REGENERON PHARMACEUTICALS INC, S-3/A, 2000-03-10

REGENERON PHARMACEUTICALS INC
S-3/A, 2000-03-10
PHARMACEUTICAL PREPARATIONS

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<PAGE>

AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON MARCH 10, 2000

REGISTRATION NO. 333-31764

- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

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

AMENDMENT NO. 1
TO
FORM S-3
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

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

REGENERON PHARMACEUTICALS, INC.
(EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

NEW YORK 13-3444607
(STATE OR OTHER JURISDICTION OF (I.R.S. EMPLOYER
INCORPORATION OR ORGANIZATION) IDENTIFICATION NO.)

777 OLD SAW MILL RIVER ROAD
TARRYTOWN, NEW YORK 10591-6707
(914) 347-7000
(ADDRESS, INCLUDING ZIP CODE AND TELEPHONE NUMBER,
INCLUDING AREA CODE, OF REGISTRANT'S PRINCIPAL EXECUTIVE OFFICES)

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

MURRAY A. GOLDBERG
CHIEF FINANCIAL OFFICER
REGENERON PHARMACEUTICALS, INC.
777 OLD SAW MILL RIVER ROAD
TARRYTOWN, NEW YORK 10591-6707
(914) 347-7000
(NAME, ADDRESS, INCLUDING ZIP CODE AND TELEPHONE NUMBER,
INCLUDING AREA CODE, OF AGENT FOR SERVICE)

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

Copies to:

MATTHEW J. MALLOW, ESQ. JI HOON HONG, ESQ.
DAVID J. GOLDSCHMIDT, ESQ. SHEARMAN & STERLING
SKADDEN, ARPS, SLATE, MEAGHER & FLOM LLP 599 LEXINGTON AVENUE
FOUR TIMES SQUARE NEW YORK, NEW YORK 10022-6069
NEW YORK, NEW YORK 10036-6522 (212) 848-4000
(212) 735-3000

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

APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: As soon as
practicable after this Registration Statement becomes effective.

If the only securities being registered on this form are being offered
pursuant to dividend or interest reinvestment plans, please check the following
box. / /

If any of the securities being registered on this Form are to be offered on
a delayed or continuous basis pursuant to Rule 415 under the Securities Act of
1933, other than securities offered only in connection with dividend or interest
reinvestment plans, check the following box. / /

If this form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list the Securities Act registration statement number of the earlier
effective registration statement for the same offering. / /

If this form is a post-effective amendment filed pursuant to Rule
462(c) under the Securities Act, check the following box and list the Securities
Act registration statement number of the earlier effective registration
statement for the same offering. / /

If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box. / /
------------------------

THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR DATES
AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL FILE
A FURTHER AMENDMENT SPECIFICALLY STATING THAT THIS REGISTRATION STATEMENT SHALL
THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(A) OF THE SECURITIES
ACT OF 1933 OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME EFFECTIVE ON SUCH
DATE AS THE COMMISSION, ACTING PURSUANT TO SAID SECTION 8(A), MAY DETERMINE.

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

<PAGE>

The information in this prospectus is not complete and may be changed. We may
not sell these securities until the registration statement filed with the
Securities and Exchange Commission is effective. This prospectus is not an offer
to sell these securities and it is not soliciting an offer to buy these
securities in any state where the offer or sale is not permitted.

SUBJECT TO COMPLETION
PRELIMINARY PROSPECTUS DATED MARCH 10, 2000

PROSPECTUS

4,000,000 SHARES
REGENERON PHARMACEUTICALS, INC.
COMMON STOCK

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

Regeneron is selling 4,000,000 shares.

The shares are quoted on the Nasdaq National Market under the symbol
"REGN." On March 8, 2000, the last sale price of the shares as reported on the
Nasdaq National Market was $41 3/4 per share.

INVESTING IN THE COMMON STOCK INVOLVES RISKS THAT ARE DESCRIBED IN THE
"RISK FACTORS" SECTION BEGINNING ON PAGE 8 OF THIS PROSPECTUS.

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

PER SHARE TOTAL
---------- ------
Public offering price.................................. $ $
Underwriting discount.................................. $ $
Proceeds, before expenses, to Regeneron................ $ $

The underwriters may also purchase up to an additional 600,000 shares
from a selling shareholder at the public offering price, less the underwriting
discount, within 30 days from the date of this prospectus to cover
over-allotments.

Neither the Securities and Exchange Commission nor any state securities
commission has approved or disapproved of these securities or determined if this
prospectus is truthful or complete. Any representation to the contrary is a
criminal offense.

The shares will be ready for delivery on or about , 2000.

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

MERRILL LYNCH & CO.
LEHMAN BROTHERS
J.P. MORGAN & CO.
ROBERTSON STEPHENS

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

The date of this prospectus is , 2000.

<PAGE>

TABLE OF CONTENTS

PAGE
----
Summary................................................................. 3
Risk Factors............................................................ 8
This Prospectus Contains Forward-Looking Statements..................... 17
Use of Proceeds......................................................... 17
Dividend Policy......................................................... 17
Capitalization.......................................................... 18
Dilution................................................................ 19
Selected Financial Data................................................. 20
Business................................................................ 21
Management.............................................................. 31
Investment Company Act Considerations................................... 34
Description of Capital Stock............................................ 34
Selling Shareholder..................................................... 37
Underwriting............................................................ 38
Legal Matters........................................................... 40
Experts................................................................. 41
Where You Can Find More Information..................................... 41

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

In this prospectus, "Regeneron," "our company," "we," "us" and "our" refer
to Regeneron Pharmaceuticals, Inc. You should rely only on the information
contained or incorporated by reference in this prospectus. We have not, and the
underwriters have not, authorized any other person to provide you with different
information. If anyone provides you with different or inconsistent information,
you should not rely on it. We are not, and the underwriters are not, making an
offer to sell these securities in any jurisdiction where the offer or sale is
not permitted. You should assume that the information appearing in this
prospectus is accurate only as of the date on the front cover of this
prospectus. Our business, financial condition, results of operations and
prospects may have changed since that date.

<PAGE>

SUMMARY

The following summary highlights information contained in other parts of
this prospectus or incorporated by reference in this prospectus. You should read
this summary together with the more detailed information elsewhere in this
prospectus and in our financial statements and accompanying notes and other
information incorporated by reference in this prospectus. Unless otherwise
indicated, all information in this prospectus assumes no exercise of the
underwriters' over-allotment option, gives no effect to the exercise of
outstanding options and warrants to purchase common stock, and assumes all share
numbers set forth in this prospectus are as of March 8, 2000.

REGENERON PHARMACEUTICALS, INC.

We are a biopharmaceutical company that discovers, develops and intends to
commercialize therapeutic drugs for the treatment of serious medical conditions.
Expanding from our initial focus on degenerative neurologic diseases, we have
more recently broadened our product pipeline to include drug candidates for the
treatment of obesity, rheumatoid arthritis, cancer, allergies, asthma, ischemia
and other diseases and disorders.

Our ability to discover and develop product candidates for a wide variety
of serious medical conditions results from the leveraging of several powerful
technology platforms, many of which were developed or enhanced by us. In
contrast to basic genomics approaches, which attempt to identify every gene in a
cell or genome, we use Targeted Genomics(TM) and Functionomics(TM) (functional
cloning) technology platforms that are designed to discover specific genes of
therapeutic interest for a particular disease or cell type. Using these
approaches, we have discovered many new families of growth factors and
receptors, many of which are already protected by issued patents and which have
led to several product candidates. If the natural protein itself is not a
product candidate, we utilize our Designer Protein Therapeutics(TM) platform to
genetically engineer product candidates with the desired properties. This
technology platform has already produced more than 10 patented proteins, several
of which are in preclinical development.

