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                                  WARRANT AGREEMENT



                                    BY AND BETWEEN

                           REGENERON PHARMACEUTICALS, INC.

                                         and

                                      AMGEN INC.



                              Dated as of April 15, 1996





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                                  TABLE OF CONTENTS


                                                                            PAGE


SECTION 1.    Warrant Certificates..........................................  1

SECTION 2.    Execution of Warrant Certificates.............................  1

SECTION 3.    Registration..................................................  1

SECTION 4.    Registration of Transfers and Exchanges.......................  1

SECTION 5.    Warrants; Exercise of Warrant.................................  2

SECTION 6.    Payment of Taxes..............................................  3

SECTION 7.    Mutilated or Missing Warrant Certificates.....................  3

SECTION 8.    Reservation of Warrant Shares.................................  4

SECTION 9.    Obtaining Stock Exchange Listings.............................  4

SECTION 10.   Adjustment of Exercise Price and Number of Warrant Shares
               Issuable.....................................................  4


    (a)  Adjustment for Change in Capital Stock.............................  5
    (b)  Adjustment for Rights Issue........................................  6
    (c)  Adjustment for Other Distributions.................................  7
    (d)  Adjustment for Common Stock Issue..................................  7
    (e)  Adjustment for Convertible Securities Issue........................  9
    (f)  Current Market Price............................................... 10
    (g)  Consideration Received............................................. 10
    (h)  When De Minimis Adjustment May Be Deferred......................... 11
    (i)  When No Adjustment Required........................................ 11
    (j)  Notice of Adjustment............................................... 11
    (k)  Voluntary Reduction................................................ 11
    (l)  Reorganization of Company.......................................... 12
    (m)  Company Determination Final........................................ 13
    (n)  When Issuance or Payment May Be Deferred........................... 13
    (o)  Adjustment in Number of Shares..................................... 13
    (p)  Form of Warrants................................................... 14

SECTION 11.   Fractional Interests.......................................... 14

SECTION 12.   Notices to Warrant holders.................................... 14


                                          i



SECTION 13.   Notices to Company and Warrant Holder......................... 15

SECTION 14.   Supplements and Amendments.................................... 16

SECTION 15.   Successors.................................................... 16

SECTION 16.   Termination................................................... 17

SECTION 17.   Governing Law................................................. 17

SECTION 18.   Benefits of This Agreement.................................... 17

SECTION 19.   Counterparts.................................................. 17

EXHIBIT A..................................................................  A-1


                                          ii



     THIS WARRANT AGREEMENT (the "AGREEMENT") is dated as of April 15, 1996 and
entered into by and between REGENERON PHARMACEUTICALS, INC., a New York
corporation (the "COMPANY"), and AMGEN INC., a Delaware corporation ("AMGEN").

     WHEREAS, the Company proposes to issue to Amgen, or its designee, Common
Stock Purchase Warrants, as hereinafter described (the "WARRANTS"), to purchase

up to an aggregate of 700,000 shares of Common Stock, $.001 par value (the
"COMMON STOCK"), of the Company (the Common Stock issuable on exercise of the
Warrants being referred to herein as the "WARRANT SHARES"), pursuant to a Stock
and Warrant Purchase Agreement dated as of the date hereof (the "PURCHASE
AGREEMENT").

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

     SECTION 1. WARRANT CERTIFICATES. The certificates evidencing the Warrants
(the "WARRANT CERTIFICATES") to be delivered pursuant to this Agreement shall be
in registered form only and shall be substantially in the form set forth in
EXHIBIT A attached hereto.

     SECTION 2. EXECUTION OF WARRANT CERTIFICATES. Warrant Certificates shall be
signed on behalf of the Company by its Chairman of the Board or its President or
a Vice President and by its Secretary or an Assistant Secretary under its
corporate seal. Each such signature upon the Warrant Certificates may be in the
form of a facsimile signature of the present or any future Chairman of the
Board, President, Vice President, Secretary or Assistant Secretary and may be
imprinted or otherwise reproduced on the Warrant Certificates and for that
purpose the Company may adopt and use the facsimile signature of any person who
shall have been Chairman of the Board, President, Vice President, Secretary or
Assistant Secretary, notwithstanding the fact that at the time the Warrant
Certificates shall be delivered or disposed of he shall have ceased to hold such
office. The seal of the Company may be in the form of a facsimile thereof and
may be impressed, affixed, imprinted or otherwise reproduced on the Warrant
Certificates.

     In case any officer of the Company who shall have signed any of the Warrant
Certificates shall cease to be such officer before the Warrant Certificates so
signed shall have been disposed of by the Company, such Warrant Certificates
nevertheless may be delivered or disposed of as though such person had not
ceased to be such officer of the Company; and any Warrant Certificate may be
signed on behalf of the Company by any person who, at the actual date of the
execution of such Warrant Certificate, shall be a proper officer of the Company
to sign such Warrant Certificate, although at the date of the execution of this
Warrant Agreement any such person was not such officer.

     SECTION 3. REGISTRATION. The Company shall number and register the Warrant
Certificates in a register as they are issued.

     SECTION 4. REGISTRATION OF TRANSFERS AND EXCHANGES. The Company shall from
time to time register the transfer of any outstanding Warrant Certificates in a
Warrant register to be maintained by the Company upon surrender of such Warrant
Certificates accompanied by


                                          1



a written instrument or instruments of transfer in form satisfactory to the
Company, duly executed by the registered holder or holders thereof or by the

duly appointed legal representative thereof or by a duly authorized attorney.
Upon any such registration of transfer, a new Warrant Certificate shall be
issued to the transferee(s) and the surrendered Warrant Certificate shall be
cancelled and disposed of by the Company.

