary receipts. In lieu of fractional
shares of Preferred Stock (other than fractions which are integral multiples of
one one-thousandth of a share of Preferred Stock), the Company shall 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 one-thousandth of a share of Preferred Stock. For purposes
of this Section 14(b), the current market value of one one-thousandth of a share
of Preferred Stock shall be one one-thousandth of the closing price of a share
of Preferred Stock (as determined pursuant to Section 11(d)(ii) hereof) for the
Trading Day immediately prior to the date of such exercise.

         (c) Following the occurrence of a Triggering Event, the Company shall
not be required to issue fractions of shares of Common Stock upon exercise of
the Rights or to distribute certificates which evidence fractional shares of
Common Stock. In lieu of fractional shares of Common Stock, the Company shall
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 price of one (1) share of Common Stock (as determined pursuant to
Section 11(d)(i) hereof) for the Trading Day immediately prior to the date of
such exercise.

         (d) The holder of a Right by the acceptance of the Rights expressly
waives his right to receive any fractional Rights or any fractional shares upon
exercise of a Right, except as permitted by this Section 14.

     Section 15. RIGHTS OF ACTION. All rights of action in respect of this
Agreement, except the rights of action expressly given to the Rights Agent in
Section 18 hereof, are vested in the respective registered holders of the Rights
Certificates (and, prior to the Distribution Date, the registered holders of the
Common Stock); and any registered holder of any Rights Certificate (or,


                                      -24-
<PAGE>


prior to the Distribution Date, of the Common Stock), 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 Stock), 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 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 shall be entitled to specific performance
of the obligations hereunder and injunctive relief against actual or threatened
violations of the obligations hereunder of any Person subject to this Agreement.

     Section 16. 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 Common Stock;

         (b) after the Distribution Date, the Rights Certificates are
transferable only on the registry books of the Rights Agent if surrendered at
the office of the Rights Agent designated for such purposes, duly endorsed or
accompanied by a proper instrument of transfer and with the appropriate forms
and certificates duly completed and fully executed;

         (c) subject to Section 6(a) and Section 7(f) hereof, the Company and
the Rights Agent may deem and treat the person in whose name a Rights
Certificate (or, prior to the Distribution Date, the associated Common Stock
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 Stock certificate made by anyone
other than the Company or the Rights Agent) for all purposes whatsoever, and
neither the Company nor the Rights Agent, subject to the last sentence of
Section 7(e) hereof, shall be required to 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 shall have any liability to any holder of 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 prevent the issuance of any such order, decree or ruling and to have
any such order, decree or ruling lifted or otherwise overturned as soon as
possible.

     Section 17. RIGHTS CERTIFICATE HOLDER NOT DEEMED A STOCKHOLDER. No holder,
as such, of any Rights Certificate shall be entitled to vote, receive dividends
or be deemed for any purpose the holder of the number of one one-thousandths of
a share of Preferred Stock or any other securities of the Company which may at
any time be issuable on the exercise of the Rights


                                      -25-
<PAGE>


represented thereby, nor shall 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 (except as
provided in Section 25 hereof), or to receive dividends or subscription rights,
or otherwise, until the Right or Rights evidenced by such Rights Certificate
shall have been exercised in accordance with the provisions hereof.

     Section 18. CONCERNING THE RIGHTS AGENT.

         (a) 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
disbursements 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 in the premises.

         (b) The Rights Agent shall be protected and shall incur no liability
for or in respect of any action taken, suffered or omitted by it in connection
with its administration of this Agreement in reliance upon any Rights
Certificate or certificate for Common Stock or for other securities of the
Company, instrument of assignment or transfer, power of attorney, endorsement,
affidavit, letter, notice, direction, consent, certificate, statement, or other
paper or document believed by it to be genuine and to be signed, executed and,
where necessary, verified or acknowledged, by the proper Person or Persons, or
otherwise upon the advice of counsel as set forth in Section 20 hereof.

     Section 19. MERGER OR CONSOLIDATION OR CHANGE OF NAME OF RIGHTS AGENT.

         (a) Any corporation into which the Rights Agent or any successor Rights
Agent may be merged or with which it may be consolidated, or any corporation
resulting from any merger or consolidation to which the Rights Agent or any
successor Rights Agent shall be a party, or any corporation succeeding to the
corporate trust or stock transfer business of the Rights Agent or any successor
Rights Agent, shall be the successor to the Rights Agent under this Agreement
without the execution or filing of any paper or any further act on the part of
any of the parties hereto; PROVIDED, HOWEVER, that such corporation would be
eligible for appointment as a successor Rights Agent under the provisions of
Section 21 hereof. In case at the time such successor Rights Agent shall succeed
to the agency created by this Agreement, any of the Rights Certificates shall
have been countersigned but not delivered, any such successor Rights Agent may
adopt the countersignature of a predecessor Rights Agent and deliver such Rights
Certificates so countersigned; and in case at that time any of the Rights
Certificates shall not have been countersigned, any successor Rights Agent may
countersign such Rights Certificates either in the name of the predecessor or in
the name of the successor Rights Agent; and in all


                                      -26-
<PAGE>


such cases such Rights Certificates shall have the full force provided in the
Rights Certificates and in this Agreement.

         (b) In case at any time the name of the Rights Agent shall be changed
and at such time any of the Rights Certificates shall 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 shall not have 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 shall
have the full force provided in the Rights Certificates and in this Agreement.

     Section 20. DUTIES OF RIGHTS AGENT. The Rights Agent undertakes the duties
and obligations imposed by this Agreement upon the following terms and
conditions, by all of which the Company and the holders of Rights Certificates,
by their acceptance thereof, shall 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 shall be full and
complete authorization and protection to the Rights Agent as to any action taken
or omitted by it in good faith and in accordance with such opinion.

         (b) Whenever in the performance of its duties under this Agreement the
Rights Agent shall deem it necessary or desirable that any fact or matter
(including, without limitation, the identity of any Acquiring Person and the
determination of "current market price") be proved or established by the Company
prior to taking or suffering any action hereunder, such fact or matter (unless
other evidence in respect thereof be herein specifically prescribed) may be
deemed to be conclusively proved and established by a certificate signed by the
President and Chief Executive Officer, any Vice President, the Treasurer, any
Assistant Treasurer, or the Secretary of the Company and delivered to the Rights
Agent; and such certificate shall be full authorization to the Rights Agent for
any action taken or suffered in good faith by it under the provisions of this
Agreement in reliance upon such certificate.

         (c) The Rights Agent shall be liable hereunder only for its own gross
negligence, bad faith or willful misconduct.