The sophisticated application of all of these technology platforms, coupled
with our biologic expertise in preclinical models of disease, has allowed us to
discover drug candidates that address a wide variety of important medical needs.
Relative to many participants in the biotechnology and genomics industry, we are
well-positioned with three products in ongoing clinical trials and several
product candidates planned to enter clinical trials over the next one to two
years, including:

o AXOKINE(R) SECOND GENERATION CILIARY NEUROTROPHIC FACTOR: Acts on the
brain region regulating food intake and energy expenditure. AXOKINE is
being developed for the treatment of obesity and complications of obesity
such as Type II diabetes and is in clinical trials. We are also
developing a modified form of AXOKINE (pegylated) that in preclinical
studies is substantially longer acting than unmodified AXOKINE. This may
allow less frequent and lower dosing in patients.

o CYTOKINE TRAPS: Protein-based antagonists for cytokines such as
interleukin-1 (called IL-1), interleukin-4 (IL-4) and interleukin-6
(IL-6) and a single antagonist that blocks both IL-4 and interleukin-13
(IL-13). These cytokines are thought to play a major role in diseases
such as rheumatoid arthritis and other inflammatory diseases, asthma,
allergic disorders and cancer. Cytokine Traps are potential treatments
for these diseases, and at least one Cytokine Trap is expected to enter
clinical trials by 2001.

o VEGF TRAP: An antagonist to Vascular Endothelial Growth Factor (called
VEGF), which is required for the growth of blood vessels that are needed
for tumors to grow. In a preclinical model of cancer, the VEGF Trap
blocked the growth of tumors by an anti-angiogenesis mechanism. VEGF Trap
is a potential treatment for cancer and is expected to enter clinical
trials in 2001.

o ANGIOPOIETINS: A new family of growth factors, discovered by us, that are
specific for blood vessels and early hemopoietic stem cells. The
Angiopoietins, and engineered forms of these growth factors that can act
as activators and blockers, are in preclinical testing for promoting
blood vessel growth (to provide blood flow in diseased hearts and other
tissues that have lost their original blood supplies), for blocking blood
vessel growth (for the treatment of cancers), for fixing leaky blood
vessels (that cause swelling and edema in many different diseases such as
stroke, diabetic retinopathy and inflammatory diseases), and for
promoting the growth and mobilization of certain hemopoietic cells such
as stem cells and platelets.

<PAGE>

o BRAIN-DERIVED NEUROTROPHIC FACTOR, OR BDNF: Promotes survival of the
spinal cord neurons that die in amyotrophic lateral sclerosis (or ALS,
commonly known as Lou Gehrig's Disease) in preclinical models. BDNF is in
clinical trials for ALS using two routes of administration; one of these
trials is based on the results of a prior Phase III clinical trial.

o NEUROTROPHIN-3, OR NT-3: Acts on the neurons of the intestinal tract and
is in clinical trial for the treatment of constipating disorders
associated with spinal cord injury and other neurologic diseases.

We are currently developing AXOKINE and our Cytokine Traps independently of
any corporate partners. We are developing BDNF in partnership with Amgen Inc.
and Sumitomo Pharmaceuticals Company, Ltd., NT-3 in partnership with Amgen and
our VEGF Trap, Angiopoietins and other product candidates in partnership with
The Procter & Gamble Company. In all of these partnerships, we retain 50% U.S.
commercialization rights. We also have numerous academic collaborations.

Our manufacturing facilities in Tarrytown, New York, and Rensselaer, New
York, were designed to comply with the Food and Drug Administration's current
good manufacturing practices (called GMP). The Tarrytown facility produces
preclinical and clinical supplies of our products and product candidates. At the
Rensselaer facility, we manufacture products for Sumitomo Pharmaceuticals and
Merck & Co., Inc. under contracts with them. We will continue to upgrade and
expand our manufacturing facilities as we advance our products toward
commercialization.

We believe that we possess a strong intellectual property position,
including 42 issued U.S. patents and more than 100 pending applications in all
key areas of our research and development, including angiogenesis, bone and
cartilage formation, Cytokine Traps, muscle atrophy and neurological disorders.
We have a policy to file patent applications to protect technology, inventions
and improvements we consider important to the development of our business. We
also rely on trade secrets, know-how and continuing technological innovation to
maintain and enhance our competitive position.

Each member of our senior management team has at least ten years of
experience in the biopharmaceutical industry. In addition, our Board of
Directors consists of noted business and scientific leaders, including the
former Chairman and CEO of Merck and three Nobel Laureates. In a 1997 survey by
the Institute for Scientific Information, our Chief Scientific Officer was
listed among the 11 most highly cited scientists and was the only non-academic
scientist in the group. We believe that we have been successful in attracting
skilled and experienced personnel in a highly competitive environment. As of
December 31, 1999, we had 437 full-time employees, 82 of whom hold a Ph.D. or
M.D. degree or both.

RECENT DEVELOPMENTS

We recently entered into a collaboration under a binding memorandum of
understanding with Medarex, Inc. to discover, develop and commercialize human
antibodies as therapeutics. We will contribute our expertise in discovering and
characterizing proteins as drug targets, and Medarex will contribute its HuMab-
Mouse(TM) technology to create fully human antibody products for those targets.
Together we have selected more than twenty initial targets, including growth
factors, cytokines, and receptors, and plan to add additional targets in the
future.

We have also recently signed an agreement with Emisphere Technologies, Inc.
to establish a research and development collaboration to utilize Emisphere's
oral drug delivery technology for AXOKINE. In preliminary preclinical
pharmacokinetic studies, the Emisphere technology was able to achieve measurable
blood levels of AXOKINE.

<PAGE>
SELECTED PRODUCTS AND PROGRAMS

<TABLE>
<CAPTION>
TECHNOLOGY PLATFORMS USED
FOR DISCOVERY AND
DEVELOPMENT PROGRAM AND PRODUCT TARGETED INDICATION STAGE COMMERCIALIZATION RIGHTS
- ------------------------- ------------------------- ----------------------- ------------ -------------------------
<S> <C> <C> <C> <C>
TARGETED GENOMICS AXOKINE(R) Second Obesity and Clinical Regeneron
DESIGNER PROTEIN Generation Ciliary complications of
THERAPEUTICS Neurotrophic Factor obesity such as Type II
diabetes

TARGETED GENOMICS BDNF (Brain-derived Amyotrophic lateral
Neurotrophic Factor) sclerosis (ALS)
Intrathecal (U.S.) Clinical Regeneron and Amgen
Subcutaneous (U.S.) Clinical Regeneron and Amgen
Subcutaneous (Japan) Clinical Sumitomo Pharmaceuticals

TARGETED GENOMICS NT-3 (Neurotrophin-3) Constipating conditions Clinical Regeneron and Amgen
associated with spinal
cord injury and other
medical conditions

CYTOKINE TRAPS
--------------

DESIGNER PROTEIN IL-1 Rheumatoid arthritis Preclinical Regeneron
THERAPEUTICS and other inflammatory
disorders

DESIGNER PROTEIN IL-4 Asthma and allergic Preclinical Regeneron
THERAPEUTICS disorders

DESIGNER PROTEIN IL-4/13 Asthma and allergic Preclinical Regeneron
THERAPEUTICS disorders

DESIGNER PROTEIN IL-2, IL-3, IL-5, IL-6, Multiple Research Regeneron
THERAPEUTICS IL-15, gamma-interferon,
TGF-beta and others

ANGIOGENESIS
------------

DESIGNER PROTEIN VEGF Trap Cancer Preclinical Regeneron and
THERAPEUTICS Procter & Gamble

TARGETED GENOMICS Angiopoietin-1 Ischemia, vascular Preclinical Regeneron and
FUNCTIONOMICS leak, edema and Procter & Gamble
DESIGNER PROTEIN hemopoiesis
THERAPEUTICS

TARGETED GENOMICS Ephrins, Angiopoietin-2 Cancer, ischemia and Research Regeneron and
FUNCTIONOMICS hemopoiesis Procter & Gamble

DESIGNER PROTEIN
THERAPEUTICS

TARGETED GENOMICS MUSCLE DISEASES AND Muscle atrophy and Research Regeneron and
FUNCTIONOMICS DISORDERS injury Procter & Gamble
-------------------

BONE AND CARTILAGE
------------------

TARGETED GENOMICS RORs Osteoarthritis Research Regeneron and
FUNCTIONOMICS Procter & Gamble

TARGETED GENOMICS DDRs Fibrosis and cirrhosis Research Regeneron and
FUNCTIONOMICS Procter & Gamble

TARGETED GENOMICS G-PROTEIN COUPLED Multiple targets Research Regeneron and
FUNCTIONOMICS RECEPTORS Procter & Gamble
-----------------
</TABLE>

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We are a New York corporation organized on January 8, 1988. Our executive
offices are at 777 Old Saw Mill River Road, Tarrytown, New York 10591-6707 and
our telephone number is (914) 347-7000.

