Document:

<PAGE>

                                                                   Exhibit 10.24

================================================================================

                            STOCK PURCHASE AGREEMENT

                                 By and Between

                               NOVARTIS PHARMA AG

                                       AND

                         REGENERON PHARMACEUTICALS, INC.

                           Dated as of March 28, 2003

================================================================================

<PAGE>

                            STOCK PURCHASE AGREEMENT

                  THIS STOCK PURCHASE AGREEMENT ("Agreement"), dated as of March
28, 2003, by and between NOVARTIS PHARMA AG (the "Investor"), a corporation
organized under the laws of Switzerland, with its principal place of business at
Lichtstrasse 35, 4056 Basel, Switzerland, and REGENERON PHARMACEUTICALS, INC.
(the "Company"), a corporation organized under the laws of New York with its
principal place of business at 777 Old Saw Mill Road, Tarrytown, New York,
U.S.A.

                  WHEREAS, concurrently with the execution of this Agreement,
the Investor and the Company have entered into a Collaboration, License and
Option Agreement (the "Collaboration Agreement") and a Registration Rights
Agreement (the "Registration Rights Agreement, and together with the
Collaboration Agreement, the "Transaction Agreements"); and

                  WHEREAS, it is contemplated by the Collaboration Agreement
that the Investor purchases, and the Company issues and sells to the Investor,
shares of common stock of the Company pursuant to the terms and conditions of
this Agreement.

                  NOW, THEREFORE, in consideration of the following mutual
promises and obligations, and for good and valuable consideration the adequacy
and sufficiency of which are hereby acknowledged, the Parties agree as follows:

                                    ARTICLE I

                                   DEFINITIONS

                  Section 1.1       Defined Terms. When used in this Agreement,
the following terms shall have the respective meanings specified therefor below:

                  "Adjustment Period Termination Date" shall mean the thirtieth
trading day immediately succeeding the date hereof.

                  "Business Day" shall mean any day other than a Saturday or
Sunday or a day on which banks located in New York, New York or Basel,
Switzerland are authorized or required by law to close.

                  "Draft Form 10-K" shall mean the draft of the Company's Form
10-K, dated March 4, 2003, for the year ended December 31, 2002, provided to the
Investor by the Company as amended by the substitution of page 14 thereof by a
document delivered to the Investor on March 26, 2003.

                  "Governmental Authority" shall mean any federal, state,
municipal, local, provincial, regional governmental authority in the United
States or other political subdivision thereof and any Person exercising
executive, legislative, judicial regulatory or administrative functions of or
pertaining to government.

<PAGE>

                  "Material Adverse Effect" shall mean any events, occurrences
or circumstances which give rise to or would reasonably be expected to give rise
to, individually or in the aggregate, a material adverse effect on (i) the
business, properties, financial condition or results of operations of the
Company, or (ii) the ability of the Company to comply with its obligations under
the Transaction Agreements.

                  "Per Share Price" shall mean the average closing price per
share of the Company's common stock as quoted in the Wall Street Journal on each
trading day during the period commencing on the eleventh trading day immediately
succeeding the date hereof and ending on (and including) the Adjustment Period
Termination Date.

                  "Person" shall mean and include an individual, a partnership,
a joint venture, a corporation, a limited liability company, a limited liability
partnership, a trust, an incorporated organization and a Governmental Authority.

                  Section 1.2       Additional Defined Terms. In addition to the
terms defined in Section 1.1, the following terms shall have the respective
meanings assigned thereto in the sections indicated below:

<TABLE>
<CAPTION>
         Defined Term              Section             Defined Term             Section
         ------------              -------             ------------             -------
<S>                              <C>           <C>                             <C>
Agreement                        Preamble      Indemnified Parties             6.2
ANDA                             3.16(a)       Indemnifying Party              6.2
Axokine Press Release            6.13(b)       Intellectual Property           3.14(a)(i)
BLA                              3.16(a)       IND                             3.16(a)
Closing                          2.2           Investor                        Preamble
Closing Date Stock               2.1           NDA                             3.16(a)
Collaboration Agreement          Preamble      Organizational Documents        3.1
Company                          Preamble      Purchase Price                  2.1
Company Intellectual Property    3.14(a)(ii)   Purchased Stock                 2.4(a)
Company SEC Documents            3.11          Registration Rights Agreement   Preamble
FDA                              3.16(b)       Securities Act                  3.2(b)
GCP                              3.16(b)       Severed Clause                  6.12
GLP                              3.16(c)       Transaction Agreements          Preamble
</TABLE>

                  Section 1.3       Construction. In this Agreement, unless the
context otherwise requires:

                  (a)      any reference in this Agreement to "writing" or
comparable expressions includes a reference to facsimile transmission or
comparable means of communication;

                  (b)      words expressed in the singular number shall include
the plural and vice versa, words expressed in the masculine shall include the
feminine and neuter gender and vice versa;

                  (c)      references to Articles and Sections are references to
articles and sections of this Agreement;

<PAGE>

                  (d)      reference to "day" or "days" are to calendar days;

                  (e)      this "Agreement" or any other agreement or document
shall be construed as a reference to this Agreement or, as the case may be, such
other agreement or document as the same may have been, or may from time to time
be, amended, varied, novated or supplemented; and

                  (f)      "include," "includes," and "including" are deemed to
be followed by "without limitation" whether or not they are in fact followed by
such words or words of similar import.

                  Section 1.4       Knowledge. Where any representation or
warranty contained in this Agreement is expressly qualified by reference to the
knowledge of the Company, the Company confirms that it has made due and diligent
inquiry as to the matters that are the subject of such representations and
warranty.

                                   ARTICLE II

                        PURCHASE AND SALE OF COMMON STOCK

                  Section 2.1       Issuance of Common Stock. Subject to the
terms and conditions hereof, on the date hereof, the Company agrees to issue and
sell to the Investor, and the Investor agrees to purchase, 2,400,000 shares of
its common stock (the "Closing Date Stock") for an aggregate purchase price of
$48,000,000 (the "Purchase Price"), such number of shares of its common stock to
be adjusted pursuant to Section 2.4

                  Section 2.2       Closing. The purchase and sale of the
Purchased Stock (the "Closing") shall occur on the date hereof at the Company's
offices at 777 Old Saw Mill Road, Tarrytown, New York.

                  Section 2.3       Delivery. The Company shall deliver to the
Investor a stock certificate, registered in the Investor's name, representing
the Purchased Stock, against payment of the Purchase Price by certified or
cashier's check payable to the Company, or by wire transfer of same day funds to
the Company's bank account as follows:

                  Beneficiary Name:              [*  *  *  *]
                  Beneficiary Address:           [*  *  *  *]

                  Account Number:                [*  *  *  *]
                  Bank Name:                     [*  *  *  *]
                  Bank Address:                  [*  *  *  *]

                  Bank Clearing Number:          [*  *  *  *]

                  Section 2.4       Determination of Purchased Stock.

<PAGE>

                  (a)      In the event that the number of shares of common
stock of the Company which is equal to the nearest whole number that is obtained
by dividing $48,000,000 by the Per Share Price is (x) less than the number of
shares of Closing Date Stock, the Investor shall promptly, but in no event later
than the thirty-fifth trading day immediately succeeding the date hereof,
deliver to the Company an amount of shares of common stock of the Company that
is equal to such deficiency, or (y) greater than the number of shares of Closing
Date Stock, the Company shall promptly, but in no event later than the
thirty-fifth trading day immediately succeeding the date hereof, issue and
deliver to the Investor, an amount of shares of common stock of the Company that
is equal to such excess, provided, however that the aggregate amount of the
Company's common stock issued to the Investor pursuant to Section 2.1 and this
subsection (y) shall in no event exceed 19.9% of the issued and outstanding
common stock of the Company as of the date hereof. The Closing Date Stock, as
adjusted pursuant to this Section 2.4, is referred to herein as the "Purchased
Stock").

                  (b)      For the purposes of determining the number of shares
of Purchased Stock required to be delivered pursuant to Section 2.4(a),
adjustment shall be made in the event of any stock split, stock dividend,
reverse stock split, recapitalization or the like that occurs between the
Closing and the Adjustment Period Termination Date.

                                  ARTICLE III

                  REPRESENTATIONS AND WARRANTIES OF THE COMPANY

                  The Company hereby represents and warrants to the Investor as
follows:

                  Section 3.1       Organization, Good Standing and
Qualification. The Company is a corporation duly organized, validly existing and
in good standing under the laws of the State of New York. The Company has all
requisite corporate power and corporate authority to own and operate its
properties and assets, to carry on its business as now conducted, to enter into
the Transaction Agreements, to issue and sell the Purchased Stock and to carry
out the other transactions contemplated under the Transaction Agreements. The
Company is qualified to transact business and is in good standing in each
jurisdiction in which the character of the properties owned, leased or operated
by the Company or the nature of the business conducted by the Company makes such
qualification necessary, except where the failure to be so qualified would not
have a Material Adverse Effect. The Company has delivered to the Investor true,
correct and complete copies of the Company's Restated Certificate of
Incorporation and the Company's By-laws (together, the "Organizational
Documents") as in effect on the date hereof.

                  Section 3.2       Capitalization and Voting Rights.

                  (a)      The authorized capital of the Company as of March 26,
2003 consists of: (i) 160,000,000 shares of common stock, par value $0.001 per
share, of which (x) 42,021,013 shares are issued and outstanding, (y) 2,486,181
shares are reserved for issuance upon conversion of the class A common stock,
each share of class A common stock being convertible into one share of common
stock, and (z) 11,401,366 shares are reserved for issuance pursuant to the
Company's 1990 Long-Term Incentive Plan and 2000 Long-Term Incentive Plan, (ii)
40,000,000 shares of class A common stock, par value $0.001 per share, of which
2,486,181

<PAGE>

shares are issued and outstanding, and (iii) 30,000,000 shares of preferred
stock, par value $0.01 per share, of which no shares are issued and outstanding.
All of the issued and outstanding shares of common stock and class A common
stock have been duly authorized, and all of the issued and outstanding shares of
common stock and class A common stock have been validly issued, are fully paid
and non-assessable, and were issued in compliance with all applicable federal
and state securities laws.