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

         (e) The Rights Agent shall not be under any responsibility in respect
of the validity of this Agreement or the execution and delivery hereof (except
the due execution hereof by the Rights Agent) or in respect of the validity or
execution of any Rights Certificate (except its countersignature thereof); nor
shall it be responsible for any breach by the Company of any covenant or
condition contained in this Agreement or in any Rights Certificate; nor shall it
be responsible for any adjustment required under the provisions of Section 11,
Section 13 or Section 24 hereof or responsible for the manner, method or amount
of any such adjustment or the ascertaining of the existence of facts that would
require any such adjustment (except with respect


                                      -27-
<PAGE>


to the exercise of Rights evidenced by Rights Certificates after receipt of a
certificate describing any such adjustment, delivered pursuant to Section 12);
nor shall it by any act hereunder be deemed to make any representation or
warranty as to the authorization or reservation of any shares of Common Stock or
Preferred Stock to be issued pursuant to this Agreement or any Rights
Certificate or as to whether any shares of Common Stock or Preferred Stock will,
when so issued, be validly authorized and issued, fully paid and nonassessable.

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

         (g) The Rights Agent is hereby authorized and directed to accept
instructions with respect to the performance of its duties hereunder from the
President and Chief Executive Officer, any Vice President, the Secretary, the
Treasurer or any Assistant Treasurer of the Company, and to apply to such
officers for advice or instructions in connection with its duties, and it shall
not be liable for any action taken or suffered to be taken by it in good faith
in accordance with instructions of any such officer. Any application by the
Rights Agent for written instructions from the Company may, at the option of the
Rights Agent, set forth in writing any action proposed to be taken or omitted by
the Rights Agent with respect to its duties or obligations under this Rights
Agreement and the date on and/or after which such action shall be taken or
omitted and the Rights Agent shall not be liable for any action taken or omitted
in accordance with a proposal included in any such application on or after the
date specified therein (which date shall not be less than five Business Days
after the date any such officer actually receives such application, unless any
such officer shall have consented in writing to an earlier date) unless, prior
to taking or omitting any such action, the Rights Agent has received written
instructions in response to such application specifying the action to be taken
or omitted.

         (h) The Rights Agent and any stockholder, director, officer or employee
of the Rights Agent may buy, sell or deal in any of the Rights or other
securities of the Company or become pecuniarily interested in any transaction in
which the Company may be interested, or contract with or lend money to the
Company or otherwise act as fully and freely as though it were not Rights Agent
under this Agreement. Nothing herein shall preclude the Rights Agent from acting
in any other capacity for the Company or for any other legal entity.

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

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


                                      -28-
<PAGE>


         (k) If, with respect to any Rights Certificate surrendered to the
Rights Agent for exercise or transfer, the certificate attached to the form of
assignment or form of election to purchase, as the case may be, has not been
completed, the Company and the Rights Agent will deem the beneficial owner of
the rights evidenced by such Rights Certificate to be an Acquiring Person or an
Affiliate or Associate thereof and such assignment or election to purchase will
not be honored.

     Section 21. CHANGE OF RIGHTS AGENT. The Rights Agent or any successor
Rights Agent may resign and be discharged from its duties under this Agreement
upon thirty (30) days' notice in writing mailed to the Company, and to each
transfer agent of the Common Stock and Preferred Stock, by registered or
certified mail, and to the holders of the Rights Certificates by first-class
mail. The Company may remove the Rights Agent or any successor Rights Agent upon
thirty (30) days' notice in writing, mailed to the Rights Agent or successor
Rights Agent, as the case may be, and to each transfer agent of the Common Stock
and Preferred Stock, by registered or certified mail, and to the holders of the
Rights Certificates by first-class mail. If the Rights Agent shall resign or be
removed or shall otherwise become incapable of acting, the Company shall appoint
a successor to the Rights Agent. If the Company shall fail to make such
appointment within a period of thirty (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 shall, with such notice, submit his Rights Certificate
for inspection by the Company), then any 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 such a court, shall be (a) a corporation organized and doing
business under the laws of the United States (or of any state of the United
States) in good standing, which is authorized under such laws to exercise
corporate trust or stock transfer powers and is subject to supervision or
examination by federal or state authority and which has at the time of its
appointment as Rights Agent a combined capital and surplus of at least
$50,000,000 or (b) an affiliate of a corporation described in clause (a) of this
sentence. After appointment, the successor Rights Agent shall be vested with the
same powers, rights, duties and responsibilities as if it had been originally
named as Rights Agent without further act or deed; but the predecessor Rights
Agent shall deliver and transfer to the successor Rights Agent any property at
the time held by it hereunder, and execute and deliver any further assurance,
conveyance, act or deed necessary for the purpose. Not later than the effective
date of any such appointment, the Company shall file notice thereof in writing
with the predecessor Rights Agent and each transfer agent of the Common Stock
and the Preferred Stock, 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 21, however, or any defect therein, shall not affect the legality
or validity of the resignation or removal of the Rights Agent or the appointment
of the successor Rights Agent, as the case may be.

     Section 22. ISSUANCE OF NEW RIGHTS CERTIFICATES. Notwithstanding any of the
provisions of this Agreement or of the Rights to the contrary, the Company may,
at its option, issue new Rights Certificates evidencing Rights in such form as
may be approved by the Board 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.


                                      -29-
<PAGE>


     Section 23. REDEMPTION.

         (a) The Board may, at its option, at any time prior to the earlier of
(i) the close of business on the tenth Business Day (or such later date as may
be determined by the Board pursuant to clause (i) of the first sentence of
Section 3(a) with respect to the Distribution Date) following the Stock
Acquisition Date (or, if the Stock Acquisition Date shall have occurred prior to
the Record Date, the close of business on the tenth Business Day following the
Record Date) or (ii) the Final Expiration Date, redeem all but not less than all
the then outstanding Rights at a redemption price of $0.001 per Right, as such
amount may be appropriately adjusted to reflect any stock split, stock dividend
or similar transaction occurring after the date hereof (such redemption price
being hereinafter referred to as the "Redemption Price"). The redemption of the
Rights by the Board may be made effective at such time, on such basis and with
such conditions as the Board in its sole discretion may establish. The Company
may, at its option, pay the Redemption Price in cash, shares of Common Stock
(based on the "current market price," as defined in Section 11(d)(i) hereof, of
the Common Stock at the time of redemption) or any other form of consideration,
or any combination of any of the foregoing, deemed appropriate by the Board.
Notwithstanding anything contained in this Agreement to the contrary, the Rights
shall not be exercisable after the first occurrence of a Section 11(a)(ii) Event
until such time as the Company's right of redemption hereunder has expired.

         (b) Immediately upon the action of the Board ordering the redemption of
the Rights, evidence of which shall have been filed with the Rights Agent and
without any further action and without any notice, the right to exercise the
Rights shall terminate and the only right thereafter of the holders of Rights
shall be to receive the Redemption Price for each Right so held. Promptly after
the action of the Board ordering the redemption of the Rights, the Company shall
give notice of such redemption to the Rights Agent and the holders of the then
outstanding Rights by mailing such notice to all such holders at each holder's
last address as it appears 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 Stock. Any notice which is mailed in the manner herein provided shall be
deemed given, whether or not the holder receives the notice. Each such notice of
redemption will state the method by which the payment of the Redemption Price
will be made.

