STOCK OPTION AGREEMENT


     THIS STOCK OPTION AGREEMENT is made and entered into as of December 10,
2000 (the "Agreement") by and between Shire Pharmaceuticals Group Plc, a company
registered in England under registry number 2883758 ("Shire"), and BioChem
Pharma Inc., a corporation incorporated under the laws of Canada ("BioChem"),
with respect to the following facts:

                                   WITNESSETH:

     A. Concurrently with the execution and delivery of this Agreement, Shire,
BioChem and 3829341 Canada Inc., a corporation incorporated under the laws of
Canada and an indirect wholly-owned subsidiary of Shire ("Exchangeco"), are
entering into a merger agreement (the "Merger Agreement"), which provides that,
among other things, upon the terms and subject to the conditions thereof, Shire
and BioChem will enter into a business combination transaction (the
"Arrangement").

     B. As a condition to Shire's willingness to enter into the Merger
Agreement, Shire has requested that BioChem agree, and BioChem has so agreed, to
grant to Shire an option to acquire BioChem Common Shares ("BioChem Shares"),
upon the terms and subject to the conditions set forth herein.

     C. Capitalized terms used and not otherwise defined herein that are defined
in the Merger Agreement shall have the respective meanings ascribed thereto in
the Merger Agreement.

     In consideration of the foregoing and the respective representations,
warranties and covenants set forth in this Agreement, and intending to be
legally bound hereby and thereby, the parties agree hereto as follows:

     1. Grant of Option.

     (a) Subject to the terms and conditions set forth herein, including receipt
of all regulatory approvals to the granting of the Option (including approvals,
as the case may be, of the TSE (collectively, the "Stock Exchange")), BioChem
hereby grants to Shire an irrevocable option (the "Option") to acquire up to
19.9% of the outstanding BioChem Shares as of December 8, 2000 (on an undiluted
basis) (the "Option Shares"), in the manner set forth below at a price (the
"Exercise Price") of US$37.00 per Option Share, payable in cash.

     (b) In the event Shire receives official notice that all regulatory
approvals necessary in respect of the granting of the Option, including approval
of the relevant Stock Exchange, will not be issued or granted, the Option and
this Agreement


<PAGE>
                                      -2-


shall be, and shall be deemed to be, one stock appreciation right ("SAR") with
respect to the Option Shares. At the request and upon notice by Shire at any
time during the period during which the Option is exercisable, BioChem (or any
successor entity thereof) shall purchase from Shire the SAR, at a price equal to
the difference between the "Market/Tender Offer Price" for BioChem Shares as of
the date Shire gives notice of its intent to exercise its rights under this
Section and the Exercise Price, multiplied by the number of BioChem Shares
purchasable pursuant to the Option. For purposes of this Agreement,
"Market/Tender Offer Price" means the higher of (A) the highest price per share
offered as of such date pursuant to any Acquisition Proposal which was made
prior to such date and not terminated or withdrawn as of such date and (B) the
highest closing sale price of BioChem Shares on the Nasdaq during the twenty
(20) trading days ending on the trading day immediately preceding such date. For
purposes of determining the highest price offered pursuant to any Acquisition
Proposal which involves consideration other than cash, the value of such
consideration shall be equal to the higher of (x) if securities of the proponent
of the same class as such consideration are traded on any national securities
exchange or by any registered securities association, a value based on the
closing sale price for such securities on their principal trading market on such
date and (y) the value ascribed to such consideration by the proponent of such
Acquisition Proposal, or if no such value is ascribed, a value determined in
good faith by the board of directors of BioChem.