                  (b)      Except as set forth in the Company SEC Documents
filed prior to the date of this Agreement or in the Draft Form 10-K, or as
provided in the Transaction Agreements, there are not, nor upon the consummation
of the transactions contemplated hereby, shall there be: (i) any outstanding
options, warrants, rights (including conversion or preemptive rights) or
agreements pursuant to which the Company is or may become obligated to issue,
sell or repurchase any shares of its capital stock or any other securities of
the Company; (ii) any restrictions on the transfer of capital stock of the
Company imposed by the Organizational Documents, or any agreement to which the
Company is a party, any order of any court or any Governmental Authority to
which the Company is subject, or any law other than state and federal securities
laws; and (iii) any registration rights (including piggy-back rights) under the
Securities Act of 1933, as amended (the "Securities Act") with respect to shares
of the Company's capital stock.

                  (c)      Except as set forth in the Company SEC Documents
filed prior to the date of this Agreement or in the Draft Form 10-K, the Company
is not a party to or subject to any agreement or understanding relating to the
voting of shares of capital stock of the Company or the giving of written
consents by a shareholder or director of the Company.

                  (d)      Since December 31, 2002, the Company has only issued
stock options to its or subsidiaries' employees in the ordinary course of
business, consistent with past practice.

                  Section 3.3       Subsidiaries. The Company does not have
any subsidiaries required to be disclosed in Exhibit 21 to the Draft Form 10-K.

                  Section 3.4       Authorization. All corporate action on the
part of the Company, its directors and stockholders necessary for the
authorization, execution and delivery of the Transaction Agreements, the
performance of all obligations of the Company thereunder, including the
authorization, issuance and delivery of the Purchased Stock, has been taken. The
Transaction Agreements have been duly executed and delivered by the Company and
constitute valid and legally binding obligations of the Company, enforceable
against the Company in accordance with their respective terms (except as such
enforceability may be limited by applicable bankruptcy, insolvency,
reorganization, moratorium or other laws of general application relating to or
affecting enforcement of creditors' rights).

                  Section 3.5       No Conflicts. The execution, delivery and
performance of the Transaction Agreements and compliance with the provisions
thereof by the Company, does not and shall not: (a) violate any provision of
law, statute, ordinance, rule or regulation or any ruling, writ, injunction,
order, judgment or decree of any Governmental Authority, (b) conflict with or
result in any breach of any of the terms, conditions or provisions of, or
constitute (whether or not with due notice or lapse of time, or both) a default
(or give rise to any right of termination,

<PAGE>

cancellation or acceleration) or result in the creation of any lien, security
interest, charge or encumbrance upon any of the properties or assets of the
Company pursuant to any agreement, document, instrument, contract,
understanding, arrangement, note, indenture, mortgage, lease or permit to which
the Company is a party, or under which the Company or any of its assets is bound
or affected, or (c) violate or conflict with any of the provisions of the
Organizational Documents; except, in the case of subsections (a) and (b) as
would not have a Material Adverse Effect.

                  Section 3.6       Valid Issuance of Purchased Stock. When
issued, sold and delivered in accordance with the terms hereof for the
consideration expressed herein, the Purchased Stock shall be validly issued and
outstanding, fully paid and nonassessable, free from any encumbrances or
restrictions on transfer, including preemptive rights, rights of first refusal
or other similar rights, other than restrictions on transfer under the
Transaction Agreements and under federal and state securities laws.

                  Section 3.7       Governmental Consents. No consent, approval,
order or authorization of, or registration, qualification, designation,
declaration or filing with, any Governmental Authority is required in connection
with the consummation of the transactions contemplated by the Transaction
Agreements, except for registration or qualification, or taking such action to
secure exemption from such registration or qualification, of the Purchased Stock
under applicable state or federal securities laws, which actions shall be taken,
by and at the expense of the Company, on a timely basis as may be required.

                  Section 3.8       Litigation. Except as set forth in the
Company SEC Documents filed prior to the date of this Agreement or in the Draft
Form 10-K, there is no action, suit, proceeding or investigation pending or
threatened against the Company or which the Company intends to initiate which
questions the validity of the Transaction Agreements or the right of the Company
to enter into them, or to consummate the transactions contemplated thereby, or
which have a Material Adverse Effect, or result in any material change in the
current equity ownership of the Company.

                  Section 3.9       Licenses and Other Rights; Compliance with
Laws. The Company has all franchises, permits, licenses and other rights and
privileges necessary to permit it to own its properties and to conduct its
business as presently conducted and is in compliance thereunder except where the
failure to be in compliance does not have a Material Adverse Effect. The Company
is and has been in compliance with all laws and governmental rules and
regulations applicable to its business, properties and assets, and to the
products and services sold by it, including, without limitation, all such rules,
laws and regulations relating to fair employment practices, occupational safety
and health and public safety, except where the failure to be in compliance does
not have a Material Adverse Effect.

                  Section 3.10      Compliance with Other Instruments; Action.
The Company has neither received written notice nor otherwise has knowledge of
any violation or default of (a) any of the terms, conditions or provisions of
any agreement, document, instrument, contract, understanding, arrangement, note,
indenture, mortgage, lease or permit to which the Company is a party, or under
which the Company or any of its assets is bound or affected, or (b) the

<PAGE>

Organizational Documents; except, in the case of subsection (a) as would not
have a Material Adverse Effect.

                  Section 3.11      Company SEC Documents; Financial Statements.

                  (a)      Since December 31, 2001, the Company has filed all
required reports, schedules, forms, statements and other documents (including
exhibits and all other information incorporated therein) with the SEC ("Company
SEC Documents"). As of their respective dates, each of the Company SEC Documents
complied, and the Draft Form 10-K complies, in all material respects with the
requirements of the Securities Act or the Securities Exchange Act of 1934, as
amended, and the rules and regulations of the SEC promulgated thereunder
applicable to such Company SEC Documents and the Draft Form 10-K, and no Company
SEC Documents when filed contained, and the Draft Form 10-K does not contain,
any untrue statement of a material fact or omitted to state a material fact
required to be stated therein or necessary in order to make the statements
therein, in light of the circumstances under which they were made, not
misleading.

                  (b)      The financial statements of the Company included in
the Draft Form 10-K comply as to form in all material respects with applicable
accounting requirements and the published rules and regulations of the SEC with
respect thereto, have been prepared in accordance with United States generally
accepted accounting principles applied on a consistent basis during the periods
involved (except as may be indicated in the notes thereto) and fairly present
the financial position of the company as of the dates thereof and the results of
its operations and cash flows for the periods then ended.

                  Section 3.12      Liabilities. The Company does not have any
liabilities, whether absolute, accrued, contingent or otherwise, except for
liabilities (i) set forth in the audited balance sheet for the year ended
December 31, 2002 included in the Draft Form 10-K, or specifically disclosed in
the footnotes thereto or (ii) incurred in the ordinary course of business since
December 31, 2002, that do not have a Material Adverse Effect.

                  Section 3.13      Absence of Changes. Since December 31, 2002,
there has not been a Material Adverse Effect.

                  Section 3.14      Intellectual Property.

                  (a)      For purposes of this Agreement, (i) "Intellectual
Property" shall mean any of the following: (u) patents and patent applications;
(v) registered and unregistered trademarks, service marks and other indicia of
origin, pending trademark and service mark registration applications, and
intent-to-use registrations or similar reservations of marks; (w) registered and
unregistered copyrights and applications therefor; (x) internet domain names,
applications and reservations therefor, uniform resource locators and the
corresponding Internet sites; (y) trade secrets and proprietary information not
otherwise listed in (u) through (x) above, including, without limitation,
unpatented inventions, invention disclosures, confidential information,
technical data, customer lists, corporate and business names, trade names, trade
dress, brand names, know-how, formulae, methods (whether or not patentable),
designs, processes, procedures, technology, source codes, object codes, computer
software programs, databases, data

<PAGE>

collections and other proprietary information or material of any type, and all
derivatives, improvements and refinements thereof, howsoever recorded, or
unrecorded; and (6) any good will associated with any of the foregoing; and (ii)
"Company Intellectual Property" shall mean any Intellectual Property or rights
thereto, owned by or licensed to the Company for use in connection with the
business of the Company.

                  (b)      Except as does not have a Material Adverse Effect,
except as set forth in the Company SEC Documents filed prior to the date of this
Agreement or in the Draft Form 10-K, and except with respect to the Trap-1 (as
such term is defined in the Collaboration Agreement):

                           (i)      each item of Company Intellectual Property
which is registered, filed, issued or applied for, has been duly and validly
registered in, filed in or issued by, the official governmental registrars
and/or issuers (or officially recognized issuers) of patents, trademarks,
copyrights or Internet domain names, in their respective jurisdictions of use
and intended use, and each such registration, filing and/or issuance (x) has not
been abandoned, canceled or otherwise compromised, (y) has been maintained
effective by all requisite filings, renewals and payments, and (z) remains in
full force and effect;

                           (ii)     the Company has the exclusive right to file,
prosecute and maintain all applications and registrations with respect to the
Company Intellectual Property;

                           (iii)    the Company owns or is licensed to use the
Company Intellectual Property free and clear of any Liens, other than Permitted
Liens without, with respect to Company-owned Intellectual Property, obligation
to pay any royalty or any other fees with respect thereto; and

                           (iv)     the Company has not received any notice of
any claim, or a threat of any claim, from any third party, and no third party
claims are pending, (i) challenging the right of the Company to use any
Intellectual Property or alleging any violation, infringement, misuse or
misappropriation by the Company of any Intellectual Property or indicating that
the failure to take a license would result in any such claim, or (ii)
challenging the ownership rights of the Company in any Company Intellectual
Property or asserting any opposition, interference, invalidity, termination,
abandonment, unenforceability, or other infirmity of any Company Intellectual
Property.