5
<PAGE>

THE OFFERING

<TABLE>
<S> <C>
Common stock offered by Regeneron............ 4,000,000 shares
Shares outstanding after the offering:
Common stock............................... 33,641,005 shares
Class A stock.............................. 2,789,511 shares
Total................................... 36,430,516 shares

Use of proceeds.............................. We estimate that our net proceeds from this offering will be
approximately $158.1 million, assuming a public offering price of
$41.75 per share. We intend to use these net proceeds for working
capital and general corporate purposes, including:
o All of the costs to fund preclinical and clinical development of
product candidates that are being developed independent of any
corporate partner, such as AXOKINE and Cytokine Traps;
o Our share of the costs to fund preclinical and clinical
development of product candidates that have been partnered, such
as BDNF, NT-3, VEGF Trap and Angiopoietins;
o Basic research;
o Commercialization expenses;
o Purchase of equipment and expansion of manufacturing facilities;
and
o Potential acquisitions of companies and technologies which
complement our business.
Risk factors................................. See "Risk Factors" and other information included in this
prospectus for a discussion of factors you should carefully
consider before deciding to invest in shares of our common stock.
Nasdaq National Market symbol................ REGN
</TABLE>

The number of shares outstanding after the offering is derived from our
records and excludes (1) options to purchase 5,523,222 shares of our common
stock under our 1990 Long-Term Incentive Plan, of which 2,361,777 were
exercisable at March 8, 2000, (2) options to purchase 333,000 shares of our
common stock which have been granted subject to shareholder approval, and
(3) 1,557,400 warrants held by Procter & Gamble and Medtronic as of March 8,
2000. In addition, the number of shares outstanding includes those issued in
connection with the exercise of 700,000 warrants by Amgen on March 2, 2000.

Holders of our Class A stock are entitled to ten votes per share and the
holders of our common stock are entitled to one vote per share.

<PAGE>

SUMMARY SELECTED FINANCIAL DATA

<TABLE>
<CAPTION>
YEAR ENDED DECEMBER 31,
--------------------------------------------------------
1999 1998 1997 1996 1995
-------- -------- -------- -------- --------
(IN THOUSANDS, EXCEPT PER SHARE DATA)
<S> <C> <C> <C> <C> <C>
STATEMENT OF OPERATIONS DATA:
Revenues
Contract research and development.................. $ 24,539 $ 19,714 $ 17,400 $ 17,303 $ 23,247
Research progress payments......................... -- 9,500 5,000 -- --
Contract manufacturing............................. 9,960 9,113 4,458 2,451 1,140
Investment income.................................. 5,207 6,866 6,242 4,360 2,997
-------- -------- -------- -------- --------
39,706 45,193 33,100 24,114 27,384
-------- -------- -------- -------- --------
Expenses
Research and development........................... 44,940 37,047 27,770 28,269 23,310
Loss in Amgen-Regeneron Partners................... 4,159 2,484 3,403 14,250 13,805
General and administrative......................... 6,355 5,838 5,765 5,880 5,764
Depreciation and amortization...................... 3,426 3,019 4,389 6,084 5,886
Contract manufacturing............................. 3,612 5,002 2,617 1,115 72
Interest........................................... 284 428 735 940 1,205
Other.............................................. -- -- -- -- 850
-------- -------- -------- -------- --------
62,776 53,818 44,679 56,538 50,892
-------- -------- -------- -------- --------
Net loss............................................. $(23,070) $ (8,625) $(11,579) $(32,424) $(23,508)
======== ======== ======== ======== ========
Weighted average number of Class A and common stock
outstanding, basic and
diluted............................................ 31,308 30,992 28,702 24,464 19,768
======== ======== ======== ======== ========
Net loss per share, basic and diluted................ $ (0.74) $ (0.28) $ (0.40) $ (1.33) $ (1.19)
======== ======== ======== ======== ========
</TABLE>

<TABLE>
<CAPTION>
DECEMBER 31,
--------------------------------------------------------
1999 1998 1997 1996 1995
-------- -------- -------- -------- --------
(IN THOUSANDS)
<S> <C> <C> <C> <C> <C>
BALANCE SHEET DATA:
Cash, cash equivalents and marketable
securities......................................... $ 93,599 $113,530 $128,041 $ 97,028 $ 59,622
Working capital...................................... 59,725 83,499 88,953 72,960 36,254
Total assets......................................... 136,999 156,915 168,380 137,582 93,811
Capital lease obligations and note payable,
long-term portion.................................. 2,731 3,066 3,752 5,148 5,978
Shareholders' equity................................. 109,532 131,227 138,897 106,931 67,856
</TABLE>

<PAGE>

RISK FACTORS

You should carefully consider the following risk factors before you decide
to buy our common stock. If any of these risks actually occur, our business,
financial condition, operating results or cash flows could be materially
adversely affected. This could cause the trading price of our common stock to
decline and you may lose part or all of your investment.

RISKS RELATED TO OUR BUSINESS, INDUSTRY AND STRATEGY

MOST DRUG RESEARCH AND DEVELOPMENT PROGRAMS FAIL.

Only a small minority of all research and development programs ultimately
result in commercially successful drugs. It is not possible to predict whether
any program will succeed until it actually produces a drug that is commercially
marketed for a significant period of time. We are attempting to develop drugs
for human therapeutic uses and we cannot assure you that any of our research and
development activities will be successful or that any of our potential product
candidates will be commercialized. If our clinical trials are not successful, we
will not be able to develop and commercialize any of our products. The Phase III
trial of BDNF that Amgen-Regeneron Partners conducted during 1995 and 1996 for
ALS failed to achieve its expected results.

In order to obtain regulatory approvals for the commercial sale of our
product candidates, we will be required to complete extensive clinical trials in
humans to demonstrate the safety and efficacy of the products. While we seek to
broaden our product pipeline, as described below, we have limited experience in
conducting clinical trials in these new product areas.

A clinical trial may fail for a number of reasons, including:

o failure to enroll a sufficient number of patients meeting eligibility
criteria;

o failure of the product candidate to demonstrate safety or efficacy;

o the development of serious or life-threatening adverse events, for
example, side effects, caused by or connected with exposure to the
product candidate; and

o the failure of clinical investigators, trial monitors and other
consultants, or trial subjects to comply with trial plan or protocol.

THERE ARE RISKS INVOLVED IN EXPANDING OUR INITIAL FOCUS AND BROADENING OUR
PRODUCT PIPELINE.

Expanding from our initial focus on degenerative neurologic disease and
broadening our product pipeline to include drug candidates for the treatment of
other diseases involves risks. As we expand our focus to broaden our product
pipeline and as our scientific efforts lead us in new directions into conditions
or diseases outside of our areas of experience and expertise, we will require
additional internal expertise or external collaborations in areas in which we
currently do not have substantial resources and personnel. As we develop drug
candidates independently, we will require additional resources that may be
difficult to obtain. We may have to enter into collaboration arrangements with
others that may require us to relinquish rights to certain of our technologies,
product candidates or products that we would otherwise pursue independently. We
cannot assure you that we will be able to acquire the necessary expertise or
enter into collaboration agreements on acceptable terms to develop additional
drug candidates.

WE HAVE INCURRED SUBSTANTIAL LOSSES AND EXPECT TO INCUR LOSSES OVER THE NEXT
SEVERAL YEARS.

We have not received revenue from the commercialization of our product
candidates. We do not expect to receive any revenue from the commercialization
of our products for several years. We have incurred losses in each year since
inception of operations in 1988. As of December 31, 1999, we had an accumulated
deficit of $200.3 million. We do not know if we will ever have an approved
product or achieve significant revenues or profitable operations.