     The Warrant holders agree that each certificate representing Warrant Shares
will bear the following legend:

     "THIS WARRANT AND THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
     REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE
     OFFERED, SOLD OR OTHERWISE TRANSFERRED, PLEDGED OR HYPOTHECATED UNLESS AND
     UNTIL, IN THE CASE OF THE SHARES, SUCH SHARES ARE REGISTERED UNDER SUCH ACT
     OR, IN THE CASE OF THIS WARRANT AND THE SHARES, AN OPINION OF COUNSEL
     REASONABLY SATISFACTORY TO THE COMPANY IS OBTAINED TO THE EFFECT THAT SUCH
     REGISTRATION IS NOT REQUIRED."

     The Warrant holders further agree that they shall not offer, sell or
otherwise transfer the Warrants or Warrant Shares in violation of the foregoing
legend.

     Warrant Certificates may be exchanged at the option of the holder(s)
thereof, when surrendered to the Company at its office for another Warrant
Certificate or other Warrant Certificates of like tenor and representing in the
aggregate a like number of Warrants. Warrant Certificates surrendered for
exchange shall be cancelled and disposed of by the Company.

     SECTION 5. WARRANTS; EXERCISE OF WARRANTS. Subject to the terms of this
Agreement, each holder of Warrants shall have the right, which may be exercised
commencing at the opening of business on April 16, 1996 and until 5:00 p.m., New
York time on April 15, 2001, to receive from the Company the number of fully
paid and nonassessable Warrant Shares which the holder may at the time be
entitled to receive on exercise of such Warrants and payment to the Company of
the Exercise Price (as defined below) then in effect for such Warrant Shares.
Each Warrant not exercised prior to 5:00 p.m., New York time, on April 15, 2001
shall become void and all rights thereunder and all rights in respect thereof
under this Agreement shall cease as of such time.

     A Warrant may be exercised upon surrender to the Company at its office
designated for such purpose (the address of which is set forth in SECTION 13
hereof) of the certificate or certificates evidencing the Warrants to be
exercised with the form of election to purchase duly filled in and signed, which
signature shall be guaranteed by a bank or trust company having an office or
correspondent in the United States or a broker or dealer which is a member of a
registered securities exchange or the National Association of Securities
Dealers, Inc., and upon payment to the Company of the exercise price (the
"EXERCISE PRICE") which is set forth in the form of Warrant Certificate attached
hereto as EXHIBIT A, subject to adjustment pursuant to SECTION 10, for the
number of Warrant Shares in respect of which such Warrants are


                                        2




then exercised.  Payment of the aggregate Exercise Price shall be made in cash
or by certified or official bank check payable to the order of the Company.

     Subject to the provisions of SECTION 6 hereof, upon such surrender of
Warrants and payment of the Exercise Price the Company shall issue and cause to
be delivered with all reasonable dispatch to or upon the written order of the
holder and in such name or names as the Warrant holder may designate, a
certificate or certificates for the number of full Warrant Shares issuable upon
the exercise of such Warrants together with cash as provided in SECTION 11;
PROVIDED, HOWEVER, that if any reclassification, consolidation, merger or lease
or sale of assets is proposed to be effected by the Company as described in
subsection (l) of SECTION 10 hereof, or a tender offer or an exchange offer for
shares of Common Stock of the Company shall be made, upon such surrender of
Warrants and payment of the Exercise Price as aforesaid, the Company shall, as
soon as possible, but in any event not later than two business days thereafter,
issue and cause to be delivered the full number of Warrant Shares issuable upon
the exercise of such Warrants in the manner described in this sentence together
with cash as provided in SECTION 11. Such certificate or certificates shall be
deemed to have been issued and any person so designated to be named therein
shall be deemed to have become a holder of record of such Warrant Shares as of
the date of the surrender of such Warrants and payment of the Exercise Price.

     The Warrants shall be exercisable, at the election of the holders thereof,
either in full or from time to time in part and, in the event that a certificate
evidencing Warrants is exercised in respect of fewer than all of the Warrant
Shares issuable on such exercise at any time prior to the date of expiration of
the Warrants, a new certificate evidencing the remaining Warrant or Warrants
will be issued and delivered pursuant to the provisions of this Section and of
SECTION 2 hereof.

     All Warrant Certificates surrendered upon exercise of Warrants shall be
cancelled and disposed of by the Company. The Company shall keep copies of this
Agreement and any notices given or received hereunder available for inspection
by the holders during normal business hours at its office.

     SECTION 6. PAYMENT OF TAXES. The Company will pay all documentary stamp
taxes, if any, attributable to the initial issuance of Warrant Shares upon the
exercise of Warrants.

     SECTION 7. MUTILATED OR MISSING WARRANT CERTIFICATES. In case any of the
Warrant Certificates shall be mutilated, lost, stolen or destroyed, the Company
may in its discretion issue, in exchange and substitution for and upon
cancellation of the mutilated Warrant Certificate, or in lieu of and
substitution for the Warrant Certificate lost, stolen or destroyed, a new
Warrant Certificate of like tenor and representing an equivalent number of
Warrants, but only upon receipt of evidence reasonably satisfactory to the
Company of such loss, theft or destruction of such Warrant Certificate and
indemnity, if requested, also reasonably satisfactory to it. Applicants for such
substitute Warrant Certificates shall also comply with such other reasonable
regulations and pay such other reasonable charges as the Company may prescribe.