                  Section 3.15      Environmental Matters.

                  (a)      For purposes of this Agreement:

                           (i)      "Environmental Claim" means any claim,
action, cause of action, investigation or written notice by any person or entity
alleging potential liability (including, without limitation, potential liability
for investigatory costs, cleanup costs, governmental response costs, natural
resources damages, property damages, personal injuries, or penalties) arising
out of, based on or resulting from (a) the presence or Release of any Hazardous
Materials at any location, whether or not owned or operated by the Company, or
(b) circumstances forming the basis of any violation of any Environmental Law.

<PAGE>

                           (ii)     "Environmental Laws" means all federal,
state, local and foreign laws and regulations relating to pollution or
protection of human health or the environment, including without limitation,
laws relating to Releases or threatened Releases of Hazardous Materials or
otherwise relating to the manufacture, processing, distribution, use, treatment,
storage, transport or handling of Hazardous Materials.

                           (iii)    "Hazardous Materials" means all substances
defined as Hazardous Substances, Oils, Pollutants or Contaminants in the Natural
Oil and Hazardous Substances Pollution Contingency Plan, 40 C.F.R. Section
300.5, or defined as such by, or regulated as such under, any Environmental Law.

                           (iv)     "Release" means any release, spill,
emission, discharge, leaking, pumping, injection, deposit, disposal, dispersal,
leaching or migration into the environment (including, without limitation,
ambient air, surface water, groundwater and surface or subsurface strata) or
into or out of any property, including the movement of Hazardous Materials
through or in the air, soil, surface water, groundwater or property.

                  (b)      Except as set forth in the Company SEC Documents and
the Draft Form 10-K:

                           (i)      the Company is in compliance with all
applicable Environmental Laws (which compliance includes, but is not limited to,
the possession by the Company of all permits and other governmental
authorizations required under applicable Environmental Laws, and compliance with
the terms and conditions thereof), except where failure to so comply would not
have a Material Adverse Effect; and

                           (ii)     there is no Environmental Claim pending or
threatened against the Company which would have a Material Adverse Effect

                  Section 3.16      FDA Matters.

                  (a)      No director, officer or, to the Company's knowledge,
employee of the Company directly involved in clinical trials has ever been
convicted of a felony under law for conduct relating to the development, testing
or approval of any drug, biological product or device, or the preparation or
submission of an Investigational New Drug Application ("IND"), a New Drug
Application ("NDA"), an Abbreviated New Drug Application ("ANDA"), or a
Biologics License Application ("BLA").

                  (b)      All clinical trials conducted, supervised or
monitored by or on behalf of the Company have been conducted in compliance with
all applicable federal, state and local laws, regulations, rules and
requirements, including, but not limited to, current Good Clinical Practices
("GCPs") and the requirements of the regulations of the Food and Drug
Administration ("FDA") at, where applicable, 21 C.F.R. Part 312, and 21 C.F.R.
Part 50, and the Company has not been cited for failure to comply with GCPs,
except where any failure to so comply would not have a Material Adverse Effect.

<PAGE>

                  (c)      All nonclinical studies conducted by or on behalf of
the Company are and have been conducted in accordance with current Good
Laboratory Practices ("GLPs") and the requirements of the regulations of the FDA
at, where applicable, in 21 C.F.R. Part 58, and the Company has not been cited
for failure to comply with GLPs, except where the failure to so conduct such
studies or to so comply would not have a Material Adverse Effect.

                  (d)      Neither the Company nor, to the Company's knowledge,
any of its agents or employees directly involved in clinical trials have been
disqualified or debarred by the FDA under 21 U.S.C. Section 335a, nor has the
Company, to its knowledge, used in any capacity the services of any Person who,
at the time that the services were rendered, was debarred by the FDA under 21
U.S.C. Section 335a, except where such disqualification or debarrment would not
have a Material Adverse Effect.

                  (e)      The Company is in compliance with the applicable
provisions, if any, of the Clinical Laboratories Improvement Act of 1967, as
amended, except where any failure to so comply would not have a Material Adverse
Effect.

                  Section 3.17      Offering. Subject to the accuracy of the
Investor's representations set forth in Section 4.3 and 4.4, the offer, sale and
issuance of the Purchased Stock to be issued in conformity with the terms of
this Agreement constitute transactions which are exempt from the registration
requirements of the Securities Act and from all applicable state registration or
qualification requirements, other than those with which the Company has
complied.

                  Section 3.18      Brokers' or Finders' Fees. No broker,
finder, investment banker or other Person is entitled to any brokerage, finder's
or other fee or commission in connection with the transactions contemplated by
this Agreement.

                                   ARTICLE IV

                 REPRESENTATIONS AND WARRANTIES OF THE INVESTOR

         The Investor hereby represents and warrants as follows:

                  Section 4.1       Organization; Good Standing. The Investor is
a corporation duly organized, validly existing and in good standing under the
laws of Switzerland. The Investor has all requisite corporate power and
corporate authority to enter into the Transaction Agreements, to purchase the
Purchased Stock and to carry out the other transactions contemplated under the
Transaction Documents.

                  Section 4.2       Authorization. All corporate action on the
part of the Investor, and its directors and stockholders necessary for the
authorization, execution and delivery of the Transaction Agreements, the
performance of all obligations of the Investor thereunder, including the
subscription and purchase of the Purchased Stock, has been taken. This Agreement
has been duly executed and delivered by the Investor and constitutes a valid and
legally binding obligation of the Investor, enforceable against the Investor in
accordance with its terms (except as such

<PAGE>

enforceability may be limited by applicable bankruptcy, insolvency,
reorganization, moratorium or other laws of general application relating to or
affecting enforcement of creditors' rights).

                  Section 4.3       Purchase Entirely for Own Account. The
Purchased Stock shall be acquired for investment for the Investor's own account,
not as a nominee or agent, and not with a view to the resale or distribution of
any part thereof, and the Investor has no present intention of selling, granting
any participation, or otherwise distributing the Purchased Stock. The Investor
does not have any contract, undertaking, agreement or arrangement with any
Person to sell, transfer or grant participation to such Person any of the
Purchased Stock.

                  Section 4.4       Investment Experience and Accredited
Investor Status. The Investor either (i) is an "accredited investor" (as defined
in Regulation D under the Securities Act) or (ii) is a "non-U.S. person" (as
defined in Regulation S under the Securities Act) and is not acquiring the
Purchased Stock for the account or benefit of any U.S. Person.

                                   ARTICLE V

                   FURTHER ASSURANCES; SECURITIES LAW MATTERS

                  Section 5.1       Further Assurances. The parties agree to
take such reasonable steps and execute such other and further documents as may
be necessary or appropriate to cause the terms and conditions contained herein
to be carried into effect.

                  Section 5.2       Restricted Securities. The Investor
understands that the Purchased Stock, when issued, shall be restricted
securities under the federal securities laws inasmuch as they are being acquired
from the Company in a transaction not involving a public offering and that under
such laws and applicable regulations such securities may be resold without
registration under the Securities Act only in certain limited circumstances. In
this connection, the Investor represents that it is familiar with Rule 144, as
presently in effect, and understands the resale limitations imposed thereby and
by the Securities Act.

                  Section 5.3       Limitations on Disposition. The Investor
shall not make any disposition of all or any portion of the Purchased Stock,
except to a subsidiary, unless such disposition is in compliance with Article II
of the Registration Rights Agreement and:

                  (a)      there is then in effect a Registration Statement
under the Securities Act covering such proposed disposition and such disposition
is made in accordance with such Registration Statement;

                  (b)      the disposition is made pursuant to Rule 144 or
similar provisions of federal securities laws as in effect from time to time; or

                  (c)      (i) the Investor has notified the Company of the
proposed disposition, and (ii) if requested by the Company, the Investor shall
have furnished the Company with an opinion of counsel (which counsel shall be
reasonably satisfactory to the Company) that such disposition will not require
registration of such shares of the Purchased Stock under the Securities Act. The
Company agrees and acknowledges that for the purpose of any opinion required
pursuant to this

<PAGE>

Section 5.3(c), White & Case LLP shall be considered counsel reasonably
satisfactory to the Company without any further action or request on the part of
the Investor.

                  Section 5.4       Legends. It is understood that the
certificates representing the Purchased Stock shall bear the following legends:

                  (a)      "These securities have not been registered under the
Securities Act of 1933. They may not be sold, offered for sale, pledged or
hypothecated in the absence of a registration statement in effect with respect
to the securities under the Securities Act or an opinion of counsel (which
counsel shall be reasonably satisfactory to the Company) that such registration
is not required or unless sold pursuant to Rule 144 of the Securities Act"; and

                  (b)      any legend required by applicable state securities
laws.

                                   ARTICLE VI

                                  MISCELLANEOUS

                  Section 6.1       Survival of Warranties.

                  (a)      Except as set forth in subsection (b) below, the
respective representations and warranties of the Company and the Investor
contained in this Agreement shall survive the Closing until the thirtieth (30th)
day after the expiration of the applicable statute of limitations (after giving
effect to any waivers and extensions thereto) without regard to any
investigation made by any of the parties hereto

                  (b)      The representations and warranties set forth in
Section 3.15 (Environmental Matters) shall survive indefinitely without regard
to any investigation made by any of the parties hereto.

                  Section 6.2       Indemnification. Each party (an
"Indemnifying Party") shall indemnify, defend and hold the other party and the
other party's directors, officers, employees, agents and affiliates
(collectively, the "Indemnified Parties") harmless against any and all
liabilities, loss, cost or damage, together with all reasonable costs and
expenses related thereto (including legal and accounting fees and expenses),
arising from, relating to, or connected with the untruth or inaccuracy of any
representations or warranties (which untruth or inaccuracy shall, in the case of
the representations and warranties set forth in Section 3.15, be determined
without regard to any reference to "material" "in all material respects,"
"Material Adverse Effect" or other materiality qualifier) as of the date hereof,
or any breach of any covenants of the Indemnifying Party contained herein. The
foregoing indemnification shall survive the termination of this Agreement for
any reason.