         (c) In the event of a redemption of the Rights in accordance with this
Agreement, the Company may, at its option, discharge all of its obligations with
respect to the Rights by (i) issuing a press release announcing the manner of
redemption of the Rights in accordance with this Agreement and (ii) mailing
payment of the Redemption Price to the registered holders of the Rights at their
last addresses as they appear on the registry books of the Rights Agent or,
prior to the Distribution Date, on the registry books of the Transfer Agent of
the Common Shares, and upon such action, all outstanding Rights and Right
Certificates shall be null and void without any further action by the Company.

     Section 24. EXCHANGE.

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


                                      -30-
<PAGE>


include, without limitation, any Rights issued after the Distribution Date) for
shares of Common Stock at an exchange ratio of one share of Common Stock per
Right, appropriately adjusted to reflect any stock split, stock dividend or
similar transaction occurring after the date hereof (such exchange ratio being
hereinafter referred to as the "Exchange Ratio"). Notwithstanding the foregoing,
the Board shall not be empowered to effect such exchange at any time after any
Person (other than the Company, any Subsidiary of the Company, any employee
benefit plan of the Company or any such Subsidiary, or any entity holding Common
Stock for or pursuant to the terms of any such plan), together with all
Affiliates and Associates of such Person, becomes the Beneficial Owner of 50% or
more of the shares of Common Stock then outstanding.

         (b) Immediately upon the action of the Board ordering the exchange of
any Rights pursuant to subsection (a) of this Section 24, evidence of which
shall have been filed with the Rights Agent, and without any further action and
without any notice, the right to exercise such Rights shall terminate and the
only right thereafter of a holder of such Rights shall be to receive that number
of shares of Common Stock equal to the number of such Rights held by such holder
multiplied by the Exchange Ratio. The Company shall promptly give public notice
of any such exchange; PROVIDED, HOWEVER, that the failure to give, or any defect
in, such notice shall not affect the validity of such exchange. The Company
promptly shall mail a notice of any such exchange to all of the holders of such
Rights at their last addresses as they appear upon the registry books of the
Rights Agent. Any notice which is mailed in the manner herein provided shall be
deemed given, whether or not the holder receives the notice. Each such notice of
exchange shall state the method by which the exchange of shares of Common Stock
for Rights will be effected and, in the event of any partial exchange, the
number of Rights which will be exchanged. Any partial exchange shall be effected
pro rata based on the number of Rights (other than Rights which have become void
pursuant to the provisions of Section 7(e) hereof) held by each holder of
Rights.

         (c) In any exchange pursuant to this Section 24, the Company, at its
option, may substitute Preferred Stock (or equivalent preferred stock, as such
term is defined in Section 11(b) hereof) for shares of Common Stock exchangeable
for Rights, at the initial rate of one one-thousandth of a share of Preferred
Stock (or equivalent preferred stock) for each share of Common Stock, as
appropriately adjusted to reflect adjustments in the voting rights of the
Preferred Stock pursuant to Section 3(A) of the Certificate of Designations
attached hereto as EXHIBIT A, so that the fraction of a share of Preferred Stock
(or equivalent preferred stock) delivered in lieu of each share of Common Stock
shall have the same voting rights as one share of Common Stock.

         (d) In the event that there shall not be sufficient shares of Common
Stock or Preferred Stock issued but not outstanding or authorized but unissued
to permit any exchange of Rights as contemplated in accordance with this Section
24, the Company shall take all such action as may be necessary to authorize
additional shares of Common Stock or Preferred Stock for issuance upon exchange
of the Rights.

         (e) The Company shall not be required to issue fractions of shares of
Common Stock or to distribute certificates which evidence fractional shares of
Common Stock. In lieu of such fractional shares of Common Stock, there shall be
paid to the registered holders of the Right Certificates with regard to which
such fractional shares of Common Stock would otherwise be


                                      -31-
<PAGE>


issuable, an amount in cash equal to the same fraction of the current market
value of a whole share of Common Stock. For the purposes of this subsection (e),
the current market value of a whole share of Common Stock shall be the closing
price per share of Common Stock (as determined pursuant to the second sentence
of Section 11(d)(i) hereof) for the Trading Day immediately prior to the date of
exchange pursuant to this Section 24.

     Section 25. NOTICE OF CERTAIN EVENTS.

         (a) In case the Company shall propose, at any time after the
Distribution Date, (i) to pay any dividend payable in stock of any class to the
holders of Preferred Stock or to make any other distribution to the holders of
Preferred Stock (other than a regular quarterly cash dividend out of earnings or
retained earnings of the Company), or (ii) to offer to the holders of Preferred
Stock rights or warrants to subscribe for or to purchase any additional shares
of Preferred Stock or shares of stock of any class or any other securities,
rights or options, or (iii) to effect any reclassification of its Preferred
Stock (other than a reclassification involving only the subdivision of
outstanding shares of Preferred Stock), or (iv) to effect any consolidation or
merger into or with any other Person (other than a Subsidiary of the Company in
a transaction which complies with Section 11(o) hereof), 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 transaction or a series of related transactions,
of more than 50% of the assets or earning power of the Company and its
Subsidiaries (taken as a whole) to any other Person or Persons (other than the
Company and/or any of its Subsidiaries in one or more transactions each of which
complies with Section 11(o) hereof), or (v) to effect the liquidation,
dissolution or winding up of the Company, then, in each such case, the Company
shall give to each holder of a Rights Certificate, to the extent feasible and in
accordance with Section 26 hereof, a notice of such proposed action, which shall
specify the record date for the purposes of such stock dividend, 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 shares of Preferred
Stock, if any such date is to be fixed, and such notice shall be so given in the
case of any action covered by clause (i) or (ii) above at least twenty (20) days
prior to the record date for determining holders of the shares of Preferred
Stock for purposes of such action, and in the case of any such other action, at
least twenty (20) days prior to the date of the taking of such proposed action
or the date of participation therein by the holders of the shares of Preferred
Stock, whichever shall be the earlier.

         (b) In case a Section 11(a)(ii) Event shall occur, then, in any such
case, (i) the Company shall as soon as practicable thereafter give to each
holder of a Rights Certificate, to the extent feasible and in accordance with
Section 26 hereof, a notice of the occurrence of such event, which shall specify
the event and the consequences of the event to holders of Rights under Section
11(a)(ii) hereof, and (ii) all references in the preceding paragraph to
Preferred Stock shall be deemed thereafter to refer also to Common Stock and/or,
if appropriate, other securities.

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


                                      -32-
<PAGE>


                 Transkaryotic Therapies, Inc.
                 195 Albany  Street
                 Cambridge, MA 02139
                 Attention: Vice President, Finance and Chief Financial Officer

                 with a copy to:
                 Hale and Dorr LLP
                 60 State Street
                 Boston, MA 02109
                 Attention: David E. Redlick, Esq.


Subject to the provisions of Section 21, 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 shall be sufficiently given or made if
sent by first-class mail, postage prepaid, addressed (until another address is
filed in writing with the Company) as follows:

                 EquiServe Trust Company, N.A.
                 150 Royall Street
                 Canton, MA  02021
                 Attention: 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, if
prior to the Distribution Date, to the holder of certificates representing
shares of Common Stock) shall be sufficiently given or made if sent by
first-class mail, postage prepaid, addressed to such holder at the address of
such holder as shown on the registry books of the Company.