     2. Exercise of Option; Maximum Proceeds.

     (a) The Option may be exercised by Shire, in whole or in part, at any time
and from time to time, immediately upon the occurrence of any event under
Section 7.2 of the Merger Agreement requiring BioChem to pay to Shire the amount
specified therein (the "Exercise Event"). In the event Shire wishes to exercise
the Option, Shire shall deliver to BioChem a written notice (each an "Exercise
Notice") specifying the total number of Option Shares it wishes to acquire and
pay the Exercise Price by certified cheque or wire transfer. Each closing of a
purchase of Option Shares (a "Closing") shall occur on a date and at a time
prior to the expiration of the Option designated by Shire in an Exercise Notice
delivered at least two Business Days prior to the date of such Closing, which
Closing shall be held at the offices of Stikeman Elliott, 1155 Rene-Levesque
Blvd. West, 40th Floor, Montreal (Quebec).

     (b) The Option shall expire upon the earliest to occur of (i) the Effective
Date, or (ii) the termination of the Merger Agreement pursuant to Article VII
thereof (other than a termination in connection with which Shire is or could in
time become entitled to any payments as specified in Section 7.2 thereof), or
(iii) 180 days after the date on which the Merger Agreement is terminated and
Shire has become entitled to a payment as specified in Section 7.2 thereof;
provided, however, that if the Option cannot be exercised by reason of any
applicable Laws, or because any applicable waiting period


<PAGE>
                                      -3-


related to issuance of the Option Shares under any applicable Laws shall not
have expired or been terminated, then the Option shall not terminate until the
tenth Business Day after such impediment to exercise shall have been removed or
shall have become final and not subject to appeal.

     (c) If Shire receives an amount pursuant to Section 7.2 of the Merger
Agreement which, when aggregated with gross proceeds received by Shire in
connection with any sales or other dispositions of Option Shares, less
reasonable and customary commissions paid in connection with such sales or
dispositions and any dividends received by Shire declared on Option Shares,
exceeds the sum of (x) US$120,000,000 plus (y) the Exercise Price multiplied by
the number of BioChem Shares purchased by Shire pursuant to the Option, then all
gross proceeds to Shire in excess of such sum shall be remitted by Shire to
BioChem or deducted from the payment to be made by BioChem pursuant to Section 1
(b) hereof.

     3. Conditions to Closing.

     The obligation of BioChem to issue Option Shares to Shire hereunder is
subject to the conditions that (a) all filings and declarations required to be
made, all authorizations, consents, orders and approvals required to be obtained
in connection with the grant of the Option and the issue of the Option Shares
(including the approval of the relevant Stock Exchange), and all waiting periods
required to expire or be terminated, pursuant to a requirement of any
Governmental Entity or applicable Law (including, without limitation the HSR Act
or the CA, as the case may be) shall have been made or obtained or shall have
expired or been terminated, in each case in connection with the exercise of the
Option hereunder; and (b) no preliminary or permanent injunction or other order
by any court of competent jurisdiction (or similar order from any Canadian, US
or UK securities authority) prohibiting or otherwise restraining such issuance
shall be in effect. It is understood and agreed that at any time during which
the Option is exercisable, the parties will use their respective commercial
reasonable efforts to satisfy all conditions to Closing, so that a Closing may
take place as promptly as practicable, and in any event, prior to consummation
of a tender or exchange offer or take-over bid for shares of BioChem capital
stock.

     4. Closing.

     At each Closing, (a) BioChem shall deliver to Shire a single certificate in
definitive form representing the number of BioChem Shares designated by Shire in
its Exercise Notice, such certificate to be registered in the name of Shire and
to bear the legend set forth in Section 10 hereof, against delivery of (b)
payment by Shire to BioChem of the aggregate purchase price for the BioChem
Shares so designated and being purchased by delivery of a certified cheque, bank
draft or wire transfer.