                  Section 6.3       Remedies. In case any one or more of the
covenants or agreements set forth in this Agreement shall have been breached by
any party hereto, the party or parties entitled to the benefit of such covenants
or agreements may proceed to protect and enforce their rights either by suit in
equity or action at law, including, but not limited to, an action for damages

<PAGE>

as a result of any such breach or an action for specific performance of any such
covenant or agreement contained in this Agreement. The rights, powers and
remedies of the parties under this Agreement are cumulative and not exclusive of
any other right, power or remedy which such parties may have under any other
agreement or law. No single or partial assertion or exercise of any right, power
or remedy of a party hereunder shall preclude any other or further assertion or
exercise thereof.

                  Section 6.4       Successors and Assigns. Except as otherwise
expressly provided herein, the terms and conditions of this Agreement shall
inure to the benefit of and be binding upon the respective successors and
assigns of the parties. This Agreement and the rights and duties of the Company
set forth herein may not be assigned, in whole or in part, by the Company. The
Investor may assign the right and obligation to purchase the Purchased Stock for
the Purchase Price, and all of its other rights and obligations under the
Transaction Agreements, to any of its subsidiaries, provided that the Investor
shall remain liable for the performance of the obligations such subsidiary
hereunder and thereunder.

                  Section 6.5       Entire Agreement. This Agreement (including
exhibits hereto), together with the Registration Rights Agreement, contains the
complete understanding of the Parties with respect to the subject matter hereof
and thereof and supersedes all prior understandings and writings relating to the
subject matter hereof and thereof. The exhibits to this Agreement are
incorporated into and form an integral part hereof. If an exhibit is a form of
agreement, such agreement, when executed and delivered by the Parties, shall
constitute a document independent of this Agreement.

                  Section 6.6       Governing Law; Submission to Jurisdiction.
This Agreement shall be governed by and construed in accordance with the laws of
the State of New York, without regard to conflict of laws principles. Each of
the parties irrevocably submits to the exclusive jurisdiction of (a) the Supreme
Court of the State of New York, and (b) the United States District Court for the
Southern District of New York, for the purposes of any suit, action or other
proceeding arising out of this Agreement or any transaction contemplated hereby.
Each of the parties agrees to commence any action, suit or proceeding relating
hereto in the United States District Court for the Southern District of New York
or if such suit, action or other proceeding may not be brought in such court for
jurisdictional purposes, in the Supreme Court of the State of New York.

                  Section 6.7       Counterparts. This Agreement may be executed
in counterparts, each of which shall be deemed an original but which together
shall constitute one and the same instrument.

                  Section 6.8       Titles and Subtitles. The titles and
subtitles used in this Agreement are used for convenience only and are not to be
considered in construing or interpreting this Agreement.

                  Section 6.9       Notices. All notices, instructions and other
communications hereunder or in connection herewith shall be in writing, shall be
sent to the address of the relevant party set forth below and shall be (a)
delivered personally, (b) sent by registered or certified mail, return receipt
requested, postage prepaid, (c) sent via a reputable nationwide

<PAGE>

overnight courier service, or (d) sent by facsimile transmission, with a
confirmation copy to be sent by registered or certified mail, return receipt
requested, postage prepaid. Any such notice, instruction or communication shall
be deemed to have been delivered upon receipt if delivered by hand, three (3)
Business Days after it is sent by registered or certified mail, return receipt
requested, postage prepaid, one (1) Business Day after it is sent via a
reputable nationwide overnight courier service, or when transmitted with
electronic confirmation of receipt, if transmitted by facsimile (if such
transmission is on a Business Day; or otherwise, on the next Business Day
following such transmission). Either party may change its address by giving
notice to the other party in the manner provided above.

         To the Company:         Regeneron Pharmaceuticals, Inc.
                                 777 Old Saw Mill Road
                                 Tarrytown, New York 10591
                                 Attention: General Counsel

         With a copy (which      Skadden, Arps, Slate, Meagher & Flom LLP
         shall not constitute    4 Time Square
         notice) to:             New York, NY 10036
                                 Attention: David J. Goldschmidt, Esq.

         To the Investor:        Novartis Pharma AG
                                 Lichtstrasse 35
                                 CH-4002 Basel
                                 Switzerland
                                 Attention: General Counsel

         With a copy to (which:  Novartis Corporation
         shall not constitute    608 Fifth Avenue
         notice) to              New York, New York 10020
                                 Attention: General Counsel and Deputy
                                 General Counsel

                  Section 6.10      Expenses. Each party shall pay its own fees
and expenses with respect to this Agreement. If any action at law or in equity
is necessary to enforce or interpret the terms of this Agreement or the
Articles, the prevailing party shall be entitled to reasonable attorney's fees,
costs and necessary disbursements in addition to any other relief to which such
party may be entitled.

                  Section 6.11      Amendments and Waivers. Any term of this
Agreement may be amended and the observance of any term of this Agreement may be
waived (either generally or in a particular instance and either retroactively or
prospectively), only with the written consent of the Company and the Investor.

                  Section 6.12      Severability. If, under applicable laws, any
provision hereof is invalid or unenforceable, or otherwise directly or
indirectly affects the validity of any other material provision(s) of this
Agreement ("Severed Clause"), then, it is mutually agreed that this Agreement
shall endure except for the Severed Clause. The Parties shall consult and use
their

<PAGE>

reasonable best efforts to agree upon a valid and enforceable provision which
shall be a reasonable substitute for such Severed Clause in light of the intent
of this Agreement.

                  Section 6.13      Confidentiality and Publicity.

                  (a)      Neither the Company nor the Investor shall disclose
to any person (other than its attorneys, accountants, employees, officers, and
directors) the existence or terms of this Agreement or any of the transactions
contemplated hereby without the prior written consent of the other party, except
as may, in the reasonable opinion of such party's counsel, be required by law
(in which event the disclosing party shall first consult with the other party
with respect to such disclosure). If the Company is required to provide a copy
of this Agreement or any related document to any third party, the Company shall
ensure that such document is redacted, to the extent permitted by law, to
eliminate all confidential information. The Investor shall have the right to
review and approve each such document prior to its submission to a third party.
A period of five (5) Business Days shall be provided for such review unless not
permitted by law, in which case the maximum period allowable shall be provided.
The Company and the Investor shall consult and reach agreement with one another
as to the form and substance of any press release or any other public disclosure
of the existence or terms of this Agreement or the transactions contemplated
hereby prior to issuing any such press release or making any such public
disclosure.

                  (b)      The Company shall not later than April 5, 2003, issue
a press release (the "Axokine Press Release") announcing the results of the
initial Phase 3 clinical study for Axokine.

                    [Remainder of page intentionally blank.]

<PAGE>

                  IN WITNESS WHEREOF, the parties have executed and delivered
this Agreement as of the date first above written.

                                    NOVARTIS PHARMA AG

                                    By: /s/ Joseph E. Mamie
                                       -----------------------------------------
                                     Name: Joseph E. Mamie
                                     Title: Head Operational Treasury

                                    By: /s/ Kim Urdahl
                                       -----------------------------------------
                                     Name: Kim Urdahl
                                     Title: Head of Legal, Primary Care

                                    REGENERON PHARMACEUTICALS, INC.

                                    By: /s/ Stuart Kolinski
                                       -----------------------------------------
                                     Name: Stuart Kolinski
                                     Title: Vice President & General Counsel<PAGE>

                                                                   Exhibit 10.25

================================================================================

                          REGISTRATION RIGHTS AGREEMENT

                                 By and Between

                               NOVARTIS PHARMA AG

                                       AND

                         REGENERON PHARMACEUTICALS, INC.

                           Dated as of March 28, 2003

================================================================================

<PAGE>

                          REGISTRATION RIGHTS AGREEMENT

                  THIS REGISTRATION RIGHTS AGREEMENT ("Agreement"), dated as of
March 28, 2003, by and between NOVARTIS PHARMA AG (the "Investor"), a
corporation organized under the laws of Switzerland, with its principal place of
business at Lichtstrasse 35, 4056 Basel, Switzerland, and REGENERON
PHARMACEUTICALS, INC. (the "Company"), a corporation organized under the laws of
New York with its principal place of business at 777 Old Saw Mill Road,
Tarrytown, New York, U.S.A.

                                    RECITALS

                  WHEREAS, the Company and the Investor are parties to a Stock
Purchase Agreement dated as of the date hereof (the "Stock Purchase Agreement"),
pursuant to which the Investor purchased shares of the Company's common stock
(the "Purchased Stock").

                  In consideration of the premises and mutual covenants
contained in this Agreement, the parties hereto hereby agree as follows:

                                   ARTICLE I.

                               REGISTRATION RIGHTS

                  Section 1.1       Definitions.

                  "Affiliate" shall mean, with respect to any Person, any other
Person directly or indirectly controlling, controlled by, or under common
control with, such Person; provided that, for the purposes of this definition,
"control" (including, with correlative meanings, the terms "controlled by" and
"under common control with"), as used with respect to any Person, shall mean the
possession, directly or indirectly, of the power to direct or cause the
direction of the management and policies of such Person, whether through the
ownership of voting securities, by contract or otherwise.

                  "Business Day" shall mean any day other than a Saturday or
Sunday or a day on which banks located in New York, New York or Basel,
Switzerland are authorized or required by law to close.

                  "Common Stock" shall mean the common stock of the Company, par
value $0.001 per share.

                  "Form S-3" shall mean such form under the Securities Act as in
effect on the date hereof or any registration form under the Securities Act
subsequently adopted by the SEC which permits inclusion or incorporation of
substantial information by reference to other documents filed by the Company
with the SEC.