     Section 27. SUPPLEMENTS AND AMENDMENTS. Except as provided in the
penultimate sentence of this Section 27, for so long as the Rights are then
redeemable, the Company may, in its sole and absolute discretion, and the Rights
Agent shall, if the Company so directs, supplement or amend any provision of
this Agreement in any respect without the approval of any holders of the Rights.
At any time when the Rights are no longer redeemable, except as provided in the
penultimate sentence of this Section 27, the Company may, by approval of at
least 75% of the members of the Board, and the Rights Agent shall, if the
Company so directs, supplement or amend this Agreement without the approval of
any holders of Rights in order (i) to cure any ambiguity or (ii) to correct or
supplement any provision contained herein which may be defective or inconsistent
with any other provisions herein, PROVIDED that no such supplement or amendment
shall adversely affect the interests of the holders of Rights as such (other
than an Acquiring Person or an Affiliate or Associate of an Acquiring Person).
Upon the delivery of a certificate from an appropriate officer of the Company
which states that the proposed supplement or amendment is in compliance with the
terms of this Section 27, the Rights Agent shall execute such supplement or
amendment. Notwithstanding anything contained in this Agreement to the contrary,
no supplement or amendment shall be made which changes the Redemption Price.
Prior to the Distribution Date, the interests of the holders of Rights shall be
deemed coincident with the interests of the holders of Common Stock.


                                      -33-
<PAGE>


     Section 28. SUCCESSORS. All the covenants and provisions of this Agreement
by or for the benefit of the Company or the Rights Agent shall bind and inure to
the benefit of their respective successors and assigns hereunder.

     Section 29. ACTIONS BY THE BOARD, ETC. The Board shall have the exclusive
power and authority to administer this Agreement and to exercise all rights and
powers specifically granted to the Board or to the Company, or as may be
necessary or advisable in the administration of this Agreement, including,
without limitation, the right and power to (i) interpret the provisions of this
Agreement, and (ii) make all determinations deemed necessary or advisable for
the administration of this Agreement (including a determination to redeem or not
redeem the Rights or to amend this Agreement). All such actions, calculations,
interpretations and determinations (including, for purposes of clause (y) below,
all omissions with respect to the foregoing) which are done or made by the Board
in good faith, shall (x) be final, conclusive and binding on the Company, the
Rights Agent, the holders of the Rights and all other parties, and (y) not
subject the Board to any liability to the holders of the Rights.

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

     Section 31. SEVERABILITY. If any term, provision, covenant or restriction
of this Agreement is held by a court of competent jurisdiction or other
authority to be invalid, void or unenforceable, the remainder of the terms,
provisions, covenants and restrictions of this Agreement shall remain in full
force and effect and shall in no way be affected, impaired or invalidated;
provided, however, that notwithstanding anything in this Agreement to the
contrary, if any such term, provision, covenant or restriction is held by such
court or authority to be invalid, void or unenforceable and the Board determines
in its good faith judgment that severing the invalid, void or unenforceable
language from this Agreement would adversely affect the purpose or effect of
this Agreement, the right of redemption set forth in Section 23 hereof shall be
reinstated and shall not expire until the close of business on the tenth day
following the date of such determination by the Board.

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

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


                                      -34-
<PAGE>


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




                                      -35-
<PAGE>



     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed and their respective corporate seals to be hereunto affixed and
attested, all as of the day and year first above written.

Attest:                                     TRANSKARYOTIC THERAPIES, INC.



By:  /s/ Philip Chase                       By: /s/ Daniel E. Geffken
   --------------------------------            --------------------------------
Name:    Philip Chase                      Name:    Daniel E. Geffken
     ------------------------------              ------------------------------
Title:                                      Title:  Vice President, Finance and
                                                    Chief Financial Officer
      -----------------------------               -----------------------------


Attest:                                     EQUISERVE TRUST COMPANY, N.A.



By: /s/ Geraldine Murray                    By:  /s/ Margaret Prentice
   --------------------------------            --------------------------------
Name:   Geraldine Murray                    Name:    Margaret Prentice
     ------------------------------              ------------------------------
Title:  Account Manager                     Title:   Managing Director
      -----------------------------               -----------------------------



                                      -36-
<PAGE>


                                     FORM OF

                           CERTIFICATE OF DESIGNATIONS

                                       OF

                  SERIES B JUNIOR PARTICIPATING PREFERRED STOCK

                                       OF

                          TRANSKARYOTIC THERAPIES, INC.

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


Transkaryotic Therapies, Inc., a corporation organized and existing under the
laws 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 at a meeting duly called and held on December 13, 2000:

RESOLVED: That pursuant to the authority granted to and vested in the Board of
Directors of the Corporation (hereinafter called the "Board") in accordance with
the provisions of the Certificate of Incorporation, as amended, the Board hereby
creates a series of Preferred Stock, $0.01 par value per share (the "Preferred
Stock"), of the Corporation and hereby states the designation and number of
shares, and fixes the relative rights, preferences and limitations thereof as
follows:

     SERIES B JUNIOR PARTICIPATING PREFERRED STOCK:

     Section 1. DESIGNATION AND AMOUNT. The shares of such series shall be
designated as "Series B Junior Participating Preferred Stock" (the "Series B
Preferred Stock") and the number of shares constituting the Series B Preferred
Stock shall be one million (1,000,000). Such number of shares may be increased
or decreased by resolution of the Board prior to issuance; PROVIDED, that no
decrease shall reduce the number of shares of Series B Preferred Stock to a
number less than the number of shares then outstanding plus the number of shares
reserved for issuance upon the exercise of outstanding options, rights or
warrants or upon the conversion of any outstanding securities issued by the
Corporation convertible into Series B 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
B Preferred Stock with respect to dividends, the holders of shares of Series B
Preferred Stock, in preference to the holders of Common Stock, par value $0.01
per share (the "Common Stock"), of the Corporation, and of any other junior
stock, shall be entitled to receive, when, as and if declared by the Board out
of funds of the Corporation legally available for the payment of dividends,
quarterly dividends payable in cash on the last day of each fiscal quarter of
the Corporation 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 B


                                      A-1
<PAGE>


Preferred Stock, in an amount per share (rounded to the nearest cent) equal to
the greater of (a) $10 or (b) subject to the provision for adjustment
hereinafter set forth, 1,000 times the aggregate per share amount of all cash
dividends, and 1,000 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 B 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, 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 B 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. In the event the Corporation shall at any time declare or pay any
dividend on the Series B Preferred Stock payable in shares of Series B Preferred
Stock, or effect a subdivision, combination or consolidation of the outstanding
shares of Series B Preferred Stock (by reclassification or otherwise than by
payment of a dividend in shares of Series B Preferred Stock) into a greater or
lesser number of shares of Series B Preferred Stock, then in each such case the
amount to which holders of shares of Series B Preferred Stock were entitled
immediately prior to such event under clause (b) of the first sentence of this
Section 2(A) shall be adjusted by multiplying such amount by a fraction, the
numerator of which is the number of shares of Series B Preferred Stock that were
outstanding immediately prior to such event and the denominator of which is the
number of shares of Series B Preferred Stock outstanding immediately after such
event.