<PAGE>

WE MAY REQUIRE ADDITIONAL FINANCING, WHICH MAY BE DIFFICULT TO OBTAIN AND MAY
DILUTE YOUR OWNERSHIP INTEREST.

To date, we have received revenues from (1) our licensees and collaborators
for research and development efforts, (2) Merck and Sumitomo Pharmaceuticals for
contract manufacturing and (3) investment income. We cannot assure you that
these revenues will continue or to what extent our expenses will be reimbursed
by our licensees or collaborators. In the absence of revenues from the
commercialization of our product candidates or other sources (the amount,
timing, nature, or source of which we cannot predict), our losses will continue
as we conduct our research and development activities. Our activities may expand
over time and may require additional resources and our operating losses may be
substantial over at least the next several years. Our losses may fluctuate from
quarter to quarter and will depend, among other factors, on the timing of
certain expenses and on the progress of our research and development efforts.

We have had negative cash flow from operations in each year since our
inception. We expect that the funding requirements for our activities will
remain substantial and could increase significantly if, among other things, our
development or clinical trial programs are successful or our research is
expanded. In addition, we are required to provide capital from time to time to
fund and remain equal partners with Amgen in Amgen-Regeneron Partners. Our
aggregate capital contributions to Amgen-Regeneron Partners from the
partnership's inception in June 1993 through December 31, 1999 was
$51.1 million. We expect that our capital contributions in 2000 will total at
least $4.5 million. These contributions could increase or decrease, depending
upon, among other things, the nature and cost of ongoing and additional BDNF and
NT-3 studies that Amgen-Regeneron Partners may conduct and the outcomes of those
studies. In addition, the amount needed to fund our operations will also depend
on other factors, including:

o the potential future need to expand our professional and support staff
and facilities to support new areas of research and development;

o the success of our research and development programs;

o the status of patent and other intellectual property right developments;
and

o the extent and success of any collaborative research arrangements.

We anticipate the net proceeds from this offering, together with our cash,
cash equivalents and marketable securities of approximately $93.6 million, will
be sufficient for our working capital needs for several years. We have no
established banking arrangements through which we can obtain short-term
financing or a line of credit. We may seek additional funding through
collaborative arrangements and public or private financing. Additional financing
may not be available to us on acceptable terms or at all. If we raise additional
funds by issuing equity securities, including as a result of the exercise by
Procter & Gamble or Medtronic of their warrants, further dilution to our then
existing shareholders may result.

OUR SUCCESS DEPENDS UPON OBTAINING FDA AND FOREIGN REGULATORY APPROVAL TO MARKET
PRODUCTS CURRENTLY UNDER DEVELOPMENT.

The safety, effectiveness, testing, manufacture, distribution, labeling,
storage, record-keeping, approval, advertising and promotion of our product
candidates and the research and development activities associated with them are
subject to extensive federal, state and foreign regulation. If we fail to obtain
the necessary approvals or comply with regulatory requirements, or if any of our
approvals are restricted, suspended or revoked, there could be a material
adverse effect on us. Even if we are able to develop drugs and related therapies
that are approved for sale by the FDA or by foreign regulatory authorities, we
cannot assure you that any such drugs or related therapies will be commercially
successful.

The compounds we are developing will require significant additional
time-consuming and costly research and development, including further
preclinical and clinical testing, before we can file an application for
commercial approval. As an initial step in the FDA regulatory approval process,
preclinical studies are typically conducted in animals to identify potential
safety problems. The results of preclinical studies are submitted to the FDA as
a part of Investigation of New Drugs, or the IND, which is filed to comply with
FDA regulations before beginning human clinical studies. For several of our drug
candidates, no reliably predictive animal model exists. As a result, no
indication of efficacy for human beings is available until these product
candidates progress to human clinical trials.

<PAGE>

The submission of an IND, may not result in FDA authorization to commence
clinical trials. If clinical trials begin, we may not complete testing of any of
our product candidates within any specific time period, if at all. Our compounds
may prove to have undesirable and unintended toxic side effects that may
interrupt or delay clinical studies and could ultimately prevent or limit their
commercial use. The creation of antibodies against the therapeutic protein may
totally or partially neutralize the effectiveness of the protein or, in some
cases, can cross react with the patient's own proteins, resulting in an
"auto-immune type" disease. We or the regulatory authorities may suspend or
terminate clinical trials at any time if the people participating in such trials
are believed to be exposed to unacceptable health risks. Clinical trials, if
completed, may not show any potential product to be safe or effective. Thus, the
FDA and other regulatory authorities may not approve any of our product
candidates for any disease indication.

The extensive regulatory approval process required by the FDA and by
comparable agencies in other countries can take many years and requires the
expenditure of substantial resources. This gives larger companies with greater
financial resources a competitive advantage. Data obtained from preclinical and
clinical activities are subject to different interpretations which could delay,
limit, or prevent FDA regulatory approval. We may encounter delays or rejections
based upon changes in FDA policy for drug approval during the period of
development and FDA regulatory review. We may also encounter similar delays or
rejection of applications in foreign countries. We cannot assure you that even
after such time and expenditures, regulatory approval will be obtained for any
compounds we develop. Moreover, even if approval is granted, such approval may
have limitations on the indicated uses for which compounds may be marketed.
Subsequent discovery of previously unknown problems with a product or its
manufacturer may result in restrictions on the product or manufacturer,
including withdrawal of the product from the market.

WE FACE SUBSTANTIAL COMPETITION, WHICH MAY RESULT IN OTHERS DISCOVERING,
DEVELOPING OR COMMERCIALIZING PRODUCTS BEFORE OR MORE SUCCESSFULLY THAN WE DO.

There is substantial competition in the biotechnology and pharmaceutical
industries from pharmaceutical, biotechnology and chemical companies. Many of
our competitors have substantially greater research, preclinical and clinical
product development and manufacturing capabilities and financial, marketing and
human resources than we do. Our smaller competitors may also be significant if
they acquire or discover patentable inventions or form collaborative
arrangements or merge with large pharmaceutical companies. We also compete with
academic institutions, government agencies and other public and private research
organizations in the development of technologies and processes and, in some
instances, compete with others in acquiring technology from such institutions,
agencies and organizations. We cannot assure you that we will be able to produce
approved compounds that have commercial potential. Even if we achieve product
commercialization, one or more of our competitors may achieve product
commercialization earlier than we do or obtain patent protection that dominates
or adversely affects our activities.

There is substantial competition in the discovery and development of
treatments for obesity and obesity-related morbidities, including Type II
diabetes, as well as established and cost-effective and emerging prescription
and over-the-counter treatments for these conditions. For example, Amgen and a
number of other pharmaceutical companies are developing leptin and related
molecules. Clinical trials of leptin are currently under way. Many firms and
entities are engaged in research and development in the areas of cytokines,
interleukins, angiogenesis and muscle conditions. Some of these competitors are
currently conducting advanced preclinical and clinical research programs in
these areas. These and other competitors may have established substantial
intellectual property and other competitive advantages. The treatment of
constipating conditions is highly competitive, with a number of companies
providing over-the-counter remedies and other competitors attempting to discover
and develop improved over-the-counter or prescription treatments. Many
pharmaceutical and biotechnology companies are attempting to discover and
develop small-molecule based therapeutics, similar in at least certain respects
to our program with Procter & Gamble. In these and related areas, intellectual
property rights have been sought and certain rights have been granted to
competitors and potential competitors of ours and we may be at a substantial
competitive disadvantage in such areas as a result of, among other things, our
lack of experience, trained personnel and expertise. A number of corporate and
academic competitors are involved in the discovery and development of novel
therapeutics using tyrosine kinase receptors, orphan receptors and compounds
that are the focus of other research or development programs we are now
conducting. These competitors include Amgen and Genentech, as well as many
others.