<PAGE>
                                      -4-


     5. Representations and Warranties of BioChem.

     BioChem represents and warrants to Shire that: (a) BioChem is a corporation
duly incorporated, validly existing and in good standing under the laws of
Canada and has full corporate power and authority to execute and deliver this
Agreement and to carry out its obligations hereunder; (b) the execution and
delivery of this Agreement by BioChem and consummation by BioChem of the
transactions contemplated hereby have been duly and validly authorized by all
necessary corporate action on the part of BioChem, and no other corporate
proceedings on the part of BioChem are necessary to authorize this Agreement or
any of the transactions contemplated hereby; (c) this Agreement has been duly
and validly executed and delivered by BioChem, constitutes a legal, valid and
binding obligation of BioChem and, assuming this Agreement constitutes a legal,
valid and binding obligation of Shire, is enforceable against BioChem in
accordance with its terms, except as enforceability may be limited by bankruptcy
and other laws affecting the rights and remedies of creditors generally and
general principles of equity; (d) except for any filings required under the CA
and the approval of the relevant Stock Exchange, BioChem has taken (or will in a
timely manner take) all necessary corporate and other action to authorize and
reserve for issuance and to permit it to issue upon exercise of the Option, and
at all times from the date hereof until the termination of the Option will have
reserved for issuance, a sufficient number of unissued BioChem Shares for Shire
to exercise the Option in full upon payment to BioChem of the Exercise Price in
connection therewith and will take all necessary corporate or other action to
authorize and reserve for issuance all additional BioChem Shares or other
securities which may be issuable pursuant to Section 9 upon exercise of the
Option and payment of the Exercise Price, all of which, upon their issuance and
delivery in accordance with the terms of this Agreement, will be validly issued,
fully paid and nonassessable; (e) upon delivery of the BioChem Shares and any
other securities to Shire upon exercise of the Option and payment of the
Exercise Price, Shire will acquire such BioChem Shares or other securities free
and clear of all material claims, liens, charges, encumbrances and security
interests of any kind or nature whatsoever, excluding those imposed by Shire;
(f) the execution and delivery of this Agreement by BioChem do not, and the
performance of this Agreement by BioChem will not, (i) conflict with the
articles of incorporation or bylaws of BioChem, (ii) assuming that the consent
approvals, authorizations, permits, filings and notifications referred to in
subsection 5d) are obtained or made as applicable, violate any order applicable
to BioChem or any of its Subsidiaries or by which they or any of their property
is bound or affected, or (iii) result in any breach of or constitute a default
(or an event which with notice or lapse of time or both would become a default)
under, or give rise to any right of termination, amendment, acceleration or
cancellation of, or result in the creation of a lien or encumbrance on any of
the property or assets of BioChem or any of its Subsidiaries pursuant to, any
contract or agreement to which BioChem or any of its Subsidiaries is a party or
by which BioChem or any of its Subsidiaries or any of their property is bound or
affected, except, in the case of clauses (ii) and (iii) above, for violations,
conflicts,


<PAGE>
                                      -5-


breaches, defaults, rights of termination, amendment, acceleration or
cancellation, liens or encumbrances which would not, in the aggregate, have a
Material Adverse Effect on BioChem; and (g) except as described in Section
3.2(c) of the Merger Agreement, the execution and delivery of this Agreement by
BioChem does not, and the performance of this Agreement by BioChem will not,
require any consent, approval, authorization or permit of, or filing with, or
notification to, any Governmental Entity, except pursuant to the CA, the HSR
Act, the rules and regulations of the Stock Exchange, the Canadian Securities
Laws, the applicable US and UK securities laws or other applicable Regulatory
Laws, as the case may be.