                                        3




     SECTION 8. RESERVATION OF WARRANT SHARES. The Company will at all times
reserve and keep available, free from preemptive rights, out of the aggregate of
its authorized but unissued Common Stock or its authorized and issued Common
Stock held in its treasury, for the purpose of enabling it to satisfy any
obligation to issue Warrant Shares upon exercise of the Warrants, the maximum
number of shares of Common Stock which may then be deliverable upon the exercise
of all the outstanding Warrants.

     The Company or, if appointed, the transfer agent for the Common Stock (the
"TRANSFER AGENT") and every subsequent transfer agent for any shares of the
Company's capital stock issuable upon the exercise of any of the rights of
purchase aforesaid will be irrevocably authorized and directed at all times to
reserve such number of authorized shares as shall be required for such purpose.
The Company will keep a copy of this Agreement on file with the Transfer Agent
and with every subsequent transfer agent for any shares of the Company's capital
stock issuable upon the exercise of the rights of purchase represented by the
Warrants. The Company will furnish such Transfer Agent a copy of all notices of
adjustments and certificates related thereto, transmitted to each holder
pursuant to SECTION 12 hereof.

     Before taking any action which would cause an adjustment pursuant to
SECTION 10 hereof to reduce the Exercise Price below the then par value (if any)
of the Warrant Shares, the Company will take any corporate action which may, in
the opinion of its counsel, be necessary in order that the Company may validly
and legally issue fully paid and nonassessable Warrant Shares at the Exercise
Price as so adjusted.

     The Company covenants that all Warrant Shares which may be issued upon
exercise of Warrants will, upon issue, be fully paid, nonassessable, free of
preemptive rights and free from all documentary stamp taxes, liens, charges and
security interests with respect to the issue thereof.

     SECTION 9. OBTAINING STOCK EXCHANGE LISTINGS. The Company will from time to
time take all action which may be necessary so that the Warrant Shares,
immediately upon their issuance upon the exercise of Warrants, will be listed on
the principal securities exchanges and markets within the United States of
America, if any, on which other shares of Common Stock are then listed.

     SECTION 10. ADJUSTMENT OF EXERCISE PRICE AND NUMBER OF WARRANT SHARES
ISSUABLE. The Exercise Price and the number of Warrant Shares issuable upon the
exercise of each Warrant are subject to adjustment from time to time upon the
occurrence of the events enumerated in this SECTION 10. For purposes of this
SECTION 10, "COMMON STOCK" means shares now or hereafter authorized of any class
of common stock of the Company and any other stock of the Company, however
designated, that has the right (subject to any prior rights of any class or
series of preferred stock) to participate in any distribution of the assets or
earnings of the Company without limit as to per share amount, including, without
limitation, the Class A Common Stock, par value $.001, of the Company.


                                        4




          ADJUSTMENT FOR CHANGE IN CAPITAL STOCK.

          If the Company:

          1. pays a dividend or makes a distribution on its Common Stock in
     shares of its Common Stock;

          2. subdivides its outstanding shares of Common Stock into a greater
     number of shares; or

          3. combines its outstanding shares of Common Stock into a smaller
     number of shares;

then the Exercise Price in effect immediately prior to such action shall then be
adjusted in accordance with the formula:

                        1      O
                       E = E x -
                               A

Where:
      1
     E =  the adjusted Exercise Price

     E =  the current Exercise Price

     O =  the number of shares of Common Stock outstanding prior to such action

     A =  the number of shares of Common Stock outstanding immediately after 
          such action

     In the case of a dividend or distribution the adjustment shall become
effective immediately after the record date for determination of holders of
shares of Common Stock entitled to receive such dividend or distribution, and in
the case of a subdivision or combination, the adjustment shall become effective
immediately after the effective date of such corporate action.

     If after an adjustment a holder of a Warrant upon exercise of it may
receive shares of two or more classes of capital stock of the Company, the
Company shall determine the allocation of the adjusted Exercise Price between
the classes of capital stock. After such allocation, the exercise privilege, the
number of shares issuable upon such exercise, and the Exercise Price of each
class of capital stock shall thereafter be subject to adjustment on terms
comparable to those applicable to Common Stock in this Section 10.


                                        5



     Such adjustment shall be made successively whenever any event listed above
shall occur.


     (b) ADJUSTMENT FOR RIGHTS ISSUE.

     If the Company distributes any rights, options or warrants to all holders
of its Common Stock entitling them at any time after the record date mentioned
below to purchase shares of Common Stock at a price per share less than the
Current Market Price (as defined in SECTION 10(f)) per share of Common Stock on
that record date, the Exercise Price shall be adjusted in accordance with the
formula:

                                N x P
                            O + -----
                        1         M
                       E  = E x -----
                                O + N


where:
       1
     E  = the adjusted Exercise Price.

     E  = the current Exercise Price.

     O  = the number of shares of Common Stock outstanding on the record date.

     N  = the number of additional shares of Common Stock issuable upon exercise
          of the rights, options or warrants offered.

     P  = the exercise price per share of the additional shares issuable upon 
          exercise of the rights, options or warrants.

     M  = the Current Market Price per share of Common Stock on the record date.

     The adjustment shall be made successively whenever any such rights, options
or warrants are issued and shall become effective immediately after the record
date for the determination of stockholders entitled to receive the rights,
options or warrants. If at the end of the period during which such rights,
options or warrants are exercisable, not all rights, options or warrants shall
have been exercised, the Exercise Price shall be immediately readjusted to what
it would have been if "N" in the above formula had been the number of shares
actually issued.


                                        6



     (c) ADJUSTMENT FOR OTHER DISTRIBUTIONS.