<PAGE>

More specifically, our efforts to develop treatments for neurologic
diseases and conditions are being conducted in a highly competitive environment.
Even if BDNF is shown to be safe and effective to treat ALS or other conditions,
other companies have developed or are developing drugs for the treatment of the
same or similar conditions, including Rhone-Poulenc Rorer and Sanofi
Pharmaceuticals, Inc. Amgen is a direct competitor of ours in the field of
neurotrophic factors and possibly other fields. Other potential competitors
include Genentech and Cephalon, Inc., which is in a collaboration with Chiron
Corporation. Amgen, Genentech, Cephalon and others have filed patent
applications and obtained issued patents relating to neurotrophic factors, or
have announced that they are actively pursuing preclinical or clinical
development programs in the area of neurotrophic factors. Other companies have
developed or are developing drugs based on technology other than neurotrophic
factors for the treatment of diseases and injuries relating to the nervous
system (including ALS). We are also aware that several pharmaceutical companies
are conducting clinical trials in ALS with drugs that are orally administered.
Our developments relating to treatments for asthma or other inflammatory
conditions, obesity, diabetes and other conditions are subject to a similarly
competitive environment.

If a competitor announces a successful clinical study involving a product
that may be competitive with one of our product candidates or an approval by a
regulatory agency of the marketing of a competitive product, such announcement
may have a material adverse effect on our operations or future prospects or the
price of our common stock.

We also compete with academic institutions, governmental agencies and other
public or private research organizations which continue to conduct research,
seek patent protection and establish collaborative arrangements for the
development and marketing of products that would provide royalties for use of
their technology. These institutions are becoming more active in seeking patent
protection and licensing arrangements to collect royalties for use of the
technology that they have developed. Products developed in this manner may
compete directly with products we develop. We also compete with others in
acquiring technology from such institutions, agencies and organizations.

Our ability to compete will depend on how fast we can develop safe and
effective product candidates, complete clinical testing and approval processes
and supply commercial quantities of the product to the market. Competition among
product candidates approved for sale will also be based on efficacy, safety,
reliability, availability, price, patent position and other factors.

WE DEPEND ON THE COLLABORATIVE EFFORTS OF OUR ACADEMIC AND CORPORATE PARTNERS
FOR RESEARCH, DEVELOPMENT AND COMMERCIALIZATION OF SOME OF OUR PRODUCTS.

Our strategy for research, development and commercialization of some of our
products involves entering into various arrangements with academic and corporate
partners and others. As a result, our strategy depends, in part, upon the
success of these outside parties in performing their responsibilities. Our
collaborators may also be our competitors, such as Amgen. We cannot control the
amount and timing of resources that our collaborators devote to performing their
contractual obligations. We cannot assure you that these parties will perform
their obligations as expected or that any revenue will be derived from these
arrangements.

If our collaborators breach or terminate their agreement with us or
otherwise fail to conduct their collaborative activities in a timely manner, the
development or commercialization of the product candidate or research program
under such collaborative arrangement may be delayed. If that is the case, we may
be required to undertake unforeseen additional responsibilities or to devote
unforeseen additional funds or other resources to such development or
commercialization, or such development or commercialization could be terminated.
Our agreement with Procter & Gamble has an early termination provision whereby
either party has the right to terminate the agreement on June 30, 2002 by giving
the other party one year's notice on or before June 30, 2001. The termination or
cancellation of collaborative arrangements could adversely affect our financial
condition, intellectual property position and operations. In addition,
disagreements between collaborators and us could lead to delays in the
collaborative research, development, or commercialization of certain products or
could require or result in formal legal process or arbitration for resolution.
These consequences could be time-consuming and expensive and could have material
adverse effects on us.

Other than our contractual rights under our license agreements, we may be
limited in our ability to convince our licensees to fulfill their obligations.
If our licensees fail to act promptly and effectively, or if a

<PAGE>

dispute arises, it could have a material adverse effect on our results of
operations and the price of our common stock.

We rely upon scientific, technical and clinical data supplied by academic
and corporate collaborators, licensors, licensees, independent contractors and
others in the evaluation and development of potential therapeutic compounds. We
cannot assure you that there are no errors or omissions in this data that would
materially adversely affect the development of these compounds.

We may seek additional collaborative arrangements to develop and
commercialize our products in the future. We cannot assure you that we will be
able to negotiate acceptable collaborative arrangements in the future or that
they will be on favorable terms or that any collaborative arrangements will be
successful. In addition, our collaborative partners may pursue alternative
technologies or develop alternative compounds independently or in collaboration
with others as a means of developing treatments for the diseases targeted by
their collaborative programs with us.

THERE ARE RISKS RELATING TO PRODUCT MANUFACTURING.

Our ability to conduct timely preclinical and clinical research and
development programs, obtain regulatory approval, commercialize our product
candidates and fulfill our contract manufacturing obligations to others will
depend, in part, upon our ability to manufacture our products, either directly
or through third parties, in accordance with FDA and other regulatory
requirements.

If we are unable to manufacture our products, we would be unable to proceed
with or could experience delays in the regulatory process for our product
candidates under development, and experience delays in the commercialization of
our products. We cannot assure you that we will be able to manufacture products
successfully or in a cost-effective manner at our facilities. We may also have
difficulties obtaining the raw materials and supplies necessary to manufacture
our product candidates or the products we manufacture for others. If we are
unable to develop our own manufacturing facilities or to obtain or retain
third-party manufacturing on acceptable terms, we may not be able to conduct
certain future preclinical and clinical testing or to supply commercial
quantities of our product candidates. Our dependence upon third parties for the
manufacture of some of our products and related therapies may adversely
affect our profit margins and our ability to develop and deliver products on a
timely and competitive basis.

In addition, if our manufacturing facilities fail to comply with FDA and
other regulatory requirements, we will be required to suspend manufacturing.
This will have a material adverse effect on our financial condition, results of
operations and cash flow.

SINCE WE HAVE NO SALES AND MARKETING EXPERIENCE OR INFRASTRUCTURE, WE MAY HAVE
TO RELY ON THIRD PARTIES.

We have no sales, marketing and distribution experience or infrastructure.
We may have to rely significantly on sales, marketing and distribution
arrangements with third parties for the products we are developing. If in the
future we determine to perform sales, marketing and distribution functions
ourselves, we would face a number of additional risks, including:

o we may not be able to attract and build a significant marketing or sales
force;

o the cost of establishing a marketing or sales force may not be
justifiable in light of any product revenues; and

o our direct sales and marketing efforts may not be successful.

OUR PRODUCTS MAY NOT ACHIEVE COMMERCIAL SUCCESS.

The commercial success of any of our products will depend upon their
acceptance by patients, the medical community and third-party payors and on our
ability to successfully develop, manufacture and market our products. Among the
factors that we believe will materially affect acceptance of our products are:

o the timing of receipt of approvals for marketing our products and the
countries in which those approvals are obtained;

o the safety and efficacy of our products;

o the success of physician education programs;

<PAGE>

o the cost of our products in comparison with conventional or alternative
therapeutic products; and

o the availability of government and third-party payor reimbursement of our
products.

IF WE FAIL TO OBTAIN AN ADEQUATE LEVEL OF REIMBURSEMENT FOR OUR FUTURE PRODUCTS
BY THIRD-PARTY PAYORS, THERE MAY BE NO COMMERCIALLY VIABLE MARKETS FOR OUR
PRODUCTS.

The success of our products will depend, in part, upon the extent to which
a consumer will be willing to pay the price or be able to obtain reimbursement
for the cost of these products from government health administration
authorities, private health insurers and other organizations.

Significant uncertainties exist as to the reimbursement status of newly
approved therapeutic products. Medicare generally does not provide reimbursement
for self-administered prescription therapeutic agents. We cannot assure you that
(1) reimbursement in the United States or foreign countries will be available
for any of our products or (2) if available, there will be no decrease in the
future or (3) that reimbursement amounts will not reduce the demand for or the
price of our products. The unavailability or inadequacy of third-party
reimbursement for our products could have a material adverse effect on us.