     (B) The Corporation shall declare a dividend or distribution on the Series
B 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) and the Corporation shall pay such
dividend or distribution on the Series B Preferred Stock before the dividend or
distribution declared on the Common Stock is paid or set apart; 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 $10 per share on the
Series B 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 B 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 B Preferred Stock entitled to receive a quarterly dividend
and before such Quarterly Dividend Payment Date, in either of which events such
dividends shall begin to accrue and be cumulative


                                      A-2
<PAGE>


from such Quarterly Dividend Payment Date. Accrued but unpaid dividends shall
not bear interest. Dividends paid on the shares of Series B 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 may fix a record date
for the determination of holders of shares of Series B 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 B Preferred Stock
shall have the following voting rights:

     (A) Subject to the provision for adjustment hereinafter set forth, each
share of Series B Preferred Stock shall entitle the holder thereof to 1,000
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,
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 B
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. In the event the Corporation shall
at any time declare or pay any dividend on the Series B Preferred Stock payable
in shares of Series B Preferred Stock, or effect a subdivision, combination or
consolidation of the outstanding shares of Series B Preferred Stock (by
reclassification or otherwise than by payment of a dividend in shares of Series
B Preferred Stock) into a greater or lesser number of shares of Series B
Preferred Stock, then in each such case the number of votes per share to which
holders of shares of Series B Preferred Stock were entitled immediately prior to
such event shall be adjusted by multiplying such amount by a fraction, the
numerator of which is the number of shares of Series B Preferred Stock that were
outstanding immediately prior to such event and the denominator of which is the
number of shares of Series B Preferred Stock outstanding immediately after such
event.

     (B) Except as otherwise provided herein, in the Certificate of
Incorporation or by law, the holders of shares of Series B 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) (i) If at any time dividends on any Series B Preferred Stock shall be
in arrears in an amount equal to six quarterly dividends thereon, the holders of
the Series B Preferred Stock, voting as a separate series from all other series
of Preferred Stock and classes of capital stock, shall be entitled to elect two
members of the Board in addition to any Directors elected by any other series,
class or classes of securities and the authorized number of Directors will
automatically be increased by two. Promptly thereafter, the Board of the
Corporation shall, as soon as may be practicable, call a special meeting of
holders of Series B Preferred Stock for the purpose of electing such members of
the Board. Such special meeting shall in any event be held within 45 days of the
occurrence of such arrearage.


                                      A-3
<PAGE>


                  (ii) During any period when the holders of Series B Preferred
         Stock, voting as a separate series, shall be entitled and shall have
         exercised their right to elect two Directors, then, and during such
         time as such right continues, (a) the then authorized number of
         Directors shall be increased by two, and the holders of Series B
         Preferred Stock, voting as a separate series, shall be entitled to
         elect the additional Directors so provided for, and (b) each such
         additional Director shall not be a member of any existing class of the
         Board, but shall serve until the next annual meeting of stockholders
         for the election of Directors, or until his successor shall be elected
         and shall qualify, or until his right to hold such office terminates
         pursuant to the provisions of this Section 3(C).

                  (iii) A Director elected pursuant to the terms hereof may be
         removed with or without cause by the holders of Series B Preferred
         Stock entitled to vote in an election of such Director.

                  (iv) If, during any interval between annual meetings of
         stockholders for the election of Directors and while the holders of
         Series B Preferred Stock shall be entitled to elect two Directors,
         there is no such Director in office by reason of resignation, death or
         removal, then, promptly thereafter, the Board shall call a special
         meeting of the holders of Series B Preferred Stock for the purpose of
         filling such vacancy and such vacancy shall be filled at such special
         meeting. Such special meeting shall in any event be held within 45 days
         of the occurrence of such vacancy.

                  (v) At such time as the arrearage is fully cured, and all
         dividends accumulated and unpaid on any shares of Series B Preferred
         Stock outstanding are paid, and, in addition thereto, at least one
         regular dividend has been paid subsequent to curing such arrearage, the
         term of office of any Director elected pursuant to this Section 3(C),
         or his successor, shall automatically terminate, and the authorized
         number of Directors shall automatically decrease by two, the rights of
         the holders of the shares of the Series B Preferred Stock to vote as
         provided in this Section 3(C) shall cease, subject to renewal from time
         to time upon the same terms and conditions, and the holders of shares
         of the Series B Preferred Stock shall have only the limited voting
         rights elsewhere herein set forth.

     (D) Except as set forth herein, or as otherwise provided by law, holders of
Series B 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.


                                      A-4
<PAGE>


     Section 4. CERTAIN RESTRICTIONS.

     (A) Whenever quarterly dividends or other dividends or distributions
payable on the Series B 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 B Preferred Stock outstanding shall have
been paid in full, the Corporation shall not:

                  (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 B 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 B Preferred Stock, except dividends paid ratably on the Series B
         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
         B 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 B Preferred Stock; or

                  (iv) redeem or purchase or otherwise acquire for consideration
         any shares of Series B Preferred Stock, or any shares of stock ranking
         on a parity with the Series B Preferred Stock, except in accordance
         with a purchase offer made in writing or by publication (as determined
         by the Board) to all holders of such shares upon such terms as the
         Board, 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 B Preferred Stock
purchased or otherwise acquired by the Corporation in any manner whatsoever
shall be retired and cancelled 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.


                                      A-5
<PAGE>


     Section 6. LIQUIDATION, DISSOLUTION OR WINDING UP.

     (A) 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 B Preferred Stock unless, prior thereto, the holders of shares of Series
B Preferred Stock shall have received $1000 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 B
Preferred Stock shall be entitled to receive an aggregate amount per share,
subject to the provision for adjustment hereinafter set forth, equal to 1,000
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 B Preferred Stock, except distributions made ratably on the Series B
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.

     (B) Neither the consolidation, merger or other business combination of the
Corporation with or into any other corporation nor the sale, lease, exchange or
conveyance of all or any part of the property, assets or business of the
Corporation shall be deemed to be a liquidation, dissolution or winding up of
the Corporation for purposes of this Section 6.

     (C) 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, 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 B
Preferred Stock were entitled immediately prior to such event under the proviso
in clause (1) of paragraph (A) of this Section 6 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. In the event the Corporation shall
at any time declare or pay any dividend on the Series B Preferred Stock payable
in shares of Series B Preferred Stock, or effect a subdivision, combination or
consolidation of the outstanding shares of Series B Preferred Stock (by
reclassification or otherwise than by payment of a dividend in shares of Series
B Preferred Stock) into a greater or lesser number of shares of Series B
Preferred Stock, then in each such case the aggregate amount to which holders of
shares of Series B Preferred Stock were entitled immediately prior to such event
under the proviso in clause (1) of paragraph (A) of this Section 6 shall be
adjusted by multiplying such amount by a fraction, the numerator of which is the
number of shares of Series B Preferred Stock that were outstanding immediately
prior to such event and the denominator of which is the number of shares of
Series B Preferred Stock outstanding immediately after such event.