     6. Representations and Warranties of Shire.

     Shire represents and warrants to BioChem that: (a) Shire is a corporation
duly incorporated and validly existing under the laws of England, and has full
corporate power and authority to execute and deliver this Agreement and to carry
out its obligations hereunder; (b) the execution and delivery of this Agreement
by Shire and the consummation by Shire of the transactions contemplated hereby
have been duly and validly authorized by all necessary corporate action on the
part of Shire and no other corporate proceedings on the part of Shire are
necessary to authorize this Agreement or any of the transactions contemplated
hereby; (c) this Agreement has been duly and validly executed and delivered by
Shire, constitutes a legal, valid and binding obligation of Shire and, assuming
this Agreement constitutes a legal, valid and binding obligation of BioChem, is
enforceable against Shire in accordance with its terms, except as enforceability
may be limited by bankruptcy and other laws affecting the rights and remedies of
creditors generally and general principles of equity; (d) the execution and
delivery of this Agreement by Shire do not, and the performance of this
Agreement by Shire will not, (i) conflict with certificate of incorporation or
bylaws of Shire, (ii) violate any order applicable to Shire or any of its
subsidiaries or by which they or any of their property is bound or affected, or
(iii) result in any breach of or constitute a default (or an event which with
notice or lapse of time or both would become a default) under, or give rise to
any right of termination, amendment, acceleration or cancellation of, or result
in the creation of a lien or encumbrance on any of the property or assets of
Shire or any of its Subsidiaries pursuant to, any contract or agreement to which
Shire or any of its Subsidiaries is a party or by which Shire or any of its
Subsidiaries or any of their property is bound or affected, except, in the case
of clauses (ii) and (iii) above, for violations, conflicts, breaches, defaults,
rights of termination, amendment, acceleration or cancellation, liens or
encumbrances which would not, in the aggregate, have a Material Adverse Effect
on Shire; (g) the execution and delivery of this Agreement by Shire does not,
and the performance of this Agreement by Shire will not, require any consent,
approval, authorization or permit of, or filing with or notification to, any
Governmental Entity, except pursuant to the HSR Act, the CA or other applicable
Regulatory Laws, as the case may be; and (h) any BioChem Shares acquired upon
exercise of the Option will


<PAGE>
                                      -6-


not be acquired by Shire with a view to the public distribution thereof and
Shire will not sell or otherwise dispose of such shares in violation of
applicable law or this Agreement.

     7. Registration Rights.

     (a) In the event that Shire desires to sell any of the Option Shares within
two years after the first exercise of the Option and requests in writing to
BioChem that BioChem register such Option Shares under the Securities Act or
qualify such Option Shares for resale under applicable Canadian securities laws,
unless in the opinion of counsel to BioChem (which opinion shall be reasonably
satisfactory to Shire and its counsel) such registration under the Securities
Act or qualification under applicable Canadian securities laws is not required
in order to lawfully sell and distribute such Option Shares in the manner
contemplated by Shire, BioChem shall cooperate with Shire and any underwriters
in registering or qualifying of such Option Shares for resale, including,
without limitation, promptly filing a registration statement and/or prospectus
which complies with the requirements of applicable U.S. federal and state
securities laws and/or Canadian federal, provincial and territorial securities
laws, as the case may be, and entering into and complying with an underwriting
agreement with such underwriters upon such terms and conditions as are
customarily contained in underwriting agreements with respect to secondary
distributions; (i) provided, however, that BioChem shall not be required to file
more than two registration statements which are declared effective and/or
prospectuses hereunder and shall be entitled to delay the filing or
effectiveness of any registration statement and/or prospectus for up to 120
consecutive days in any 12-month period if the offering would, in the judgment
of the Board of Directors of BioChem, require premature disclosure of any
material corporate development or otherwise materially interfere with or
materially adversely affect any pending or proposed offering of securities of
BioChem, acquisition or divestiture or any other material transaction involving
BioChem or any of its subsidiaries and (ii) provided, however, that BioChem
shall not be required, with respect to an underwritten secondary offering, to
file a registration statement or a prospectus upon obtention from an investment
banking firm of nationally recognized standing (the "Manager") of a certificate
stating that, in the good faith belief of the Manager, based on the then
prevailing market condition, it will not be able to sell the Option Shares at a
per share price equal to at least 80% of the per share average of the closing
sale prices of BioChem's Shares on the TSE or the Nasdaq. Shire agrees to use
its reasonable commercial efforts to cause, and to use its commercial efforts to
cause any underwriters of any sale or other disposition to cause, any sale or
other disposition pursuant to such registration statement and/or prospectus to
be effected on a widely distributed basis so that upon consummation thereof no
purchaser or transferee will own beneficially more than (3%) of the
then-outstanding BioChem Shares.