Third-party payors are increasingly challenging the prices charged for
medical services and products and the trend towards managed care in the United
States and the growth of organizations such as health maintenance organizations,
which could control or significantly influence the purchase of health care
services and products, as well as legislative proposals to reform health care or
reduce government insurance programs, may result in lower prices for our
products. The cost containment measures that health care providers are
instituting and the effect of any health care reform could affect our ability to
sell our products and may have a material adverse effect on us. We are unable to
forecast what additional legislation or regulation, if any, relating to the
health care industry or third-party coverage and reimbursement may be enacted in
the future or what effect such legislation or regulation would have on our
business.

RISKS RELATED TO INTELLECTUAL PROPERTY

WE MAY NOT BE ABLE TO OBTAIN PATENT PROTECTION FOR OUR DISCOVERIES AND WE MAY
INFRINGE PATENT RIGHTS OF OTHERS.

We believe that patent protection of, and freedom to use, products or
processes that may result from our research and development efforts, our
licensors, licensees or collaborators is important to the possible
commercialization of our product candidates. We or our licensors or
collaborators have filed patent applications on products and processes relating
to AXOKINE, Cytokine Traps, Angiopoietins, BDNF and NT-3, as well as other
technologies and inventions in the United States and in certain foreign
countries. Although we have obtained a number of U.S. patents, we cannot assure
you that any additional patents will be issued. Moreover, we cannot assure you
that our products or processes will not be found to infringe the patents of
others or that any issued of our patents will provide adequate protection
against competitive products or otherwise be commercially valuable. Related to
patent issues, in March 1998, we and Amgen entered into an agreement not to sue
each other with respect to our activities relating to CNTF and AXOKINE. The
agreement also provides a simple mechanism for resolving our patent
interferences and related opposition and other patent proceedings relating to
CNTF and AXOKINE without protracted litigation. We also granted Amgen a license
to use CNTF and second generation CNTFs other than AXOKINE to treat retinal
degenerative conditions. We will not pay royalties or make other payments to
Amgen in consideration of this agreement.

In addition, patent law relating to the patentability and scope of claims
in the biotechnology field is evolving and our patent rights are subject to this
additional uncertainty. Others may independently develop similar products or
processes to those developed by us, duplicate any of our products or processes
or, if patents are issued to us, design around any products and processes
covered by our patents. We expect to continue to file products and process
patent applications with respect to our inventions. However, we cannot assure
you that we will file any such applications or, if filed, that the patents will
be issued. Patents issued to or licensed by us may be infringed by the products
or processes of others.

Defense and enforcement of our rights can be expensive and time consuming,
even if the outcome is favorable to us. It is possible that patents issued to or
licensed to us will be successfully challenged, that a court may find that we
are infringing validly issued patents of third parties, or that we may have to
alter our

<PAGE>

products or processes or pay licensing fees or cease certain activities to take
into account patent rights of third parties, causing additional unexpected costs
and delays which may have a material adverse effect on us.

IF WE ARE NOT ABLE TO KEEP OUR TRADE SECRETS CONFIDENTIAL, OUR TECHNOLOGY AND
INFORMATION MAY BE USED BY OTHERS TO COMPETE AGAINST US.

In addition to our reliance on patents, we attempt to protect our
proprietary products and processes by relying on trade secret laws and
nondisclosure and confidentiality agreements and exclusive licensing
arrangements with our employees and certain other persons who have access to our
proprietary products or processes or have licensing or research arrangements
exclusive to us. Despite these protections, no assurance can be given that these
agreements or arrangements will provide meaningful protection for our trade
secrets in the event of unauthorized use or disclosure of such information or
that others will not independently develop or obtain access to such products or
processes or that our competitive position will not be adversely affected
thereby. No assurance can be given that others will not independently develop
substantially equivalent proprietary information and techniques or otherwise
gain access to our trade secrets or technology or that we can meaningfully
protect our rights to our trade secrets.

WE MAY BECOME INVOLVED IN EXPENSIVE PATENT LITIGATION OR OTHER INTELLECTUAL
PROPERTY PROCEEDINGS WHICH COULD RESULT IN LIABILITY FOR DAMAGES OR STOP OUR
PRODUCT DEVELOPMENT AND COMMERCIALIZATION EFFORTS.

There has been substantial litigation and other proceedings regarding the
complex patent and other intellectual property rights in the pharmaceutical and
biotechnology industries. In addition to the patent interference proceeding
described above, we may become a party to patent litigation or other proceedings
regarding intellectual property rights.

Other types of situations in which we may become involved in patent
litigation or other intellectual property proceedings include:

o we may initiate litigation or other proceedings against third parties to
enforce our patent rights;

o we may initiate litigation or other proceedings against third parties to
seek to invalidate the patents held by these third parties or to obtain a
judgment that our products or services do not infringe the third parties'
patents;

o if our competitors file patent applications that claim technology also
claimed by us, we may participate in interference or opposition
proceedings to determine the priority of invention; and

o if third parties initiate litigation claiming that our processes or
products infringe their patent or other intellectual property rights, we
will need to defend against such claims.

The cost to us of any patent litigation or other proceedings, even if
resolved in our favor, could be substantial. Some of our competitors may be able
to sustain the cost of such litigation or proceedings more effectively than we
can because of their substantially greater financial resources. If a patent
litigation or other intellectual property proceeding is resolved unfavorably to
us, we may be enjoined from manufacturing or selling our products and services
without a license from the other party and be held liable for significant
damages. We may not be able to obtain any required license on commercially
acceptable terms or not at all.

Uncertainties resulting from the litigation and continuation of patent
litigation or other proceedings could have a material adverse effect on our
ability to compete in the marketplace. Patent litigation and other proceedings
may also absorb significant management time.

IF WE BREACH ANY OF THE AGREEMENTS UNDER WHICH WE LICENSE TECHNOLOGY FROM
OTHERS, WE COULD LOSE LICENSE RIGHTS THAT ARE IMPORTANT TO OUR BUSINESS.

We are a party to technology licenses that are important to our business
and expect to enter into additional licenses in the future. These licenses
impose commercialization, sublicensing, royalty, insurance and other obligations
on us. If we fail to comply with these requirements, the licensor will have the
right to terminate the license.

<PAGE>

RISKS RELATING TO ONGOING OPERATIONS

RECRUITING AND RETAINING QUALIFIED SCIENTIFIC AND MANAGEMENT PERSONNEL TO
PERFORM RESEARCH AND DEVELOPMENT WORK AND TO COMMERCIALIZE PRODUCTS IS CRITICAL
TO OUR SUCCESS.

Although we believe we have been successful in attracting and retaining
skilled and experienced scientific and management personnel, we cannot assure
you that we will be able to continue to attract and retain such personnel on
acceptable terms. The loss of any of our key personnel, in particular (1) our
Chairman, P. Roy Vagelos, M.D., (2) our President and Chief Executive Officer,
Leonard S. Schleifer, M.D., Ph.D. and (3) our Chief Scientific Officer, George
D. Yancopoulos, M.D., Ph.D., may have an adverse effect on us. In addition, our
anticipated growth and expansion into new areas requiring additional expertise
are expected to place increased demands on our resources and require the
recruitment of additional management personnel and the development of additional
expertise by existing management personnel. The failure to acquire such services
or to develop such expertise could have a material adverse effect on us.

WE COULD BE EXPOSED TO SIGNIFICANT LIABILITY CLAIMS IF WE ARE UNABLE TO OBTAIN
INSURANCE AT ACCEPTABLE COSTS OR OTHERWISE TO PROTECT US AGAINST POTENTIAL
PRODUCT LIABILITY CLAIMS.

The testing, manufacturing and marketing of human pharmaceutical products
entail significant inherent risks. Their use in clinical trials and their sale
may expose us to liability claims. These claims might be made directly by
consumers or by pharmaceutical companies or others selling the products. We are
insured by health care product liability insurance policies, including a policy
carried by Amgen-Regeneron Partners, the purpose of which is to cover certain
claims that could arise during the clinical trials of BDNF and NT-3. Such
coverage or the amount and scope of any coverage obtained in the future may be
inadequate to protect Regeneron in the event of a successful liability claim and
we cannot assure you that the amount of such insurance can be purchased,
increased or renewed. We cannot assure you that we will avoid a significant
product liability claim or recall that could have a material adverse effect on
us.