     Section 7. CONSOLIDATION, MERGER, ETC. Notwithstanding anything to the
contrary contained herein, 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 B
Preferred Stock shall at the same time be similarly exchanged or changed into an


                                      A-6
<PAGE>


amount per share, subject to the provision for adjustment hereinafter set forth,
equal to 1,000 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, 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 B
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. In
the event the Corporation shall at any time declare or pay any dividend on the
Series B Preferred Stock payable in shares of Series B Preferred Stock, or
effect a subdivision, combination or consolidation of the outstanding shares of
Series B Preferred Stock (by reclassification or otherwise than by payment of a
dividend in shares of Series B Preferred Stock) into a greater or lesser number
of shares of Series B Preferred Stock, then in each such case the amount set
forth in the first sentence of this Section 7 with respect to the exchange or
change of shares of Series B Preferred Stock shall be adjusted by multiplying
such amount by a fraction, the numerator of which is the number of shares of
Series B Preferred Stock that were outstanding immediately prior to such event
and the denominator of which is the number of shares of Series B Preferred Stock
outstanding immediately after such event.

     Section 8. NO REDEMPTION. The shares of Series B Preferred Stock shall not
be redeemable.

     Section 9. RANK. The Series B 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 Preferred Stock issued either before or after the
issuance of the Series B Preferred Stock, including, without limitation, the
Series A Convertible Preferred Stock, unless the terms of any such series shall
provide otherwise.

     Section 10. AMENDMENT. At such time as any shares of Series B Preferred
Stock are outstanding, the Certificate of Incorporation, as amended, 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 B Preferred Stock
so as to affect them adversely without the affirmative vote of the holders of at
least two-thirds of the outstanding shares of Series B Preferred Stock, voting
together as a single class.

     Section 11. FRACTIONAL SHARES. Series B Preferred Stock may be issued in
fractions of a share which shall entitle the holder, in proportion to such
holder's fractional shares, to exercise voting rights, receive dividends,
participate in distributions and have the benefit of all other rights of holders
of Series B Preferred Stock.


                                      A-7
<PAGE>


     IN WITNESS WHEREOF, this Certificate of Designations is executed on behalf
of the Corporation by its Vice President, Finance and Chief Financial Officer
this 13th day of December, 2000.

                                      TRANSKARYOTIC THERAPIES, INC.

                                      By:
                                             ---------------------------------
                                      Name:  Daniel E. Geffken
                                      Title: Vice President, Finance and Chief
                                             Financial Officer



                                      A-8
<PAGE>


                          [Form of Rights Certificate]

Certificate No. R-                                                ______ Rights

NOT EXERCISABLE AFTER DECEMBER 13, 2010 OR EARLIER IF REDEEMED OR EXCHANGED BY
THE COMPANY. THE RIGHTS ARE SUBJECT TO REDEMPTION AT $0.001 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. [THE RIGHTS REPRESENTED BY THIS RIGHTS CERTIFICATE ARE OR
WERE BENEFICIALLY OWNED BY A PERSON WHO WAS OR BECAME AN ACQUIRING PERSON OR AN
AFFILIATE OR ASSOCIATE OF AN ACQUIRING PERSON (AS SUCH TERMS ARE DEFINED IN THE
RIGHTS AGREEMENT). ACCORDINGLY, THIS RIGHTS CERTIFICATE AND THE RIGHTS
REPRESENTED HEREBY MAY BECOME NULL AND VOID IN THE CIRCUMSTANCES SPECIFIED IN
SECTION 7(e) OF SUCH AGREEMENT.](1)

                          TRANSKARYOTIC THERAPIES, INC.

                               Rights Certificate

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 December 13, 2000 (the "Rights Agreement"), between
Transkaryotic Therapies, Inc., a Delaware corporation (the "Company"), and
EquiServe Trust Company, N.A. (the "Rights Agent"), to purchase from the Company
after the Distribution Date (as such term is defined in the Rights Agreement)
and at any time prior to 5:00 p.m. (Boston time) on December 13, 2010 at the
office of the Rights Agent designated for such purpose, or its successors as
Rights Agent, one one-thousandth of a fully paid, non-assessable share of Series
B Junior Participating Preferred Stock (the "Preferred Stock") of the Company,
$0.01 par value per share, at a purchase price of $289 in cash per one
one-thousandth of a share (the "Purchase Price"), upon presentation and
surrender of this Rights Certificate with the Form of Election to Purchase and
related Certificate duly executed. The number of Rights evidenced by this Rights
Certificate (and the number of one one-thousandth of a share of Preferred Stock
which may be purchased upon exercise hereof) set forth above, and the Purchase
Price set forth above, are the number and Purchase Price as of the close of
business on December 13, 2000, based on the Preferred Stock as constituted at
such date. Capitalized terms used herein and not otherwise defined herein shall
have the meanings ascribed to such terms in the Rights Agreement.

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

(1) The portion of the legend in brackets shall be inserted only if applicable
and shall replace the preceding sentence.


                                      B-1
<PAGE>


Upon the occurrence of a Section 11(a)(ii) Event, if the Rights evidenced by
this Rights Certificate are beneficially owned by (i) an Acquiring Person or an
Affiliate or Associate of any such Acquiring Person (as such terms are defined
in the Rights Agreement), (ii) a transferee of any such Acquiring Person,
Associate or Affiliate who becomes a transferee after the Acquiring Person
becomes an Acquiring Person, or (iii) under certain circumstances specified in
the Rights Agreement, a transferee of a person who, concurrently with or after
such transfer, became an Acquiring Person, or an Affiliate or Associate of an
Acquiring Person, such Rights shall become null and void and no holder hereof
shall have any right with respect to such Rights from and after the occurrence
of such Section 11(a)(ii) Event.

As provided in the Rights Agreement, the Purchase Price and the number and kind
of shares of Preferred Stock or other securities which 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, including
Section 11(a)(ii) 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 hereunder of the
Rights Agent, the Company and the holders of the Rights Certificates, which
limitations of rights include the temporary suspension of the exercisability of
such Rights under the specific circumstances set forth in the Rights Agreement.
Copies of the Rights Agreement are on file at the principal offices of the
Company and are available upon written request to the Company.

This Rights Certificate, with or without other Rights Certificates, upon
surrender at the office of the Rights Agent designated for such purpose, with
the Form of Election and Certificate set forth on the reverse side duly
executed, may be exchanged for another Rights Certificate or Rights Certificates
of like tenor and date evidencing Rights entitling the holder to purchase a like
aggregate number of one one-thousandths of a share of Preferred Stock as the
Rights evidenced by the Rights Certificate or Rights Certificates surrendered
shall have entitled such holder to purchase. If this Rights Certificate shall be
exercised in part, the holder shall 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 may be redeemed by the Company at its option at a redemption price
of $0.001 per Right at any time prior to the earlier of (i) the close of
business on the tenth Business Day following the Stock Acquisition Date (or, if
the Stock Acquisition Date shall have occurred prior to the Record Date, the
close of business on the tenth Business Day following the Record Date) and (ii)
the Final Expiration Date.