     If the Company distributes to all holders of its Common Stock any of its
assets (including but not limited to securities and cash), debt securities,
capital stock, or any rights or warrants to purchase assets, debt securities,
capital stock, or other securities of the Company, the Exercise Price shall be
adjusted in accordance with the formula:


                         1       M - F
                        E  = E x -----
                                   M

where:
       1
     E  = the adjusted Exercise Price.

     E  = the current Exercise Price.

     M  = the Current Market Price per share of Common Stock on the record date 
          mentioned below.

     F  = the fair market value on the record date of the assets, debt 
          securities, capital stock or rights or warrants applicable to one 
          share of Common Stock.  The Board of Directors shall determine the
          fair market value.

     The adjustment shall be made successively whenever any such distribution is
made and shall become effective immediately after the record date for the
determination of stockholders entitled to receive the distribution.

     This subsection does not apply to (i) dividends, distributions,
combinations or issuances referred to in subsection (a) of this SECTION 10, (ii)
rights, options or warrants referred to in subsection (b) of this SECTION 10, or
(iii) non-extraordinary quarterly cash dividends distributed to all holders of
Common Stock.

     (d) ADJUSTMENT FOR COMMON STOCK ISSUE.

     If the Company issues shares of Common Stock for a consideration per share
less than the Current Market Price per share of Common Stock on the date the
Company fixes the offering price of such additional shares, the Exercise Price
shall be adjusted in accordance with the formula:


                                        7



                                       P
                                  O + ---
                          1            M
                         E  = E x -------
                                     A

where:

       1
     E  = the adjusted Exercise Price.

     E  = the then current Exercise Price.


     O  = the number of shares outstanding immediately prior to the issuance of 
          such additional shares.

     P  = the aggregate consideration received for the issuance of such 
          additional shares.

     M  = the Current Market Price per share of Common Stock on the date of
          issuance of such additional shares.

     A  = the number of shares outstanding immediately after the issuance of 
          such additional shares.

     The adjustment shall be made successively whenever any such issuance is
made, and shall become effective immediately after such issuance.

     This subsection (d) does not apply to:

          (1) the exercise of Warrants,

          (2) rights, options, warrants or other distributions referred to in
     subsections (b), (c) or (e) of this SECTION 10,

          (3) Common Stock issued to the Company's directors, employees and
     non-employee service providers under bona fide benefit plans adopted by the
     Board of Directors and approved by the holders of Common Stock when
     required by law, if such Common Stock would otherwise be covered by this
     subsection (d), or

          (4) Common Stock issued in a bona fide public offering pursuant to a
     firm commitment underwriting.

          (5) issuances of shares of Common Stock for a consideration per share
     less than 100%, but greater than 92%, of the Current Market Price per share
     of Common Stock on the date the Company fixes the offering price of such
     additional shares.


                                        8



     (e) ADJUSTMENT FOR CONVERTIBLE SECURITIES ISSUE.

     If the Company issues any securities convertible into or exchangeable for
Common Stock (other than securities issued in transactions described in
subsections (b) and (c) of this SECTION 10) for a consideration per share of
Common Stock initially deliverable upon conversion or exchange of such
securities less than the Current Market Price per share of Common Stock on the
date of issuance of such securities, the Exercise Price shall be adjusted in
accordance with this formula:

                                        P
                                  O + -----
                          1             M

                         E  = E x ---------
                                    O + D


where:
       1
     E  = the adjusted Exercise Price.

     E  = the then current Exercise Price.

     O  = the number of shares outstanding immediately prior to the issuance of 
          such securities.

     P  = the aggregate consideration received for the issuance of such
          securities.

     M  = the Current Market Price per share of Common Stock on the date of
          issuance of such securities.

     D  = the maximum number of shares deliverable upon conversion or in 
          exchange for such securities at the initial conversion or exchange 
          rate.

     The adjustment shall be made successively whenever any such issuance is
made, and shall become effective immediately after such issuance.

     If all of the Common Stock deliverable upon conversion or exchange of such
securities have not been issued when such securities are no longer outstanding,
then the Exercise Price shall promptly be readjusted to the Exercise Price which
would then be in effect had the adjustment upon the issuance of such securities
been made on the basis of the actual number of shares of Common Stock issued
upon conversion or exchange of such securities.


                                        9



     This subsection (e) does not apply to convertible securities issued in a
bona fide public offering pursuant to a firm commitment underwriting, nor does
this subsection apply to issuances of any securities convertible into or
exchangeable for Common Stock for a consideration per share of Common Stock
initially deliverable upon conversion or exchange of such securities less than
100%, but greater than 92%, of the Current Market Price per share of Common
Stock on the date of issuance of such securities.

     (f) CURRENT MARKET PRICE.

     As used in this Agreement, the "Current Market Price" per share of Common
Stock on any date is the average of the Quoted Prices of the Common Stock for 30
consecutive trading days commencing 45 trading days before the date in question.
The "Quoted Price" of the Common Stock is the last reported sales price of the
Common Stock as reported by Nasdaq National Market, or if the Common Stock is
listed on a national securities exchange, the last reported sales price of the

Common Stock on such exchange (which shall be for consolidated trading if
applicable to such exchange), or if neither so reported or listed, the last
reported bid price of the Common Stock. In the absence of one or more such
quotations, the Board of Directors of the Company shall determine the Current
Market Price on the basis of such quotations as it in good faith considers
appropriate.

     (g) CONSIDERATION RECEIVED.