RISKS RELATING TO OUR COMMON STOCK

OUR STOCK PRICE COULD BE VOLATILE, WHICH COULD CAUSE YOU TO LOSE PART OR ALL OF
YOUR INVESTMENT.

There has been a history of significant volatility in the market price of
shares of biotechnology companies, including our shares and it is likely that
the market price of our common stock will continue to be highly volatile. In
1998, the bid price for our common stock fluctuated from a low of $5.75 a share
to $11.00 a share. In 1999, the bid price fluctuated from a low of $5.38 per
share to a high of $13.00 per share. From January 1, 2000 to March 8, 2000, the
bid price fluctuated from a low of $11.50 per share to a high of $56.44 per
share. The following factors may have a significant effect on the market price
of our common stock:

o fluctuations in our operating results,

o clinical trial results,

o announcements of technological innovations or new commercial therapeutic
products introduced by us or our competitors,

o governmental regulation,

o regulatory delays,

o litigation,

o developments in patent or other proprietary rights,

o public concern as to the safety or other implications of the drugs sought
to be developed by us or the genetic engineering involved in their
production, and

o general market conditions.

<PAGE>

OUR EXISTING SHAREHOLDERS MAY BE ABLE TO INFLUENCE THE OUTCOME OF CORPORATE
ACTIONS.

Holders of Class A stock (the shareholders who purchased their stock from
us before our initial public offering) are entitled to ten votes per share and
holders of common stock are entitled to one vote per share. Upon completion of
this offering, holders of Class A stock will hold 7.7% of our outstanding common
and Class A stock, or common shares, and 45.3% of the combined voting power of
the common shares and, if acting together, will be in position to significantly
influence the election of our directors and to effect or prevent certain
corporate transactions which require majority or supermajority approval of the
combined classes, including mergers and other business combinations. Upon the
completion of this offering:

o our current officers and directors will own 10.4% of our outstanding
common shares and 40.2% of the combined voting power of our common
shares;

o Procter & Gamble will hold 14.1% of our outstanding common shares and
8.4% of the combined voting power of our common shares; and

o Amgen will hold 13.5% of our outstanding common shares and 8.0% of the
combined voting power of our common shares.

WE HAVE ANTITAKEOVER DEFENSES THAT COULD DELAY OR PREVENT AN ACQUISITION AND
COULD ADVERSELY AFFECT THE PRICE OF OUR COMMON STOCK.

New York corporate law and our amended and restated certificate of
incorporation and by-laws contain provisions that could have the effect of
delaying or preventing a change in control of our company or our management that
shareholders may consider favorable or beneficial. These provisions could
discourage proxy contests and make it more difficult for you and other
shareholders to elect directors and take other corporate actions. These
provisions could also limit the price that investors might be willing to pay in
the future for shares of our common stock. These provisions include:

o authorization to issue "blank check" preferred stock, which is preferred
stock that can be created and issued by the board of directors without
prior shareholder approval, with rights senior to our common
stockholders; and

o a staggered board of directors, so that it would take three successive
annual meetings to replace all directors.

In addition, we have a shareholders rights plan which will make it more
difficult for a third party to acquire us without the support of our board of
directors and principal shareholders.

A SIGNIFICANT NUMBER OF OUR SHARES ARE ELIGIBLE FOR RESALE. THIS COULD REDUCE
OUR SHARE PRICE AND IMPAIR OUR ABILITY TO RAISE FUNDS IN NEW SHARE OFFERINGS.

Immediately after completion of this offering, we will have 36,430,516
shares of Class A and common stock outstanding and available for resale
beginning at various points of time in the future. In addition, we will have
5,856,222 outstanding stock options, including 333,000 stock options subject to
shareholder approval, and 1,557,400 warrants held by Procter & Gamble and
Medtronic as of March 8, 2000. Sales of substantial amounts of shares of our
common stock in the public market after this offering, or the perception that
those sales will occur, could cause the market price of our common stock to
decline. Those sales also might make it more difficult for us to sell equity and
equity-related securities in the future at a time and at a price that we
consider appropriate.

YOU WILL SUFFER IMMEDIATE AND SUBSTANTIAL DILUTION.

The price you will pay for our common stock in this offering will be
substantially higher than the $7.56 pro forma net tangible book value per share
of our outstanding Class A and common stock as of December 31, 1999. As a
result, you will experience immediate dilution of $34.19 in net tangible book
value per share, and our current shareholders will experience an immediate
increase in the net tangible book value per share of their shares of Class A and
common stock of $4.07.

<PAGE>

THIS PROSPECTUS CONTAINS FORWARD-LOOKING STATEMENTS

This prospectus and the documents incorporated by reference include
forward-looking statements. We have based these forward-looking statements on
our current expectations and projections about future events. These
forward-looking statements include, among other things, statements relating to:

o our anticipated business strategies,

o our anticipated clinical trials,

o our intention to introduce new products candidates,

o anticipated trends in our businesses,

o future capital expenditures, and

o our ability to conduct clinical trials and obtain regulatory approval.

The forward-looking statements included in this prospectus or in the
documents incorporated by reference are subject to risks, uncertainties and
assumptions about us. Our actual results of operations may differ materially
from the forward-looking statements as a result of, among other things, the
success or failure of our clinical trials, the speed at which our clinical
trials progress, the success of our competitors in developing products equal or
superior to ours, the success of our collaborative relationships and the other
reasons described under "Risk Factors." We undertake no obligation to publicly
update or revise any forward-looking statement, whether as a result of new
information, future events or otherwise. In light of these risks, uncertainties
and assumptions, the forward-looking events discussed in this prospectus might
not occur.

For these statements, we claim the protection of the safe harbor for
forward-looking statements contained in Section 21E of the Securities Act. Our
actual results could differ materially from those anticipated in these
forward-looking statements as a result of various factors, including all of the
risks discussed in "Risk Factors" and elsewhere in this prospectus.

USE OF PROCEEDS

We estimate that the net proceeds we will receive from the sale of
4,000,000 shares of our common stock will be approximately $158,100,000 at an
assumed public offering price of $41.75 per share, after deducting underwriting
discounts and commissions and the estimated expenses of this offering. We will
not receive any proceeds from the sale of shares of our common stock by our
selling shareholder, Amgen Inc., if the underwriters exercise their
over-allotment option.

We intend to use these net proceeds for working capital and general
corporate purposes, including:

o All of the costs to fund preclinical and clinical development of product
candidates that are being developed independent of any corporate partner,
such as AXOKINE and Cytokine Traps;

o Our share of the costs to fund preclinical and clinical development of
product candidates that have been partnered, such as BDNF, NT-3, VEGF
Trap and Angiopoietins;

o Basic research;

o Commercialization expenses;

o Purchase of equipment and expansion of manufacturing facilities; and

o Potential acquisitions of companies and technologies which complement our
business. No such transactions are planned or being negotiated as of the
date of this prospectus.

Pending application of the net proceeds as described above, we intend to
invest the net proceeds of this offering primarily in U.S. Government and other
investment grade obligations, interest bearing money market funds and other
financial instruments. See "Investment Company Act Considerations."

DIVIDEND POLICY

We have never paid cash dividends and do not anticipate paying any in the
foreseeable future. In addition, under the terms of certain of our debt
agreements, we are not permitted to declare or pay cash dividends.

<PAGE>

CAPITALIZATION

The following table sets forth our capitalization as of December 31, 1999
and as adjusted to give effect to our sale of 4,000,000 shares of our common
stock in this offering, after deducting underwriting discounts and commissions
and estimated expenses of this offering and the application of the estimated net
proceeds. See "Use of Proceeds."