Subject to the provisions of the Rights Agreement, the Company may, at its
option, at any time after a Section 11(a)(ii) Event, exchange all or part of the
Rights evidenced by this Certificate for shares of the Company's Common Stock or
for Preferred Stock (or shares of a class or series of the Company's preferred
stock having the same rights, privileges and preferences as the Preferred
Stock).


                                      B-2
<PAGE>


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

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

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

         WITNESS the facsimile signature of the proper officers of the Company
and its corporate seal.

                                               DATED AS OF ___________

ATTEST:                                     TRANSKARYOTIC THERAPIES, INC.


___________________________                 By:___________________________
      Secretary

                                            Title:_________________________


                                                  COUNTERSIGNED:

                                                  EQUISERVE TRUST COMPANY, N.A.

                                                  By:__________________________

                                                  Authorized Signature



                                      B-3
<PAGE>


                  [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 unto _________________________________________
__________________________________________________________________________

(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 ______________________ Attorney,
to transfer the within Rights Certificate on the books of the within-named
Company, with full power of substitution.

                                                  DATED:_______________________
                                                        SIGNATURE

Signature Guaranteed:

                                   Certificate

The undersigned hereby certifies that the Rights evidenced by this Rights
Certificate are not beneficially owned by, or being assigned to, an Acquiring
Person or an Affiliate or Associate thereof (as such terms are defined pursuant
to the Rights Agreement).

                                                  DATED:_______________________
                                                        SIGNATURE

Signature Guaranteed:

     (b) NOTICE

The signature to the foregoing Assignment and Certificate must correspond to the
name as written upon the face of this Rights Certificate in every particular,
without alteration or enlargement or any change whatsoever.



                                      B-4
<PAGE>


                          FORM OF ELECTION TO PURCHASE

                  (To be executed if holder desires to exercise

                 Rights represented by the Rights Certificate.)


To:           EquiServe Trust Company, N.A.


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

              Please insert social security

              or other identifying number __________________________________


_______________________________________________________________________________
                         (Please print name and address)
_______________________________________________________________________________

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

Please insert social security

or other identifying number  __________________________________________________

_______________________________________________________________________________
                         (Please print name and address)



                                                  _____________________________

                                                  _____________________________

                                                  DATED:_______________________
                                                        SIGNATURE



Signature Guaranteed:



                                      B-5
<PAGE>


                                   Certificate

     The undersigned hereby certifies by checking the appropriate boxes that:

     (1) the Rights evidenced by this Rights Certificate [ ] are [ ] are not
being exercised by or on behalf of a Person who is or was an Acquiring Person or
an Affiliate or Associate thereof (as such terms are defined pursuant to the
Rights Agreement);

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

                                                  DATED:_______________________
                                                        SIGNATURE

Signature Guaranteed:

                                     NOTICE

The signature to the foregoing Election to Purchase and Certificate must
correspond to the name as written upon the face of this Rights Certificate in
every particular, without alteration or enlargement or any change whatsoever.



                                      B-6
<PAGE>


                              SUMMARY OF RIGHTS TO

                            PURCHASE PREFERRED STOCK

On December 13, 2000, the Board of Directors of Transkaryotic Therapies, Inc.
(the "Company"), declared a dividend of one Right for each outstanding share of
the Company's Common Stock to stockholders of record at the close of business on
December 26, 2000 (the "Record Date"). Each Right entitles the registered holder
to purchase from the Company one one-thousandth of a share of Series B Junior
Participating Preferred Stock, $0.01 par value per share (the "Preferred
Stock"), at a Purchase Price of $289 in cash, subject to adjustment. The
description and terms of the Rights are set forth in a Rights Agreement dated as
of December 13, 2000 (the "Rights Agreement") between the Company and EquiServe
Trust Company, N.A., as Rights Agent.

Initially, the Rights are not exercisable and will be attached to all Common
Stock certificates representing shares then outstanding, and no separate Rights
Certificates will be distributed. The Rights will separate from the Common Stock
and a Distribution Date will occur upon the earlier of (i) 10 business days
following the first date of a public announcement that a person or group of
affiliated or associated persons (an "Acquiring Person") has acquired, or
obtained the right to acquire, beneficial ownership of 20% or more of the
outstanding shares of Common Stock (other than certain specified entities
affiliated with E.M. Warburg, Pincus & Co., LLC, which will have the right to
acquire beneficial ownership of up to 30% of the Company's Common Stock) (the
"Stock Acquisition Date"), or (ii) 10 business days following the commencement
of a tender offer or exchange offer that would result in a person or group
beneficially owning 20% or more of such outstanding shares of Common Stock
(other than certain specified entities associated with Warburg Pincus, which
will have the right to acquire beneficial ownership of up to 30% of the
Company's Common Stock). Under the Rights Plan, for all purposes, including
determining the specified percentage of Common Stock necessary to trigger a
Distribution Date, the Company's outstanding Series A Convertible Preferred
Stock shall be treated as if its holders had converted such shares into Common
Stock at the then applicable conversion rate. The Distribution Date may be
deferred by the Board of Directors. In addition, certain inadvertent
acquisitions will not trigger the occurrence of the Distribution Date. Until the
Distribution Date (or earlier redemption or expiration of the Rights), (i) the
Rights will be evidenced by the Common Stock certificates outstanding on the
Record Date, together with a Summary of Rights to be mailed to stockholders, or
by new Common Stock certificates issued after the Record Date which contain a
notation incorporating the Rights Agreement by reference, (ii) the Rights will
be transferred with and only with such Common Stock certificates; and (iii) the
surrender for transfer of any certificates for Common Stock outstanding (with or
without a copy of the Summary of Rights or such notation) will also constitute
the transfer of the Rights associated with the Common Stock represented by such
certificate.

The Rights are not exercisable until the Distribution Date and will expire upon
the close of business on December 13, 2010 (the "Final Expiration Date") unless
earlier redeemed or exchanged as described below. As soon as practicable after
the Distribution Date, separate Rights Certificates will be mailed to holders of
record of the Common Stock as of the close of business on the Distribution Date
and, thereafter, the separate Rights Certificates alone will represent the
Rights. Except as otherwise determined by the Board of Directors, and except for


                                      C-1
<PAGE>


shares of Common Stock issued upon exercise, conversion or exchange of then
outstanding options, convertible or exchangeable securities or other contingent
obligations to issue shares or pursuant to any employee benefit plan or
arrangement, only shares of Common Stock issued prior to the Distribution Date
will be issued with Rights.