     (b) If Option Shares are registered or qualified pursuant to the provisions
of this Section 8, BioChem agrees (i) to furnish copies of the registration

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                                      -7-


statement and/or prospectus relating to the Option Shares covered thereby in
such numbers as Shire may from time to time reasonably request and (ii) if any
event shall occur as a result of which it becomes necessary to amend or
supplement any registration statement or prospectus, to prepare and file under
the applicable securities laws such amendments and supplements as may be
necessary to keep available for at least 120 days a prospectus covering the
Option Shares meeting the requirements of such securities laws, and to furnish
Shire with such numbers of copies of the registration statement and prospectus,
as amended or supplemented, as may reasonably be requested. BioChem shall bear
the cost of the registration or qualification, including but nor limited to, all
registration and filing fees, printing expenses, and fees and disbursements of
its counsel and accountants for BioChem, and Shire shall pay the fees and
disbursement s of its counsel and the underwriting fees and commissions
applicable to the Option Shares sold by Shire. BioChem shall indemnify and hold
harmless Shire, its affiliates and their respective officers and directors from
and against any and all losses, claims, damages, liabilities and expenses
arising out of or based upon any statements contained in or omissions or alleged
omissions from, each registration statement or prospectus (or any amendment
thereto) filed pursuant to this paragraph; provided, however, that this
provision shall not apply to any loss, liability, claim, damage or expense to
the extent it arises out of any untrue statement or omission made in reliance
upon and in conformity with written information furnished by BioChem by Shire,
its affiliates and its officers and other representatives expressly for use in
any registration statement or prospectus (or any amendment thereto) filed
pursuant to this paragraph. BioChem shall also indemnify and hold harmless each
underwriter and each person who controls any underwriter against any and all
losses, claims, damages, liabilities and expenses arising out of or based upon
any statement contained in or omissions or alleged omissions from, each
registration statement or prospectus (or any amendment thereto) filed pursuant
to this Section 8.

     9. Adjustment Upon Changes in Capitalization; Rights Plans.

     (a) If any change shall occur in the BioChem Shares by reason of stock
dividends, stock splits, reverse stock splits, mergers, amalgamations (other
than the Arrangement), recapitalizations, combinations, exchanges of shares and
the like, then (i) the type and number of shares or securities subject to the
Option and (ii) the Exercise Price shall be adjusted appropriately, and proper
provision shall be made in the agreements governing such transaction so that
Shire shall receive, upon exercise of the Option, the number and class of shares
or other securities or property that Shire would have received in respect of the
BioChem Shares if the Option had been exercised immediately prior to such change
or the record date therefor, as applicable.

     (b) (i) In the event that BioChem enters into an agreement (A) to
amalgamate with or merge into any Person, other than Shire or any Subsidiary of
Shire (each an "Excluded Person"), and BioChem is not the successor corporation
of such


<PAGE>
                                      -8-


amalgamation or merger, (B) to permit any Person, other than an Excluded Person,
to merge into BioChem and BioChem shall be the successor corporation, but, in
connection with such merger, the then outstanding BioChem Common Shares shall be
changed into or exchanged for stock or other securities of any other Person or
cash or any other property or the then outstanding BioChem Common Shares shall
after such merger represent less than 50% of the outstanding voting securities
of the merged or acquiring company, or (C) to sell or otherwise transfer all or
substantially all of its assets to any Person, then, and in each such case, the
agreement governing such transaction shall make proper provision so that, unless
earlier exercised by Shire, the Option shall, upon the consummation of any such
transaction and upon the terms and conditions set forth herein, be converted
into, or exchanged for, an option with identical terms appropriately adjusted to
acquire the number and class of shares or other securities or property that
Shire would have received in respect of BioChem Common Shares if the Option had
been exercised immediately prior to such amalgamation, merger, sale, or
transfer, on the record date therefor, as applicable, and make any other
necessary adjustments; provided, however, that if such a conversion or exchange
cannot, because of applicable Law be the same as the Option, such terms shall be
as similar as possible and in no event less advantageous to Shire than the
Option.