                  "Governmental Authority" shall mean any nation or government,
any federal, state, municipal, local, provincial, regional or other political
subdivision thereof and any Person

<PAGE>

exercising executive, legislative, judicial regulatory or administrative
functions of or pertaining to government.

                  "Holder" shall mean any Person owning Registrable Securities
who is a party to this Agreement or an assignee thereof in accordance with
Section 1.11.

                  "Person" shall mean and include an individual, a partnership,
a joint venture, a corporation, a limited liability company, a limited liability
partnership, a trust, an incorporated organization and a Governmental Authority.

                  "Piggy-Back Rights" shall mean the ability of any Person to
request or require the inclusion of securities in a registration statement that
has been filed, or is proposed to be filed, by the Company for the account of
the Investor pursuant to Section 1.4.

                  "register," "registered," and "registration" refer to a
registration effected by preparing and filing a registration statement or
similar document in compliance with the Securities Act, and the declaration or
ordering of effectiveness of such registration statement or document.

                  "Registrable Securities" shall mean (i) the Purchased Stock
and any shares of Common Stock issued in respect thereof as a result of any
stock split, stock dividend, share exchange, merger, consolidation or similar
recapitalization, and (ii) any Common Stock issued as (or issuable upon the
exercise of any warrant, right or other security that is issued as) a dividend
or other distribution with respect to, or in exchange or in replacement of, the
Purchased Stock, excluding in all cases, however, (x) any Registrable Securities
after they have been sold in a transaction in connection with which registration
rights granted hereunder are not assigned, or (y) any Registrable Securities
sold to or through a broker or dealer or underwriter in a public distribution or
a public securities transaction, or (z) Registrable Securities eligible for
resale pursuant to Rule 144(k) under the Securities Act as provided by, and
subject to the other terms of, Section 1.12.

                  "Registration Expenses" shall mean all expenses incurred by
the Company in complying with Sections 1.4 and 1.6 hereof, including, without
limitation, all registration and filing fees, fees and expenses of compliance
with securities or blue sky laws (including reasonable fees and disbursements of
counsel in connection with blue sky qualifications of any Registrable
Securities), expenses of printing certificates for any Registrable Securities in
a form eligible for deposit with the Depository Trust Company, messenger and
delivery expenses, internal expenses (including, without limitation, all
salaries and expenses of its officers and employees performing legal or
accounting duties), and fees and disbursements of counsel for the Company and
its independent certified public accountants (including the expenses of any
management review, cold comfort letters or any special audits required by or
incident to such performance and compliance), Securities Act liability insurance
(if the Company elects to obtain such insurance), the reasonable fees and
expenses of any special experts retained by the Company in connection with such
registration, fees and expenses of other Persons retained by the Company, and,
in the case of each of the second (2nd) and fourth (4th) Demand Requests, the
reasonable fees and expenses of one (1) counsel for the Holders of Registrable
Securities to be

                                       2

<PAGE>

included in the relevant registration, selected by the Holders of a majority of
the Registrable Securities to be included in such registration.

                  "Securities Act" shall mean the Security Act of 1933, as
amended from time to time, or any successor statute thereto.

                  "Securities Exchange Act" shall mean the Security Exchange Act
of 1934, as amended from time to time, or any successor thereto.

                  "Selling Expenses" shall mean all underwriting discounts and
selling commissions applicable to the sale of Registrable Securities pursuant to
this Agreement.

                  "SEC" shall mean the U.S. Securities and Exchange Commission.

                  "Shares of Then Outstanding Capital Stock" shall mean, at any
time, the issued and outstanding shares of the Common Stock and Class A Stock of
the Company at such time, as well as all capital stock issued and outstanding as
a result of any stock split, stock dividend, or reclassification of Common Stock
or Class A Stock distributable, on a pro rata basis, to all holders of Common
Stock or Class A Stock.

                  Section 1.2       Additional Defined Terms. In addition to the
terms defined in Section 1.1, the following terms shall have the respective
meanings assigned thereto in the sections indicated below:

<TABLE>
<CAPTION>
    Defined Term       Section             Defined Term            Section
    ------------       -------             ------------            -------
<S>                    <C>        <C>                              <C>
Acquisition Proposal   2.1(c)     Offered Registrable Securities    2.5
Agreement              Preamble   Permitted Transfer                2.4
Authorization Date     2.5        Required Registration             1.4(a)
Demand Request         1.4(a)     Sale Notice                       2.5
Initiating Holders     1.4(b)     Severed Clause                    3.10
Lock-Up Period         2.4        Third Party Piggy-Back Request    1.4(c)
Notice Period          2.5        Transfer                          2.4
Offeror                2.1(c)     Violation                         1.9(a)
</TABLE>

                  Section 1.3       Construction. In this Agreement, unless the
context otherwise requires:

                  (a)      any reference in this Agreement to "writing" or
comparable expressions includes a reference to facsimile transmission or
comparable means of communication;

                  (b)      words expressed in the singular number shall include
the plural and vice versa, words expressed in the masculine shall include the
feminine and neuter gender and vice versa;

                  (c)      references to Articles, Sections and Schedules are
references to articles, sections and schedules of this Agreement;

                                       3

<PAGE>

                  (d)      reference to "day" or "days" are to calendar days;

                  (e)      this "Agreement" or any other agreement or document
shall be construed as a reference to this Agreement or, as the case may be, such
other agreement or document as the same may have been, or may from time to time
be, amended, varied, novated or supplemented; and

                  (f)      "include," "includes," and "including" are deemed to
be followed by "without limitation" whether or not they are in fact followed by
such words or words of similar import.

                  Section 1.4 Required Registration. If, at any time after the
second anniversary of the date of this Agreement, the Company receives from any
Holder or Holders a written request or requests (each, a "Demand Request") that
the Company effect a registration (a "Required Registration") under the
Securities Act and any related qualification or compliance with respect to
shares of Registrable Securities, the Company shall:

                  (i)      promptly give written notice of the proposed
registration, and any related qualification or compliance, to any Holders which
did not make such Demand Request; and

                  (ii)     as soon as practicable, effect all such
qualifications and compliance as may be so requested and as would permit or
facilitate the sale and distribution of all or such portion of such Holder's or
Holders' Registrable Securities as are specified in such request, together with
all or such portion of the Registrable Securities of any other Holder or Holders
joining in such request as are specified in a written request given by such
other Holder or Holders within fifteen (15) days after receipt of such written
notice from the Company; provided, however, that the Company shall not be
obligated to effect any such registration, qualification or compliance, pursuant
to this Section 1.4:

                  (1)      if the Company has already completed four (4)
Required Registrations;

                  (2)      if the market value of the Registrable Securities
proposed to be included in the registration, based on the average closing price
during the ten (10) consecutive trading days period prior to the making of the
Demand Request, is less than $10,000,000;

                  (3)      if the Company shall furnish to the Holders a
certificate signed by the President and Chief Executive Officer of the Company
stating that (i) within sixty (60) days of receipt of the request of the Holder
or Holders under this Section 1.4 the Company shall file a registration
statement for the public offering of securities for the account of the Company
(other than a registration of securities (a) issuable pursuant to an employee
stock option, stock purchase or similar plan, (b) issuable pursuant to a merger,
exchange offer or a transaction of the type specified in Rule 145(a) under the
Securities Act, or (c) in which the only securities being registered are
securities issuable upon conversion of debt securities which are also being
registered), or (ii) the Company is engaged in a material transaction or has an
undisclosed material corporate development, in either case, which would be
required to be disclosed in the registration statement, and in the good faith
judgment of the Board of Directors of the Company, such disclosure would be
seriously detrimental to the Company and its shareholders at such time

                                       4

<PAGE>

(in which case, the Company shall disclose the matter as promptly as reasonably
practicable and thereafter file the registration statement and each Holder
agrees not to disclose any information about such material transaction to third
parties until such disclosure has occurred or such information has entered the
public domain other than through breach of this provision by such Holder),
provided that the Company shall have the right to only defer the filing of the
registration statement pursuant to this subsection, such deferral to be for a
period of not more than ninety (90) days after receipt of a Demand Request and
provided further, that the Company may only defer the filing of a registration
pursuant to this subsection once in any one (1) year period; or

                  (4)      if the Company has, within the six (6) month period
preceding the date of the Demand Request, already effected one (1) Required
Registration for the Holders pursuant to this Section 1.4.

                  (b)      If the Holders initiating the registration request
hereunder (the "Initiating Holders") intend to distribute the Registrable
Securities covered by their request by means of an underwriting, they shall so
advise the Company as a part of their Demand Request made pursuant to Section
1.4(a) and the Company shall include such information in the written notice
referred to in Section 1.4(a)(i). The underwriter shall be selected by a
majority in interest of the Initiating Holders and shall be acceptable to the
Company. In such event, the right of any Holder to include its Registrable
Securities in such registration shall be conditioned upon such Holder's
participation in such underwriting and the inclusion of such Holder's
Registrable Securities in the underwriting (unless otherwise mutually agreed by
a majority in interest of the Initiating Holders and such Holder) to the extent
provided herein. All Holders proposing to distribute their securities through
such underwriting shall (together with the Company as provided in Section
1.6(h)) enter into an underwriting agreement in customary form with the
underwriter or underwriters selected for such underwriting. Notwithstanding any
other provision of this Section 1.4, if the managing underwriter determines in
good faith that marketing factors require a limitation of the number of shares
to be underwritten, then the Company shall so advise all Holders of Registrable
Securities which would otherwise be underwritten pursuant hereto, and the number
of shares of Registrable Securities that may be included in the underwriting
shall be allocated among all Holders thereof, including the Initiating Holders,
in proportion (as nearly as practicable) to the amount of Registrable Securities
of the Company owned by each Holder; provided, however, that the number of
shares of Registrable Securities to be included in such underwriting shall not
be reduced unless all other securities are first entirely excluded from the
underwriting.