In the event that any Person becomes an Acquiring Person, then, promptly
following the first occurrence of such event, each holder of a Right (except as
provided below and in Section 7(e) of the Rights Agreement) shall thereafter
have the right to receive, upon exercise, that number of shares of Common Stock
of the Company (or, in certain circumstances, cash, property or other securities
of the Company) which equals the exercise price of the Right divided by 50% of
the current market price (as defined in the Rights Agreement) per share of
Common Stock at the date of the occurrence of such event. However, Rights are
not exercisable following such event until such time as the Rights are no longer
redeemable by the Company as described below. Notwithstanding any of the
foregoing, following the occurrence of such event, all Rights that are, or
(under certain circumstances specified in the Rights Agreement) were,
beneficially owned by any Acquiring Person will be null and void. The event
summarized in this paragraph is referred to as a "Section 11(a)(ii) Event."

For example, at an exercise price of $300.00 per Right, each Right not owned by
an Acquiring Person (or by certain related parties) following a Section
11(a)(ii) Event would entitle its holder to purchase for $300.00 such number of
shares of Common Stock (or other consideration, as noted above) as equals
$300.00 divided by one-half of the current market price (as defined in the
Rights Agreement) of the Common Stock. Assuming that the Common Stock had a
market price of $50.00 per share at such time, the holder of each valid Right
would be entitled to purchase twelve shares of Common Stock, having a market
value of 12 x $50, or $600.00, for $300.00.

In the event that, at any time after any Person becomes an Acquiring Person, (i)
the Company is consolidated with, or merged with and into, another entity and
the Company is not the surviving entity of such consolidation or merger or if
the Company is the surviving entity, but shares of its outstanding Common Stock
are changed or exchanged for stock or securities (of any other person) or cash
or any other property, or (ii) more than 50% of the Company's assets or earning
power is sold or transferred, each holder of a Right (except Rights which
previously have been voided as set forth above) shall thereafter have the right
to receive, upon exercise, that number of shares of common stock of the
acquiring company which equals the exercise price of the Right divided by 50% of
the current market price (as defined in the Rights Agreement) of such common
stock at the date of the occurrence of the event. The events summarized in this
paragraph are referred to as "Section 13 Events." A Section 11(a)(ii) Event and
Section 13 Events are collectively referred to as "Triggering Events."

For example, at an exercise price of $300.00 per Right, each valid Right
following a Section 13 Event would entitle its holder to purchase for $300.00
such number of shares of common stock of the acquiring company as equals $300.00
divided by one-half of the current market price (as defined in the Rights
Agreement) of such common stock. Assuming that such common stock had a market
price of $50.00 per share at such time, the holder of each valid Right would be
entitled to purchase twelve shares of common stock of the acquiring company,
having a market value of 12 x $50, or $600.00, for $300.00.


                                      C-2
<PAGE>


At any time after the occurrence of a Section 11(a)(ii) Event, when no person
owns a majority of the Common Stock, the Board of Directors of the Company may
exchange the Rights (other than Rights owned by such Acquiring Person which have
become void), in whole or in part, at an exchange ratio of one share of Common
Stock, or one one-thousandth of a share of Preferred Stock (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).

The Purchase Price payable, and the number of units of Preferred Stock 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
Stock, (ii) if holders of the Preferred Stock are granted certain rights or
warrants to subscribe for Preferred Stock or convertible securities at less than
the then-current market price (as defined in the Rights Agreement) of the
Preferred Stock, or (iii) upon the distribution to holders of the Preferred
Stock of evidences of indebtedness or assets (excluding regular periodic cash
dividends paid out of earnings or retained earnings) or of subscription rights
or warrants (other than those referred to above). The number of Rights
associated with each share of Common Stock is also subject to adjustment in the
event of a stock split of the Common Stock or a stock dividend on the Common
Stock payable in Common Stock or subdivisions, consolidations or combinations of
the Common Stock occurring, in any such case, prior to the Distribution Date.

With certain exceptions, no adjustment in the Purchase Price will be required
until cumulative adjustments amount to at least 1% of the Purchase Price. No
fractional shares of Preferred Stock (other than fractions which are integral
multiples of one one-thousandth of a share of Preferred Stock) will be issued
and, in lieu thereof, an adjustment in cash will be made based on the market
price of the Preferred Stock on the last trading date prior to the date of
exercise.

Preferred Stock purchasable upon exercise of the Rights will not be redeemable.
Each share of Preferred Stock will be entitled to receive, when, as and if
declared by the Board of Directors, a minimum preferential quarterly dividend
payment of $10 per share or, if greater, an aggregate dividend of 1,000 times
the dividend declared per share of Common Stock. In the event of liquidation,
the holders of the Preferred Stock will be entitled to a minimum preferential
liquidation payment of $1,000 per share, plus an amount equal to accrued and
unpaid dividends, and will be entitled to an aggregate payment of 1,000 times
the payment made per share of Common Stock. Each share of Preferred Stock will
have 1,000 votes, voting together with the Common Stock. In the event of any
merger, consolidation or other transaction in which Common Stock is changed or
exchanged, each share of Preferred Stock will be entitled to receive 1,000 times
the amount received per share of Common Stock. These rights are protected by
customary antidilution provisions. Because of the nature of the Preferred
Stock's dividend, liquidation and voting rights, the value of one one-thousandth
of a share of Preferred Stock purchasable upon exercise of each Right should
approximate the value of one share of Common Stock.

At any time prior to the earlier of (i) the tenth Business Day (or such later
date as may be determined by the Board of Directors of the Company) after the
Stock Acquisition Date, or (ii) the Final Expiration Date, the Company may
redeem the Rights in whole, but not in part, at a price of $0.001 per Right (the
"Redemption Price"), payable in cash or stock. Immediately upon


                                      C-3
<PAGE>


the redemption of the Rights or such earlier time as established by the Board in
the resolution ordering the redemption of the Rights, the Rights will terminate
and the only right of the holders of Rights will be to receive the Redemption
Price. The Rights may also be redeemable following certain other circumstances
specified in the Rights Agreement.

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. While the distribution of the Rights will not be
taxable to stockholders or to the Company, stockholders may, depending upon the
circumstances, recognize taxable income in the event that the Rights become
exercisable for Common Stock (or other consideration) of the Company or for
common stock of the acquiring company as set forth above.

Any provision of the Rights Agreement, other than the redemption price, may be
amended by the Board prior to such time as the Rights are no longer redeemable.
Once the Rights are no longer redeemable, the Board's authority to amend the
Rights is limited to correcting ambiguities or defective or inconsistent
provisions in a manner that does not adversely affect the interest of holders of
Rights.

The Rights are intended to protect the stockholders of the Company in the event
of an unfair or coercive offer to acquire the Company and to provide the Board
with adequate time to evaluate unsolicited offers. The Rights may have
anti-takeover effects. The Rights will cause substantial dilution to a person or
group that attempts to acquire the Company without conditioning the offer on a
substantial number of Rights being acquired. The Rights, however, should not
affect any prospective offeror willing to make an offer at a fair price and
otherwise in the best interests of the Company and its stockholders, as
determined by a majority of the Board. The Rights should not interfere with any
merger or other business combination approved by the Board.

A copy of the Rights Agreement has been filed with the Securities and Exchange
Commission as an Exhibit to the Company's Current Report on Form 8-K dated
December 14, 2000. 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 incorporated herein by reference.



                                      C-4