     (ii) In addition to any other restrictions or covenants, BioChem agrees
that it shall not enter or agree to enter into any transaction described in this
Section 9(b) unless the Acquiring Corporation (as hereinafter defined) and any
Person that controls the Acquiring Corporation assume in writing all the
obligations of BioChem hereunder and agree for the benefit of Shire to comply
with this Section 9.

     (iii) For purposes of this Section 9(b), the term "Acquiring Corporation"
shall mean (x) the successor Person of an amalgamation or merger with BioChem
(if other than BioChem), (y) BioChem in an amalgamation or merger in which
BioChem is the successor Person, and (z) the transferee of all or substantially
all of BioChem's assets.

     10. Restrictive Legends.

     Each certificate representing Option Shares issued to Shire hereunder shall
include a legend in substantially the following form:

     THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
     UNDER THE SECURITIES ACT OF 1933, OR QUALIFIED FOR DISTRIBUTION TO THE
     PUBLIC PURSUANT TO APPLICABLE CANADIAN SECURITIES LAWS OR UK SECURITIES
     LAWS, AND MAY BE REOFFERED OR SOLD ONLY IF SO REGISTERED OR QUALIFIED OR IF
     AN EXEMPTION FROM SUCH REGISTRATION(S) OR REQUIREMENT TO FILE A PROSPECTUS
     IS AVAILABLE. SUCH


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                                      -9-


     SECURITIES ARE ALSO SUBJECT TO ADDITIONAL RESTRICTIONS ON TRANSFER AS SET
     FORTH IN THE STOCK OPTION AGREEMENT, DATED AS OF DECEMBER 10, 2000, A COPY
     OF WHICH MAY BE OBTAINED FROM THE ISSUER.

     Certificates representing shares sold in a registered public offering
pursuant to Section 8 shall not be required to bear the legend set forth in this
Section 10.

     11. Listing and HSR and Regulatory Approvals

     BioChem, upon the request of Shire, shall promptly file an application to
list the BioChem Shares to be acquired upon exercise of the Option on the Stock
Exchange and shall use its reasonable commercial efforts to obtain approval of
such listings as soon as practicable. Promptly after a request by Shire, BioChem
shall file Notification and Report Forms under the CA with the Competition
Bureau and make all filings required under the HSR Act. BioChem shall use all
its best reasonable efforts to respond as promptly as practicable to any
inquiries received from the Competition Bureau or in response to filings under
the HSR Act for additional information or documentation.

     12. Waiver of Voting Rights.

     Shire agrees that it shall have no voting rights, and shall not exercise or
permit to be exercised any voting rights in any circumstances, in respect of the
Option or the Option Shares unless, until, and only to the extent that the
Option has been exercised and the Exercise Price has actually been paid to
BioChem.

     13. Binding Effect.

     This Agreement shall be binding upon and inure to the benefit of the
parties hereto and their respective successors and permitted assigns. This
Agreement is not intended to confer any rights or remedies upon any Person other
than the parties hereto. Any shares sold by a party in compliance with the
provisions of Section 8 hereof shall, upon consummation of such sale, be free of
the restrictions imposed with respect to such shares by this Agreement and any
transferee of such shares shall not be entitled the rights of the transferor
under this Agreement.

     14. Specific Performance.

     Each of the parties hereto recognizes and acknowledges that a breach by it
of any covenants or agreements contained in this Agreement will cause the other
party to sustain damages for which it would not have an adequate remedy at law
for money damages. Therefore, in the event of any such breach, the aggrieved
party shall be entitled to the remedy of specific performance of such covenants
and agreements and injunctive and


<PAGE>
                                      -10-


other equitable relief in addition to any other remedy to which it may be
entitled, at law or in equity.

     15. Entire Agreement.

     This Agreement and the Merger Agreement, including the exhibits and
schedules thereto and the documents and instruments referred to therein embody
the entire agreement and understanding of the parties hereto in respect of the
subject matter contained herein. There are no representations, promises,
warranties, covenants, or undertakings, other than those expressly set forth or
referred to herein and therein.