                  (c)      Except as set forth on Schedule 1.4(c), the Company
represents and warrants to the Investor that as of the date of this Agreement,
in the event that any Person is entitled to request (a "Third Party Piggy-Back
Request") the inclusion of securities held by it in any Required Registration
requested pursuant to this Section 1.4, the terms of the agreement pursuant to
which the Company granted such Third Party Piggy-Back Request permit the Company
to exclude such securities from the Demand Registration in their entirety in
accordance with the provisions of Section 1.4(b) if the managing underwriter
determines in good faith that marketing factors require a limitation of the
number of shares to be underwritten.

                                       5

<PAGE>

                  Section 1.5       Piggy-Back Registration. The Company
covenants and agrees that, following the date of this Agreement, it will not
grant any Person any Piggy-Back Rights.

                  Section 1.6       Obligations of the Company. Whenever
required under Section 1.4 to effect the registration of any Registrable
Securities, the Company shall, as expeditiously as reasonably possible:

                  (a)      prepare and file with the SEC a registration
statement with respect to such Registrable Securities sought to be included
therein; provided that, to the extent practicable, at least five (5) Business
Days prior to filing any registration statement or prospectus or any amendments
or supplements thereto, the Company shall furnish to the Holders of the
Registrable Securities covered by such registration statement and their counsel
copies of all such documents proposed to be filed and any such Holder shall have
the opportunity to comment on any information pertaining solely to such Holder
and its plan of distribution that is contained therein and the Company shall
make the corrections reasonably requested by such Holder with respect to such
information prior to filing any such registration statement or amendment;

                  (b)      prepare and file with the SEC such amendments and
post-effective amendments to any registration statement and any prospectus used
in connection therewith as may be necessary to keep such registration statement
effective, and cause the prospectus to be supplemented by any required
prospectus supplement, and as so supplemented to be filed pursuant to Rule 424
under the Securities Act, and to comply with the provisions of the Securities
Act with respect to the disposition of all Registrable Securities covered by
such registration statement for a period of not less than one-hundred twenty
(120) days or, if occurring earlier, the date on which the sale of all of the
Registrable Securities included in such registration statement shall be
completed;

                  (c)      furnish to the Holders such numbers of copies of such
registration statement, each amendment and supplement thereto, the prospectus
included in such registration statement (including each preliminary prospectus),
in conformity with the requirements of the Securities Act, and such other
documents as they may reasonably request in order to facilitate the disposition
of Registrable Securities owned by them;

                  (d)      notify the Holders, promptly after the Company shall
receive notice thereof, of the time when a registration statement becomes
effective or when any amendment or supplement or any prospectus forming a part
of the registration statement has been filed;

                  (e)      notify the Holders promptly of any request by the SEC
for the amending or supplementing of any registration statement or prospectus or
for additional information and promptly deliver to a Holder copies of any
comments received from the SEC to the extent such comments pertain to such
Holder;

                  (f)      notify the Holders promptly of any stop order
suspending the effectiveness of any registration statement or prospectus or the
initiation of any proceedings for that purpose, and use its best efforts to
obtain the withdrawal of any such order or the termination of such proceedings;

                                       6

<PAGE>

                  (g)      use its best efforts to register and qualify the
securities covered by such registration statement under such other securities or
"blue sky" laws of such jurisdictions as shall be reasonably requested by the
Holders and use its best efforts to keep each such registration or qualification
effective, including through new filings, or amendments or renewals, during the
period such registration statement is required to be kept effective; and do any
and all other acts or things necessary or advisable to enable the disposition of
the Registrable Securities in all such jurisdictions reasonably requested to be
covered by such registration, provided that the Company shall not be required in
connection therewith or as a condition thereto to qualify to do business or to
file a general consent to service of process in any such states or
jurisdictions;

                  (h)      in the event of any underwritten public offering,
enter into and perform its obligations under an underwriting agreement, in usual
and customary form, with the managing underwriter of such offering;

                  (i)      use its reasonable efforts to obtain: (A) at the time
of effectiveness of each registration statement, a "cold comfort letter" from
the Company's independent certified public accountants covering such matters of
the type customarily covered by "cold comfort letters" as the Holders of
Registrable Securities covered by such registration statement and the
underwriters reasonably request; and (B) at the time of any underwritten sale
pursuant to the registration statement, a "bring-down comfort letter," dated as
of the date of such sale, from the Company's independent certified public
accountants covering such matters of the type customarily covered by "bring-down
comfort letters" as the Holders of Registrable Securities covered by such
registration statement and the underwriters reasonably request;

                  (j)      promptly notify each Holder of Registrable Securities
covered by such registration statement at any time when a prospectus relating
thereto is required to be delivered under the Securities Act of the happening of
any event as a result of which the prospectus included in such registration
statement or any offering memorandum or other offering document includes an
untrue statement of a material fact or omits to state any material fact required
to be stated therein or necessary to make the statements therein not misleading
in the light of the circumstances then existing, and prepare a supplement or
amendment to such prospectus so that, as thereafter delivered to the purchasers
of such shares, such prospectus will not contain an untrue statement or material
fact or omit to state any fact necessary to make the statements therein not
misleading;

                  (k)      permit any Holder, which Holder in its judgment might
be deemed to be an underwriter or a controlling Person of the Company, to
participate in the preparation of such registration statement and to require the
insertion therein of material, furnished to the Company in writing, which in the
reasonable judgment of such Holder and its counsel should be included; and

                  (l)      use its reasonable efforts to obtain an opinion or
opinions addressed to the underwriter or underwriters of any underwritten
offering of Registrable Securities, if any, in customary form and scope from
counsel for the Company; and

                  (m)      use its best efforts to cause all such Registrable
Securities to be listed on each exchange on which similar securities issued by
the Company are then listed.

                                       7

<PAGE>

                  Section 1.7       Furnish Information. It shall be a condition
precedent to the obligations of the Company to take any action pursuant to this
Agreement with respect to the Registrable Securities of any selling Holder that
such Holder shall furnish to the Company such information regarding itself, the
Registrable Securities held by it, and the intended method of disposition of
such securities as shall be reasonably necessary to effect the registration of
such Holder's Registrable Securities.

                  Section 1.8       Expenses. Except as specifically provided
herein, all Registration Expenses incurred in connection with any registration,
qualification or compliance pursuant to Section 1.4 or 1.6 hereof shall be borne
by the Company. All Selling Expenses incurred in connection with any
registration hereunder shall be borne by the Holders of Registrable Securities
covered by a registration statement pro rata on the basis of the number of
Registrable Securities registered on their behalf.

                  Section 1.9       Indemnification. In the event any
Registrable Securities are included in a registration statement under this
Agreement:

                  (a)      The Company shall indemnify and hold harmless each
Holder including Registrable Securities in such registration statement, any
underwriter (as defined in the Securities Act) for such Holder and each Person,
if any, who controls such Holder or underwriter within the meaning of the
Securities Act or the Securities Exchange Act, against any and all losses,
claims, damages, or liabilities (joint or several) to which they may become
subject under any securities laws including, without limitation, the Securities
Act, the Securities Exchange Act, or any other statute or common law of the
United States or any other country or political subdivision thereof, or
otherwise, including the amount paid in settlement of any litigation commenced
or threatened (including any amounts paid pursuant to or in settlement of claims
made under the indemnification or contribution provisions of any underwriting or
similar agreement entered into by such Holder in connection with any offering or
sale of securities covered by this Agreement), and shall promptly reimburse
them, as and when incurred, for any legal or other expenses incurred by them in
connection with investigating any claims and defending any actions, insofar as
any such losses, claims, damages, or liabilities (or actions in respect thereof)
arise out of or are based upon any of the following statements, omissions or
violations (collectively, a "Violation"): (i) any untrue statement or alleged
untrue statement of a material fact contained in such registration statement,
including any preliminary prospectus or final prospectus contained therein or
any amendments or supplements thereto, or in any offering memorandum or other
offering document relating to the offering and sale of such securities, (ii) the
omission or alleged omission to state therein a material fact required to be
stated therein, or necessary to make the statements therein not misleading, or
(iii) any violation or alleged violation by the Company of the Securities Act,
the Securities Exchange Act, any state securities law or any rule or regulation
promulgated under the Securities Act, the Securities Exchange Act or any state
Securities Law; or other applicable laws of any jurisdiction relating to any
actual or alleged action or inaction required of the Company in connection with
such offering; provided, however, the Company shall not be liable in any such
case for any such loss, claim, damage, liability or action to the extent that it
arises out of or is based upon a Violation which occurs in reliance upon and in
conformity with written information furnished expressly for use in connection
with such registration by such Holder.

                                       8

<PAGE>

                  (b)      Each Holder including Registrable Securities in a
registration statement shall indemnify and hold harmless the Company, each of
its directors, each of its officers who has signed the registration statement,
each Person, if any, who controls the Company within the meaning of the
Securities Act, any underwriter, any other Holder selling securities in such
registration statement and any controlling Person of any such underwriter or
other Holder, against any losses, claims, damages, or liabilities (joint or
several) to which any of the foregoing Persons may become subject, under
liabilities (or actions in respect thereto) which arise out of or are based upon
any Violation, in each case to the extent (and only to the extent) that such
Violation occurs in reliance upon and in conformity with written information
furnished by such Holder expressly for use in connection with such registration;
and each such Holder shall pay, as incurred, any legal or other expenses
reasonably incurred by any Person intended to be indemnified pursuant to this
Section 1.9(b), in connection with investigating or defending any such loss,
claim, damage, liablity, or action; provided, however, that the indemnity
agreement contained in this Section 1.9(b) shall not apply to amounts paid in
settlement of any such loss, claim, damage, liability or action if such
settlement is effected without consent of the Holder, which consent shall not be
unreasonably withheld; provided, that, in no event shall any indemnity under
this Section 1.9(b) exceed the net proceeds from the offering received by such
Holder.