     For purposes of any computation respecting consideration received pursuant
to subsections (d) and (e) of this SECTION 10, the following shall apply:

          (1) in the case of the issuance of shares of Common Stock for cash,
     the consideration shall be the amount of such cash, provided that in no
     case shall any deduction be made for any commissions, discounts or other
     expenses incurred by the Company for any underwriting of the issue or
     otherwise in connection therewith;

          (2) in the case of the issuance of shares of Common Stock for a
     consideration in whole or in part other than cash, the consideration other
     than cash shall be deemed to be the fair market value thereof as determined
     in good faith by the Board of Directors (irrespective of the accounting
     treatment thereof), whose determination shall be conclusive, and described
     in a Board resolution; and

          (3) in the case of the issuance of securities convertible into or
     exchangeable for shares, the aggregate consideration received therefor
     shall be deemed to be the consideration received by the Company for the
     issuance of such securities plus the additional minimum consideration, if
     any, to be received by the Company upon the conversion or exchange thereof
     (the consideration in each case to be determined in the same manner as
     provided in clauses (1) and (2) of this subsection).


                                       10



     (h) WHEN DE MINIMIS ADJUSTMENT MAY BE DEFERRED.

     No adjustment in the Exercise Price need be made unless the adjustment
would require an increase or decrease of at least 1% in the Exercise Price. Any
adjustments that are not made shall be carried forward and taken into account in
any subsequent adjustment.

     All calculations under this Section shall be made to the nearest cent or to
the nearest 1/100th of a share, as the case may be.

     (i) WHEN NO ADJUSTMENT REQUIRED.

     No adjustment need be made for a transaction referred to in subsections
(a), (b), (c), (d) or (e) of this SECTION 10 if Warrant holders are to
participate in the transaction on a basis and with notice that the Board of
Directors determines to be fair and appropriate in light of the basis and notice

on which holders of Common Stock participate in the transaction.

     No adjustment need be made for rights to purchase Common Stock pursuant to
a Company plan for reinvestment of dividends or interest.

     No adjustment need be made for a change in the par value or no par value of
the Common Stock.

     If the Company distributes or issues rights to all holders of its Common
Stock pursuant to a shareholder rights plan, then no adjustment shall be made
pursuant to this SECTION 10 upon such distribution or issuance if, upon exercise
of the Warrants, each holder thereof receives the same type and number of
unexpired rights it would have received (as adjusted for any event described in
SECTION 10(a) OR 10(l)) had it exercised its Warrants, and been a holder of the
Warrant Shares issuable upon exercise thereof, prior to the record date for such
distribution or issuance.

     To the extent Warrants become convertible into cash, no adjustment need be
made thereafter as to the cash. Interest will not accrue on the cash.

     (j) NOTICE OF ADJUSTMENT.

     Whenever the Exercise Price is adjusted, the Company shall provide the
notices required by SECTION 12 hereof.

     (k) VOLUNTARY REDUCTION.

     The Company from time to time may reduce the Exercise Price by any amount
for any period of time if the period is at least 20 days and if the reduction is
irrevocable during the period; PROVIDED, HOWEVER, that in no event may the
Exercise Price be less than the par value of a share of Common Stock.


                                       11



     Whenever the Exercise Price is reduced pursuant to SUBSECTION 10(k), the
Company shall mail to Warrant holders a notice of the reduction. The Company
shall mail the notice at least 15 days before the date the reduced Exercise
Price takes effect. The notice shall state the reduced Exercise Price and the
period it will be in effect.

     A reduction of the Exercise Price does not change or adjust the Exercise
Price otherwise in effect for purposes of subsections (a), (b), (c), (d) and (e)
of this SECTION 10.

     (l) REORGANIZATION OF COMPANY.

     If any reclassification of the Common Stock of the Company or any
consolidation or merger of the Company with another entity, or the sale or lease
of all or substantially all of the Company's assets to another entity shall be
effected in such a way that holders of the Common Stock of the Company shall be
entitled to receive stock, securities or assets with respect to or in exchange

for such Common Stock, then, as a condition precedent to such reclassification,
consolidation, merger, sale or lease, lawful and adequate provisions shall be
made whereby the Warrant holder shall thereafter have the right to purchase and
receive upon the basis and the terms and conditions specified in this Agreement
and in lieu of the shares of Common Stock immediately theretofore purchasable
and receivable upon the exercise of the rights represented hereby, such shares
of stock, securities or assets as may be issued or payable in such
reclassification, consolidation, merger, sale or lease with respect to or in
exchange for the number of shares of Common Stock purchasable and receivable
upon the exercise of the rights represented hereby had such rights been
exercised immediately prior thereto, and in any such case appropriate provision
shall be made with respect to the rights and interests of the holders of the
Warrants to the end that the provisions hereof (including without limitation
provisions for adjustments of the Exercise Price and of the number of shares of
Common Stock purchasable and receivable upon the exercise of the Warrant) shall
thereafter be applicable, as nearly as may be, in relation to any shares of
stock, securities or assets thereafter deliverable upon the exercise hereof. The
Company will not effect any such reclassification, consolidation, merger, sale
or lease, unless prior to the consummation thereof the successor corporation (if
other than the Company) resulting from such reclassification, consolidation or
merger or the corporation purchasing or leasing such assets shall assume by a
supplemental Warrant Agreement, executed and mailed or delivered to the holders
of the Warrants at the last address thereof appearing on the books of Company,
the obligation to deliver to such holders such shares of stock, securities or
assets as, in accordance with the foregoing provisions, such holders may be
entitled to purchase.

     If the issuer of securities deliverable upon exercise of Warrants under the
supplemental Warrant Agreement is an affiliate of the formed, surviving,
transferee or lessee corporation, that issuer shall join in the supplemental
Warrant Agreement.

     If this subsection (l) applies, subsections (a), (b), (c), (d) and (e) of
this SECTION 10 do not apply.


                                       12



     (m) COMPANY DETERMINATION FINAL.