     16. Further Assurances.

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

     17. Severability.

     In case any one or more of the provisions contained in this Agreement
should be finally determined to be invalid, illegal or unenforceable in any
respect against a party hereto, it shall be adjusted if possible to effect the
intent of the parties. In any event, the validity, legality and enforceability
of the remaining provisions contained herein shall not in any way be affected or
impaired thereby, and such invalidity, illegality or unenforceability shall only
apply as to such party in the specific jurisdiction where such final
determination shall have been made.

     18. Notices.

     All notices and other communications hereunder shall be in writing and
shall be delivered personally, by overnight courier or similar means or sent by
facsimile with written confirmation of receipt, to the parties at the addresses
specified below (or at such other address for a party as shall be specified by
like notice). Any such notice shall be effective upon receipt, if personally
delivered, or on the next business day following transmittal, if sent by
facsimile. Notices shall be delivered as follows:


<PAGE>
                                      -11-


         (a)      if to Shire, to:

                           Shire Pharmaceuticals Group Plc
                           East Anton Andover
                           Hampshire, England
                           England SP10 5RG

                           Fax: 012 64 334 658
                           Attention: Rolf Stahel
                           with copies to:

                           McCarthy Tetrault
                           1170 Peel Street
                           Montreal, Quebec
                           H3B 4S8

                           Fax: (514) 397-4235
                           Attention: Benjamin H. Silver

         (b)      if to BioChem to:

                           Biochem Pharma Inc.
                           275 Armand-Frappier Blvd
                           Laval, Quebec
                           Canada   H7V 4A7

                           Fax: (450) 978-7899
                           Attention:  Francesco Bellini

                           with a copy to:

                           Stikeman Elliott
                           1155 Rene-Levesque Blvd West
                           Suite 4000
                           Montreal, Quebec
                           H3B 3V2

                           Fax: (514) 397-3222
                           Attention:  Jean Marc Huot


<PAGE>
                                      -12-


     19. Governing Law.

     This Agreement shall be governed and construed in accordance with the laws
of the Province of Quebec and the federal laws of Canada applicable therein
(without giving effect to choice of law principles thereof).

     20. Counterparts.

     This Agreement may be executed in two or more counterparts, each of which
shall be deemed to be an original, but both of which together shall constitute
one and the same instrument.

     21. Expenses.

     Except as otherwise expressly provided herein or in the Merger Agreement,
all costs, and expenses incurred in connection with the transactions
contemplated by this Agreement shall be paid by the party incurring such
expenses.

     22. Amendments; Waiver.

     This Agreement may be amended, modified or supplemented only by written
agreement of the parties. The terms and conditions hereof may be waived only by
an instrument in writing signed by the party granting such waiver, but such
waiver or failure to insist upon strict compliance with a term or condition
shall not operate as a waiver or estoppel with respect to, any subsequent or
other failure.

     23. Assignment.

     Neither this Agreement nor the Option created hereunder nor any right,
interest or obligation hereunder shall be assigned by either party without the
prior written consent of the other, except that this Agreement shall be binding
upon and inure to the benefit of the parties hereto and their successors and
permitted assigns.

     24. Currency.

     Except as expressly set forth otherwise, all sums of money referred to in
this Agreement are expressed in lawful money of Canada.


<PAGE>
                                      -13-


     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
signed by their respective duly authorized officers as of the date first above
written.

                         SHIRE PHARMACEUTICALS GROUP PLC

                         By: /s/ Rolf Stahel
                             ---------------------------------------------------
                         Name:   Rolf Stahel
                         Title:  Chief Executive Officer


                         BIOCHEM PHARMA INC.


                         By: /s/ Francesco Bellini
                             ---------------------------------------------------
                         Name:   Francesco Bellini
                         Title:  Chairman and Chief Executive Officer



                         By: /s/ Francois Lagault
                             ---------------------------------------------------
                         Name:   Francois Legault
                         Title:  Executive Vice-President
                                 Corporate Development and Investments