                  (c)      Promptly after receipt by an indemnified party under
this Section 1.9 of notice of the commencement of any action (including any
governmental action), such indemnified party shall, if a claim in respect
thereof is to be made against any indemnifying party under this Section 1.9,
deliver to the indemnifying party a written notice of the commencement thereof
and the indemnifying party shall have the right to participate in, and, to the
extent the indemnifying party so desires, jointly within any other indemnifying
party similarly noticed, to assume the defense thereof with counsel mutually
satisfactory to the parties; provided, however, that an indemnified party shall
have the right to retain its own counsel, with the fees and expenses to be paid
by the indemnifying party, if representation of such indemnified party by the
counsel retained by the indemnifying party would be inappropriate due to actual
or potential differing interests between such indemnified party and any other
party represented by such counsel in such proceeding. The failure to deliver
written notice to the indemnifying party within a reasonable time of the
commencement of any such action, if prejudicial to its ability to defend such
action, shall relieve such indemnifying party of any liability to the
indemnified party under this Section 1.9, but the omission so to deliver written
notice to the indemnifying party shall not relieve it of any liability that it
may have to any indemnified party otherwise than under this Section 1.9.

                  (d)      In order to provide for just and equitable
contribution to joint liability in any case in which a claim for indemnification
is made pursuant to this Section 1.9 but it is judicially determined (by the
entry of a final judgment or decree by a court of competent jurisdiction and the
expiration or time to appeal or the denial of the last right of appeal) that
such indemnification may not be enforced in such case notwithstanding the fact
that this Section 1.9 provided for indemnification in such case, the Company and
each Holder of Registrable Securities shall contribute to the aggregate losses,
claims, damages or liabilities to which they may be subject (after contribution
from others) in proportion to the relative fault of the Company, on the one
hand, and such Holder, severally, on the other hand; provided, however,

                                       9

<PAGE>

that in any such case, no Person guilty of fraudulent misrepresentation (within
the meaning of Section 11(f) of the Securities Act) shall be entitled to
contribution from any Person who was not guilty of such fraudulent
misrepresentation and; provided, further, that in no event shall any
contribution under this Section 1.9(d) on the part of any Holder exceed the net
proceeds received by such Holder from the sale of Registrable Securities.

                  (e)      The obligations of the Company and the Holders under
this Section 1.9 shall survive the completion of any offering of Registrable
Securities in a registration statement under this Agreement and otherwise.

                  Section 1.10      Reports Under Securities Exchange Act. With
a view to making available to the Holders the benefits of Rule 144 promulgated
under the Securities Act and any other rule or regulation of the SEC that may at
any time permit a Holder to sell securities of the Company to the public without
registration or pursuant to a registration on Form S-3, the Company agrees to:

                  (a)      file with the SEC in a timely manner all reports and
other documents required of the Company under the Securities Act and the
Securities Exchange Act; and

                  (b)      furnish to any Holder, so long as such Holder owns
any Registrable Securities, forthwith upon request (i) a written statement by
the Company that it has complied with the reporting requirements of SEC Rule
144, the Securities Act and the Securities Exchange Act, or that it qualifies as
a registrant whose securities may be resold pursuant to Form S-3 (at any time
after it so qualifies), (ii) a copy of the most recent annual or quarterly
report of the Company and such other reports and documents so filed by the
Company, and (iii) such other information as may be reasonably requested in
availing any Holder of any rule or regulation of the SEC (exclusive of Rule
144A) which permits the selling of any such securities without registration or
pursuant to such form.

                  Section 1.11      Assignment of Registration Rights. The
rights to cause the Company to register any Registrable Securities pursuant to
this Agreement may be assigned (but only with all related obligations) by a
Holder to a transferee or assignee of such Registrable Securities that (i) is a
subsidiary of a Holder, or (ii) acquires not less than all of the shares of
Registrable Securities initially acquired by the Investor on the date of this
Agreement (as adjusted for stock splits, stock dividends, stock combinations and
the like); provided, however, (A) the transferor shall, within ten (10) days
after such transfer, furnish to the Company with written notice of the name and
address of such transferee or assignee and, in the case of a transfer in
accordance with subclause (i) above, details of the Registrable Securities with
respect to which such registration rights are being assigned, (B) such
transferee or assignee, prior to such transfer or assignment, shall agree in
writing to be subject to and bound by all restrictions set forth in this
Agreement including the provisions of Article II, and (C) such transfer or
assignment shall be effective only if immediately following such transfer or
assignment the further disposition of such Registrable Securities by the
transferee or assignee is restricted under the Securities Act and other
applicable securities law.

                                       10

<PAGE>

                  Section 1.12      Rule 144. The Company shall not be required
to include the Registrable Securities of any Holder in a registration statement
filed pursuant to Section 1.4 if the Company delivers to such Holder(s) an
opinion of counsel, in form and substance reasonably acceptable to such
Holder(s), to the effect that the Registrable Securities requested to be
included in such Registration by the Holder may then be sold pursuant to Rule
144(k) of the Securities Act.

                                   ARTICLE II.

                  RESTRICTIONS ON ACQUISITIONS AND DISPOSITIONS

                  Section 2.1       Standstill. Prior to the earlier of (i) the
termination by the Investor of the Collaboration Agreement pursuant to Section
19.5 thereof, and (ii) the fifth anniversary of the date of this Agreement,
without the express written consent of the Company, the Investor and its
Affiliates shall not:

                  (a)      directly or indirectly, acquire beneficial ownership
of Shares of Then Outstanding Capital Stock or any securities convertible into
or exchangeable for Shares of Then Outstanding Capital Stock, or make a tender,
exchange or other offer to acquire Shares of Then Outstanding Capital Stock, if
after giving effect to such acquisition, the Investor would beneficially own (as
defined in Rule 13d-3 under the Securities Exchange Act) more than nineteen and
nine-tenths percent (19.9%) of the Shares of Then Outstanding Capital Stock;
provided, however, that notwithstanding the provisions of this Section 2.1(a),
if the number of shares constituting Shares of Then Outstanding Capital Stock is
reduced or if the aggregate ownership of the Investor is increased as a result
of a recapitalization of the Company, the Investor shall not be required to
dispose of any of its holdings of Shares of Then Outstanding Capital Stock even
though such action resulted in the Investor's ownership exceeding nineteen and
nine-tenths percent (19.9%) of the Shares of Then Outstanding Capital Stock;

                  (b)      directly or indirectly, propose, nominate or support
for election to the Board of Directors any Person whose nomination has not been
approved by a majority of the Board of Directors, or vote or cause to be voted
in favor of any such Person any Shares of Then Outstanding Capital Stock;

                  (c)      directly or indirectly, encourage or support a
tender, exchange or other offer or proposal by any other Person or group (an
"Offeror") the consummation of which would result in a "change of control" of
the Company (an "Acquisition Proposal");

                  (d)      directly or indirectly, solicit proxies or consents
or become a participant in a solicitation (as such terms are defined in
Regulation 14A under the Securities Exchange Act) in opposition to the
recommendation of a majority of the Board of Directors of the Company with
respect to any matter, or seek to advise or influence any person, with respect
to voting of any Shares of Then Outstanding Capital Stock of the Company or any
of its subsidiaries;

                                       11

<PAGE>

                  (e)      deposit any Shares of Then Outstanding Capital Stock
in a voting trust or subject any Shares of Then Outstanding Capital Stock to any
arrangement or agreement with respect to the voting of such Shares of Then
Outstanding Capital Stock; or

                  (f)      instigate, act in concert with or assist any third
party to take any action in clauses (a) through (e) above;

provided that the mere voting of any Shares of Then Outstanding Capital Stock
held by the Investor shall not constitute a violation of any of clauses (a)
through (e) above.

                  Section 2.2       Termination of Standstill. The restrictions
contained in Section 2.1 shall terminate upon the earlier to occur of (i) the
public announcement by an Offeror of an Acquisition Proposal; (ii) the
acquisition by an Offeror (other than Leonard Schleifer) of beneficial ownership
of Shares of Then Outstanding Capital Stock, which, when combined with all other
Shares of Then Outstanding Capital Stock beneficially owned by the Offeror,
represents more than twenty percent (20%) of the voting power represented by all
issued and outstanding Shares of Then Outstanding Capital Stock; (iii) the entry
by the Company into negotiations with any third party or group with respect to a
transaction which, if consummated, would result in a "change of control," (iv)
the issuance by the Company to a third party of Shares of Then Outstanding
Capital Stock, which, when combined with all other Shares of Then Outstanding
Capital Stock beneficially owned by such third party, represents more than seven
percent (7%) of the voting power represented by all issued and outstanding
Shares of Then Outstanding Capital Stock, if the Company does not enter into a
standstill agreement for a time period and upon terms substantially similar to
the provisions of this Section 2; (v) a sale of all or substantially all of the
assets of the Company (other than to a wholly owned subsidiary of the Company);
or (vi) a liquidation or dissolution of the Company.

                  Section 2.3       Change of Control. For purposes this Article
II, a "change of control" shall mean (i) a merger or consolidation to which the
Company is a party and as a result of which the Persons who were stockholders of
the Company immediately prior to the effective date of such merger or
consolidation beneficially own (as defined in Rule 13d-3 under the Securities
Exchange Act) less than fifty percent (50%) of the voting stock of the surviving
parent entity outstanding immediately following the effectiveness of such merger
or consolidation; (ii) a sale of all or substantially all of the Company's
assets (other than to a wholly-owned subsidiary of the Company); or (iii) a
liquidation or dissolution of the Company.