     Any determination that the Company or the Board of Directors must make
pursuant to this SECTION 10 is conclusive.

     (n) WHEN ISSUANCE OR PAYMENT MAY BE DEFERRED.

     In any case in which this SECTION 10 shall require that an adjustment in
the Exercise Price be made effective as of a record date for a specified event,
the Company may elect to defer until the occurrence of such event (i) issuing to
the holder of any Warrant exercised after such record date the Warrant Shares
and other capital stock of the Company, if any, issuable upon such exercise over
and above the Warrant Shares and other capital stock of the Company, if any,
issuable upon such exercise on the basis of the Exercise Price and (ii) paying

to such holder any amount in cash in lieu of a fractional share pursuant to
SECTION 11; PROVIDED, HOWEVER, that the Company shall deliver to such holder a
due bill or other appropriate instrument evidencing such holder's right to
receive such additional Warrant Shares, other capital stock and cash upon the
occurrence of the event requiring such adjustment.

     (o) ADJUSTMENT IN NUMBER OF SHARES.

     Upon each adjustment of the Exercise Price pursuant to this SECTION 10,
each Warrant outstanding prior to the making of the adjustment in the Exercise
Price shall thereafter evidence the right to receive upon payment of the
adjusted Exercise Price that number of shares of Common Stock (calculated to the
nearest hundredth) obtained from the following formula:

                                1        E
                               N  = N x ----
                                          1
                                         E

where:
      1
     N = the adjusted number of Warrant Shares issuable upon exercise of a
         Warrant by payment of the adjusted Exercise Price.

     N = the number of Warrant Shares previously issuable upon exercise of a 
         Warrant by payment of the Exercise Price prior to adjustment.
      1
     E = the adjusted Exercise Price.

     E = the Exercise Price prior to adjustment.


                                       13



     (p) FORM OF WARRANTS.

     Irrespective of any adjustments in the Exercise Price or the number or kind
of shares purchasable upon the exercise of the Warrants, Warrants theretofore or
thereafter issued may continue to express the same price and number and kind of
shares as are stated in the Warrants initially issuable pursuant to this
Agreement.

     SECTION 11. FRACTIONAL INTERESTS. The Company shall not be required to
issue fractional Warrant Shares on the exercise of Warrants. If more than one
Warrant shall be presented for exercise in full at the same time by the same
holder, the number of full Warrant Shares which shall be issuable upon the
exercise thereof shall be computed on the basis of the aggregate number of
Warrant Shares purchasable on exercise of the Warrants so presented. If any
fraction of a Warrant Share would, except for the provisions of this SECTION 11,
be issuable on the exercise of any Warrants (or specified portion thereof), the
Company shall pay an amount in cash equal to the Current Market Price on the day
immediately preceding the date the Warrant is presented for exercise, multiplied

by such fraction.

     SECTION 12. NOTICES TO WARRANT HOLDERS. Upon any adjustment of the Exercise
Price pursuant to SECTION 10, the Company shall promptly thereafter (i) cause to
be filed with the Company a certificate of a firm of independent public
accountants of recognized standing selected by the Board of Directors of the
Company (who may be the regular auditors of the Company) setting forth the
Exercise Price after such adjustment and setting forth in reasonable detail the
method of calculation and the facts upon which such calculations are based and
setting forth the number of Warrant Shares (or portion thereof) issuable after
such adjustment in the Exercise Price, upon exercise of a Warrant and payment of
the adjusted Exercise Price, which certificate shall be conclusive evidence of
the correctness of the matters set forth therein, and (ii) cause to be given to
each of the registered holders of the Warrant Certificates at his address
appearing on the Warrant register written notice of such adjustments by first-
class mail, postage prepaid. Where appropriate, such notice may be given in
advance and included as a part of the notice required to be mailed under the
other provisions of this SECTION 12.

     In case:

          (a) the Company shall authorize the issuance to all holders of shares
     of Common Stock of rights, options or warrants to subscribe for or purchase
     shares of Common Stock or of any other subscription rights or warrants; or

          (b) the Company shall authorize the distribution to all holders of
     shares of Common Stock of evidences of its indebtedness or assets (other
     than cash dividends or cash distributions payable out of earnings or earned
     surplus or dividends or distributions payable in shares of Common Stock);
     or

          (c) of any consolidation or merger to which the Company is a party and
     for which approval of any shareholders of the Company is required, or of
     the conveyance or transfer of all or substantially all of the properties
     and assets of the Company, or of


                                       14



     any reclassification or change of Common Stock issuable upon exercise of
     the Warrants (other than a change in par value, or from par value to no par
     value, or from no par value to par value, or as a result of a subdivision
     or combination), or a tender offer or exchange offer for shares of Common
     Stock; or

          (d) of the voluntary or involuntary dissolution, liquidation or
     winding up of the Company; or

          (e) the Company proposes to take any action that would require an
     adjustment in the Exercise Price pursuant to subsections (a), (b), (c), (d)
     or (e) of SECTION 10 and if the Company does not arrange for Warrant
     holders to participate pursuant to subsection (i) of SECTION 10, or if the

     Company takes any action that would require a supplemental Warrant
     Agreement pursuant to subsection (l) of SECTION 10,

then the Company shall cause to be given to each of the registered holders of
the Warrant Certificates at his address appearing on the Warrant register, at
least 20 days (or 10 days in any case specified in clauses (a), (b) or (c)
above) prior to the applicable record date hereinafter specified, or promptly in
the case of events for which there is no record date, by first-class mail,
postage prepaid, a written notice stating (i) the date as of which the holders
of record of shares of Common Stock to be entitled to receive any such rights,
options, warrants or distribution are to be determined, or (ii) the initial
expiration date set forth in any tender offer or exchange offer for shares of
Common Stock, or (iii) the date on which any such consolidation, merger,
conveyance, transfer, dissolution, liquidation or winding up is expected to
become effective or consummated, and the date as of which it is expected that
holders of record of shares of Common Stock shall be entitled to exchange such
shares for securities or other property, if any, deliverable upon such
reclassification, consolidation, merger, conveyance, transfer, dissolution,
liquidation or winding up.  The failure to give the notice required by this
SECTION 12 or any defect therein shall not affect the legality or validity of
any distribution, right, option, warrant, consolidation, merger, conveyance,
transfer, dissolution, liquidation or winding up, or the vote upon any action.