                  Section 2.4       Lock-Up. Prior to the second anniversary of
the date of this Agreement (the "Lock-up Period"), without the approval of a
majority of the Board of Directors of the Company, the Investor shall not sell
or otherwise transfer, directly or indirectly, Registrable Securities (each, a
"Transfer"), provided, however that the foregoing shall not prohibit the
Investor from transferring all or part of the Purchased Stock to a subsidiary
which agrees to be bound by the terms hereof, and provided, further, that,
subject to compliance with the terms of Section 2.5, during the Lock-up Period
the Company may Transfer Registrable Securities in a transaction that is exempt
from the registration requirements of the Securities Act (other than pursuant to
Rule 144 under the Securities Act) (a "Permitted Transfer") subject to the terms
of Section 2.5.

                                       12

<PAGE>

                  Section 2.5       Permitted Transfer; Right of First Offer.

                  (a)      Prior to a Permitted Transfer to any Person of
Registrable Securities by the Investor, the Investor shall give written notice
(the "Sale Notice") to the Company. The Sale Notice shall (i) disclose the price
and terms upon which the Investor is willing to sell to the Company some or all
of the Registrable Securities held by it (the "Offered Registrable Securities"),
and (ii) confirm that the offer to purchase such Registrable Securities is
irrevocable for a period of at least ten (10) days (the "Notice Period"). The
Investor shall not consummate any Transfer until the earlier of (x) the
conclusion of the Notice Period and (y) the date on which the Company notifies
the Investor that it does not wish to purchase all (but not less than all) of
the Offered Registrable Securities (such earlier date, the "Authorization
Date").

                  (b)      The Company may elect to purchase all (but not less
than all) of the Offered Registrable Securities upon the same terms and
conditions as those set forth in the Sale Notice by delivering a written notice
of such election to the Investor within ten (10) days after the Sale Notice has
been delivered to the Company. If the Company has not elected to purchase all of
the Offered Registrable Securities within ten (10) days after the Sale Notice
has been delivered to Company, the Investor may, during the sixty (60) day
period immediately following the Authorization Date, Transfer all such Offered
Registrable Securities specified in the Sale Notice at a price and on terms no
more favorable than those specified in the Sale Notice. Any Offered Registrable
Securities not Transferred during such sixty (60) day period shall be subject to
the provisions of this Section 2.5 upon a subsequent proposed Transfer prior to
the end of the Lock-up Period.

                  (c)      If the Company has agreed to purchase all of the
Offered Registrable Securities set forth in the Sale Notice pursuant to Section
2.5(b), the closing of such purchase shall occur within ten (10) Business Days
from the date the Company has notified the Investor of its intention to purchase
all of such Offered Registrable Securities.

                  Section 2.6       Legend.

                  (a)      Prior to the termination of the Lock-Up Period, each
certificate representing Registrable Securities shall bear the following legend:

                  PURSUANT TO THE TERMS AND CONDITIONS OF A REGISTRATION RIGHTS
                  AGREEMENT DATED MARCH 27, 2003, BY AND BETWEEN THE COMPANY AND
                  NOVARTIS PHARMA A.G., THE SECURITIES REPRESENTED BY THIS
                  CERTIFICATE MAY NOT BE SOLD OR OTHERWISE TRANSFERRED PRIOR TO
                  MARCH 28, 2005.

                  (b)      Following the termination of the Lock-Up Period, the
holder of any stock certificate bearing such legend may submit such certificate
to the Company in exchange for a share certificate duly issued by the Company
which shall be identical in all material respects, except that it shall not bear
the foregoing legend.

                                       13

<PAGE>

                  Section 2.7       Injunctive Relief. It is hereby agreed and
acknowledged that it will be impossible to measure in money the damages that
would be suffered by the Company if the Investor fails to comply with the terms
of this Article II and that in the event of any such failure, the Company will
be irreparably damaged and will not have an adequate remedy at law. Each party
agrees (i) that in any action for equitable remedies arising from a breach of
this Article II, the Company will not be required to prove the inadequacy or
insufficiency of money damages as a remedy and (ii) to waive any requirement for
a bond in connection with any such injunctive or equitable relief or action
therefor.

                                  ARTICLE III.

                                  MISCELLANEOUS

                  Section 3.1       Amendment; Waiver. Any term of this
Agreement may be amended or waived only with the written consent of the Company
and the Holders of at least two-thirds (2/3) of the Registrable Securities then
outstanding; provided, however, that Section 2 may be amended or waived solely
with the written consent of the Company and the Investor.

                  Section 3.2       Remedies. In case any one or more of the
covenants or agreements set forth in this Agreement shall have been breached by
any party hereto, the party or parties entitled to the benefit of such covenants
or agreements may proceed to protect and enforce their rights either by suit in
equity or action at law, including, but not limited to, an action for damages as
a result of any such breach or an action for specific performance of any such
covenant or agreement contained in this Agreement. The rights, powers and
remedies of the parties under this Agreement are cumulative and not exclusive of
any other right, power or remedy which such parties may have under any other
agreement or law. No single or partial assertion or exercise of any right, power
or remedy of a party hereunder shall preclude any other or further assertion or
exercise thereof.

                  Section 3.3       Successors and Assigns. Except as otherwise
expressly provided herein, the terms and conditions of this Agreement shall
inure to the benefit of and be binding upon the respective successors and
assigns of the parties. This Agreement and the rights and duties of the Company
set forth herein may not be assigned, in whole or in part, by the Company.

                  Section 3.4       Entire Agreement. This Agreement, together
with the Stock Purchase Agreement (including exhibits thereto), contains the
complete understanding of the Parties with respect to the subject matter hereof
and supersedes all prior understandings and writings relating to the subject
matter hereof and thereof.

                  Section 3.5       Governing Law; Consent to Jurisdiction. This
Agreement shall be governed by and construed in accordance with the laws of the
State of New York, without regard to conflict of laws principles. Each of the
parties irrevocably submits to the exclusive jurisdiction of (a) the Supreme
Court of the State of New York, and (b) the United States District Court for the
Southern District of New York, for the purposes of any suit, action or other
proceeding arising out of this Agreement or any transaction contemplated hereby.
Each of the

                                       14

<PAGE>

parties agrees to commence any action, suit or proceeding relating hereto in the
United States District Court for the Southern District of New York or if such
suit, action or other proceeding may not be brought in such court for
jurisdictional purposes, in the Supreme Court of the State of New York.

                  Section 3.6       Counterparts. This Agreement may be executed
in counterparts, each of which shall be deemed an original but which together
shall constitute one and the same instrument.

                  Section 3.7       Titles and Subtitles. The titles and
subtitles used in this Agreement are used for convenience only and are not to be
considered in construing or interpreting this Agreement.

                  Section 3.8       Nouns and Pronouns. Whenever the context may
require, any pronouns used herein shall include the corresponding masculine,
feminine or neuter forms, and the singular form of names and pronouns shall
include the plural and vice-versa.

                  Section 3.9       Notices. All notices, instructions and other
communications hereunder or in connection herewith shall be in writing, shall be
sent to the address of the Holder set forth below or as provided to the Company
upon any Person becoming a Holder, and shall be (a) delivered personally, (b)
sent by registered or certified mail, return receipt requested, postage prepaid,
(c) sent via a reputable nationwide overnight courier service, or (d) sent by
facsimile transmission, with a confirmation copy to be sent by registered or
certified mail, return receipt requested, postage prepaid. Any such notice,
instruction or communication shall be deemed to have been delivered upon receipt
if delivered by hand, three (3) Business Days after it is sent by registered or
certified mail, return receipt requested, postage prepaid, one (1) Business Day
after it is sent via a reputable nationwide overnight courier service, or when
transmitted with electronic confirmation of receipt, if transmitted by facsimile
(if such transmission is on a Business Day; or otherwise, on the next Business
Day following such transmission). Any Holder may change its address by giving
notice to the Company and the Company may change its address by giving notice to
the Holders in the manner provided above.

                                       15

<PAGE>

             To the Company:          Regeneron Pharmaceuticals, Inc.
                                      777 Old Saw Mill Road
                                      Tarrytown, New York 10591
                                      Attention: General Counsel

             With a copy (which       Skadden, Arps, Slate, Meagher & Flom LLP
             shall not constitute     4 Time Square
             notice) to:              New York, NY 10036
                                      Attention: David J. Goldschmidt, Esq.

             To the Investor:         Novartis Pharma AG
                                      Lichtstrasse 35
                                      CH-4002 Basel
                                      Switzerland
                                      Attention: General Counsel

             With a copy to (which:   Novartis Corporation
             shall not constitute     608 Fifth Avenue
             notice) to               New York, New York 10020
                                      Attention: General Counsel and Deputy
                                      General Counsel

                  Section 3.10      Severability. If, under applicable laws, any
provision hereof is invalid or unenforceable, or otherwise directly or
indirectly affects the validity of any other material provision(s) of this
Agreement ("Severed Clause"), then, it is mutually agreed that this Agreement
shall endure except for the Severed Clause. The parties shall consult and use
their best efforts to agree upon a valid and enforceable provision which shall
be a reasonable substitute for such Severed Clause in light of the intent of
this Agreement.

                     [Remainder of page intentionally blank]

                                       16

<PAGE>

                  IN WITNESS WHEREOF, the parties have executed and delivered
this Agreement as of the date first above written.

                                    NOVARTIS PHARMA AG

                                    By: /s/ Joseph E. Mamie
                                        ------------------------------------
                                     Name: Joseph E. Mamie
                                     Title: Head Operational Treasury

                                    By: /s/ Kim Urdahl
                                        -------------------------------------
                                     Name: Kim Urdahl
                                     Title: Head of Legal, Primary Care

                                    REGENERON PHARMACEUTICALS, INC.

                                    By: /s/ Stuart Kolinski
                                        -------------------------------------
                                     Name: Stuart Kolinski
                                     Title: Vice President & General Counsel

                                       17

<PAGE>

                                 SCHEDULE 1.4(C)

Class D Convertible Preferred Stock Purchase Agreement dated as of August 31,
1990, between the Company and Amgen, Inc.

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00052-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00052-of-00352.parquet"}]]