     Nothing contained in this Agreement or in any of the Warrant Certificates
shall be construed as conferring upon the holders thereof the right to vote or
to consent or to receive notice as shareholders in respect of the meetings of
shareholders or the election of Directors of the Company or any other matter, or
any rights whatsoever as shareholders of the Company.

     SECTION 13. NOTICES TO COMPANY AND WARRANT HOLDER. Unless otherwise
provided herein, any notice, request, instruction or other document to be given
hereunder by any party to the others shall be in writing and delivered in person
or by courier, telegraphed, telexed or by facsimile transmission (with receipt
confirmed), or mailed by certified mail, postage prepaid, return receipt
requested (such mailed notice to be effective on the date such receipt is
acknowledged), as follows:


                                       15



     If to the Company:

             Regeneron Pharmaceuticals, Inc.
             777 Old Saw Mill River Road
             Tarrytown, New York 10591-6707
             Attn: Corporate Secretary
             Telecopy No.: (914) 345-7721

     With a copy to:

             Skadden, Arps, Slate, Meagher & Flom
             919 Third Avenue

             New York, New York 10022
             Attn: Morris Kramer, Esq.
             Telecopy No.: (212) 735-2000

     If to Warrant Holder:

             Amgen Inc.
             Amgen Center
             1840 DeHavilland Drive
             Thousand Oaks, California 91320
             Attn: The Corporate Secretary
             Telecopy No.: (805) 499-9315

     With a copy to:

             Latham & Watkins
             633 West Fifth Street, Suite 4000
             Los Angeles, California 90071
             Attn: Michael W. Sturrock, Esq.
             Telecopy No.: (213) 891-8763

or to such other place and with such other copies as either party may designate
as to itself by written notice to the others.

     SECTION 14. SUPPLEMENTS AND AMENDMENTS. The Company may not supplement or
amend this Agreement without the prior written approval of the holders of
Warrant Certificates affected by such supplement or amendment.

     SECTION 15. SUCCESSORS. All the covenants and provisions of this Agreement
by or for the benefit of the Company shall bind and inure to the benefit of its
respective successors and assigns hereunder.


                                       16



     SECTION 16. TERMINATION. This Agreement shall terminate at 5:00 p.m., New
York time on April 15, 2001. Notwithstanding the foregoing, this Agreement will
terminate on any earlier date if all Warrants have been exercised.

     SECTION 17. GOVERNING LAW. This Agreement and each Warrant Certificate
issued hereunder shall be deemed to be a contract made under the laws of the
State of New York and for all purposes shall be construed in accordance with the
internal laws of said State.

     SECTION 18. BENEFITS OF THIS AGREEMENT. Nothing in this Agreement shall be
construed to give to any person or corporation other than the Company and the
registered holders of the Warrant Certificates any legal or equitable right,
remedy or claim under this Agreement; but this Agreement shall be for the sole
and exclusive benefit of the Company and the registered holders of the Warrant
Certificates.

     SECTION 19. COUNTERPARTS. This Agreement may be executed in any number of

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

                           [Signature Page To Follow]


                                       17



     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed, as of the day and year first above written.


                                       REGENERON PHARMACEUTICALS, INC.



                                       By:
                                          -------------------------------------
                                          Name:  Leonard S. Schleifer
                                          Title: President

- -----------------------------------
Seal




Attest:
         --------------------------
              Secretary


                                       AMGEN INC.



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

- -----------------------------------
Seal




Attest:
         --------------------------
              Secretary



                                       S-1



                                                                       EXHIBIT A

                          [Form of Warrant Certificate]

THIS WARRANT AND THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE OFFERED,
SOLD OR OTHERWISE TRANSFERRED, PLEDGED OR HYPOTHECATED UNLESS AND UNTIL, WITH
RESPECT TO THE SHARES, SUCH SHARES ARE REGISTERED UNDER SUCH ACT OR, WITH
RESPECT TO THIS WARRANT OR THE SHARES, AN OPINION OF COUNSEL REASONABLY
SATISFACTORY TO THE COMPANY IS OBTAINED TO THE EFFECT THAT SUCH REGISTRATION IS
NOT REQUIRED.

     EXERCISABLE ON OR BEFORE 5:00 P.M., NEW YORK TIME, APRIL 15, 2001

No.                                                             700,000 Warrants

                               Warrant Certificate

                         REGENERON PHARMACEUTICALS, INC.

     This Warrant Certificate certifies that Amgen, Inc., or registered assigns,
is the registered holder of 700,000 Warrants expiring April 15, 2001 (the
"WARRANTS") to purchase Common Stock, $.001 par value (the "COMMON STOCK"), of
REGENERON PHARMACEUTICALS, INC., a New York corporation (the "COMPANY"). Each
Warrant entitles the holder to receive from the Company upon exercise on or
before 5:00 p.m. New York Time on April 15, 2001, one fully paid and
nonassessable share of Common Stock (a "WARRANT SHARE") at the initial exercise
price (the "EXERCISE PRICE") of $16.00 payable in lawful money of the United
States of America upon surrender of this Warrant Certificate and payment of the
Exercise Price at the office of the Company designated for such purpose, subject
to the conditions set forth herein and in the Warrant Agreement referred to
herein. The Exercise Price and number of Warrant Shares issuable upon exercise
of the Warrants are subject to adjustment upon the occurrence of certain events
set forth in the Warrant Agreement.

     No Warrant may be exercised after 5:00 p.m., New York Time on April 15,
2001, and to the extent not exercised by such time such Warrants shall become
void.


                                       A-1



     The Warrants evidenced by this Warrant Certificate are issued pursuant to a
Warrant Agreement dated as of April 15, 1996 (the "WARRANT AGREEMENT"), duly
executed and delivered by the Company, which Warrant Agreement is hereby
incorporated by reference in and made a part of this instrument and is hereby
referred to for a description of the rights, limitation of rights, obligations,

duties and immunities thereunder of the Company and the holders (the words
"holders" or "holder" meaning the registered holders or registered holder) of
the Warrants. A copy of the Warrant Agreement may be obtained by the holder
hereof upon written request to the Company.

     Warrants may be exercised at any time on or before 5:00 p.m., New York time
on April 15, 2001. The holder of Warrants evidenced by this Warrant Certificate
may exercise them by surrendering this Warrant Certificate, with the form of
election to purchase set forth hereon properly completed and executed, together
with payment of the Exercise Price at the office of the Company designated for
such purpose. In the event that upon any exercise of Warrants evidenced hereby
the number of Warrants exercised shall be less than the total number of Warrants
evidenced hereby, there shall be issued to the holder hereof or his assignee a
new Warrant Certificate evidencing the number of Warrants not exercised. No
adjustment shall be made for any dividends on any Common Stock issuable upon
exercise of this Warrant.

     The Warrant Agreement provides that upon the occurrence of certain events
the Exercise Price set forth on the face hereof may, subject to certain
conditions, be adjusted. If the Exercise Price is adjusted, the Warrant
Agreement provides that the number of shares of Common Stock issuable upon the
exercise of each Warrant shall be adjusted. No fractions of a share of Common
Stock will be issued upon the exercise of any Warrant, but the Company will pay
the cash value thereof determined as provided in the Warrant Agreement.

     The holders of Warrants are entitled to certain registration rights with
respect to the Common Stock purchasable upon exercise thereof. Said registration
rights are set forth in full in a Registration Rights Agreement dated as of
April 15, 1996, between the Company and Amgen. A copy of the Registration Rights
Agreement may be obtained by the holder hereof upon written request to the
Company.

     Warrant Certificates, when surrendered at the office of the Company by the
registered holder thereof in person or by legal representative or attorney duly
authorized in writing, may be exchanged, in the manner and subject to the
limitations provided in the Warrant Agreement, but without payment of any
service charge, for another Warrant Certificate or Warrant Certificates of like
tenor evidencing in the aggregate a like number of Warrants.

     Upon due presentation for registration of transfer of this Warrant
Certificate at the office of the Company a new Warrant Certificate or Warrant
Certificates of like tenor and evidencing in the aggregate a like number of
Warrants shall be issued to the transferee(s) in exchange for this Warrant
Certificate, subject to the limitations provided in the Warrant Agreement,
without charge except for any tax or other governmental charge imposed in
connection therewith.


                                       A-2



     The Company may deem and treat the registered holder(s) thereof as the
absolute owner(s) of this Warrant Certificate (notwithstanding any notation of

ownership or other writing hereon made by anyone), for the purpose of any
exercise hereof, of any distribution to the holder(s) hereof, and for all other
purposes, and the Company shall not be affected by any notice to the contrary.
Neither the Warrants nor this Warrant Certificate entitles any holder hereof to
any rights of a stockholder of the Company.

     This Warrant Certificate shall not be valid unless countersigned by the
Company, as such term is used in the Warrant Agreement.

     This Warrant Certificate shall not be offered, sold or otherwise
transferred in violation of the legend on the first page hereof.

                           [Signature Page To Follow]


                                       A-3



     IN WITNESS WHEREOF, the Company has caused this Warrant Certificate to be
signed by its President and by its Secretary and has caused its corporate seal
to be affixed hereunto or imprinted hereon.

Dated:  April 15, 1996


                                     REGENERON PHARMACEUTICALS, INC.



                                     By:
                                        ---------------------------------------
                                        Name:  Leonard S. Schleifer
                                        Title:  President



                                     By:
                                        ----------------------------------------
                                        Name:  Paul Lubetkin
                                        Title:  Secretary


                                       S-1



                          [Form of Election to Purchase

                    (To Be Executed Upon Exercise Of Warrant)

     The undersigned hereby irrevocably elects to exercise the right,
represented by this Warrant Certificate, to receive _________ shares of Common
Stock and herewith tenders payment for such shares to the order of REGENERON

PHARMACEUTICALS, INC. in the amount of $_________ in accordance with the terms
hereof. The undersigned requests that a certificate for such shares be
registered in the name of ________________, whose address is
_______________________________ and that such shares be delivered to
________________ whose address is _________________________________. If said
number of shares is less than all of the shares of Common Stock purchasable
hereunder, the undersigned requests that a new Warrant Certificate representing
the remaining balance of such shares be registered in the name of
______________, whose address is _________________________, and that such
Warrant Certificate be delivered to _________________, whose address is
__________________.


                                     Signature:
                                               ---------------------------------


Date:
      ------------------------


                                   Signature Guaranteed:
                                                        ------------------------