<TABLE>
<CAPTION>
AT DECEMBER 31, 1999
------------------------
ACTUAL AS ADJUSTED
--------- -----------
(IN THOUSANDS, EXCEPT
SHARE DATA)
<S> <C> <C>
Cash, cash equivalents and marketable securities........................................ $ 93,599 $ 251,699
========= =========
Capital lease obligations--long-term portion............................................ 1,204 1,204
--------- ---------
Note payable--long-term portion......................................................... 1,527 1,527
--------- ---------
Shareholders' equity:
Preferred stock, $.01 par value; 30,000,000 shares authorized; issued and
outstanding--none.................................................................. -- --
Class A stock, $.001 par value; 40,000,000 shares authorized, 3,605,133 shares issued
and outstanding--actual and as adjusted............................................ 4 4
Common stock, $.001 par value; 60,000,000 shares authorized; 27,817,636 shares issued
and outstanding--actual; 31,817,636 shares issued and outstanding--as adjusted..... 28 32
Additional paid-in capital............................................................ 310,296 468,392
Accumulated deficit................................................................... (200,303) (200,303)
Accumulated other comprehensive loss.................................................. (493) (493)
--------- ---------
Total shareholders' equity......................................................... 109,532 267,632
--------- ---------
Total capitalization............................................................... $ 112,263 $ 270,363
========= =========
</TABLE>

<PAGE>

DILUTION

As of December 31, 1999, our net tangible book value before the offering
was $109.5 million or $3.49 per common share. "Net tangible book value per
share" is determined by dividing our net tangible book value (total assets less
total liabilities) by the number of common shares outstanding. After giving
effect to the sale of the shares of our common stock in this offering and after
deducting underwriting discounts and commissions and the estimated expenses of
this offering, our pro forma net tangible book value as of December 31, 1999
would have been $267.6 million in the aggregate, or $7.56 per common share. This
represents an immediate increase in net tangible book value of $4.07 per common
share to existing holders and immediate dilution of $34.19 per common share to
new investors purchasing shares of common stock in this offering. The following
table illustrates this per share dilution:

<TABLE>
<S> <C> <C>
Assumed public offering price............................................... $41.75
Net tangible book value per common share before this offering............. $3.49
Increase attributable to new investors.................................... 4.07
-----
Pro forma net tangible book value per common share after this offering...... 7.56
------
Dilution to new investors................................................... $34.19
------
------
</TABLE>

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

"Dilution" means the difference between the public offering price per share of
common stock and the pro forma net tangible book value per common share after
giving effect to this offering.

<PAGE>

SELECTED FINANCIAL DATA

We have derived the selected financial data presented below for the years
ended December 31, 1999, 1998 and 1997 and at December 31, 1999 and 1998 from
our audited financial statements and notes thereto included in our Annual Report
on Form 10-K for the year ended December 31, 1999 which is incorporated by
reference in this prospectus. We have derived the selected financial data for
the years ended December 31, 1996 and 1995 and at December 31, 1997, 1996 and
1995 from our audited financial statements and notes thereto not included in
this prospectus. You should read the selected financial data together with the
audited financial statements and the section entitled "Management's Discussion
and Analysis of Financial Condition and Results of Operations" in our Annual
Report which is incorporated by reference in this prospectus.

<TABLE>
<CAPTION>
YEAR ENDED DECEMBER 31,
--------------------------------------------------------
1999 1998 1997 1996 1995
-------- -------- -------- -------- --------
(IN THOUSANDS, EXCEPT PER SHARE DATA)
<S> <C> <C> <C> <C> <C>
STATEMENT OF OPERATIONS DATA:
Revenues
Contract research and development.................. $ 24,539 $ 19,714 $ 17,400 $ 17,303 $ 23,247
Research progress payments......................... -- 9,500 5,000 -- --
Contract manufacturing............................. 9,960 9,113 4,458 2,451 1,140
Investment income.................................. 5,207 6,866 6,242 4,360 2,997
-------- -------- -------- -------- --------
39,706 45,193 33,100 24,114 27,384
-------- -------- -------- -------- --------
Expenses
Research and development........................... 44,940 37,047 27,770 28,269 23,310
Loss in Amgen-Regeneron Partners................... 4,159 2,484 3,403 14,250 13,805
General and administrative......................... 6,355 5,838 5,765 5,880 5,764
Depreciation and amortization...................... 3,426 3,019 4,389 6,084 5,886
Contract manufacturing............................. 3,612 5,002 2,617 1,115 72
Interest........................................... 284 428 735 940 1,205
Other.............................................. -- -- -- -- 850
-------- -------- -------- -------- --------
62,776 53,818 44,679 56,538 50,892
-------- -------- -------- -------- --------
Net loss............................................. $(23,070) $ (8,625) $(11,579) $(32,424) $(23,508)
======== ======== ======== ======== ========
Weighted average number of Class A and common stock
outstanding, basic and diluted .................... 31,308 30,992 28,702 24,464 19,768
======== ======== ======== ======== ========
Net loss per share, basic and diluted................ $ (0.74) $ (0.28) $ (0.40) $ (1.33) $ (1.19)
======== ======== ======== ======== ========
</TABLE>

<TABLE>
<CAPTION>
DECEMBER 31,
--------------------------------------------------------
1999 1998 1997 1996 1995
-------- -------- -------- -------- --------
(IN THOUSANDS)
<S> <C> <C> <C> <C> <C>
BALANCE SHEET DATA:
Cash, cash equivalents and marketable securities .... $ 93,599 $113,530 $128,041 $ 97,028 $ 59,622
Working capital...................................... 59,725 83,499 88,953 72,960 36,254
Total assets......................................... 136,999 156,915 168,380 137,582 93,811
Capital lease obligations and note payable,
long-term portion.................................. 2,731 3,066 3,752 5,148 5,978
Shareholders' equity................................. 109,532 131,227 138,897 106,931 67,856
</TABLE>

<PAGE>

BUSINESS

GENERAL

o AXOKINE(R) SECOND GENERATION CILIARY NEUROTROPHIC FACTOR: Acts on the
brain region regulating food intake and energy expenditure. AXOKINE is
being developed for the treatment of obesity and complications of obesity
such as Type II diabetes, and is in clinical trials. We are also
developing a modified form of AXOKINE (pegylated) that in preclinical
studies is substantially longer acting than unmodified AXOKINE. This may
allow less frequent and lower dosing in patients.

o CYTOKINE TRAPS: Protein-based antagonists for cytokines such as
interleukin-1 (called IL-1), interleukin-4 (IL-4), and interleukin-6
(IL-6) and a single antagonist that blocks both IL-4 and interleukin-13
(IL-13). These cytokines are thought to play a major role in diseases
such as rheumatoid arthritis and other inflammatory diseases, asthma,
allergic disorders and cancer. Cytokine Traps are potential treatments
for these diseases, and at least one Cytokine Trap is expected to enter
clinical trials by 2001.

o ANGIOPOIETINS: A new family of growth factors, discovered by us, that are
specific for blood vessels and early hemopoietic stem cells. The
Angiopoietins, and engineered forms of these growth factors that can act
as activators and blockers, are in preclinical testing for promoting
blood vessel growth (to provide blood flow in diseased hearts and other
tissues that have lost their original blood supplies), for blocking blood
vessel growth (for the treatment of cancers), for fixing leaky blood
vessels (that cause swelling and edema in diseases such as stroke,
diabetic retinopathy and inflammatory diseases) and for promoting the
growth and mobilization of certain hemopoietic cells such as stem cells
and platelets.

o BRAIN-DERIVED NEUROTROPHIC FACTOR, OR BDNF: Promotes survival of the
spinal cord neurons that die in amyotrophic lateral sclerosis (or ALS,
commonly known as Lou Gehrig's Disease) in pre-clinical models. BDNF is
in clinical trials for ALS using two routes of administration; one of
these trials is based on the results of a prior phase III clinical trial.

<PAGE>

TECHNOLOGY PLATFORMS

Targeted Genomics and Bioinformatics. In contrast to basic genomics
approaches, which attempt to identify every gene in a cell or genome, we use
Targeted Genomics approaches to identify specific genes likely to be of
therapeutic interest. Such approaches include homology cloning using
low-stringency hybridization approaches, homology cloning using degenerate
oligonucleotides in polymerase chain reaction-based amplification searches,
subtractive hybridization approaches and bioinformatics-based algorithms that
search public genomic and expressed sequence tag (EST) databases for genes of
interest. These approaches have resulted in the discovery of a wide variety of
important genes useful for developing drugs in a diverse number of therapeutic
areas, including angiogenesis, cancer, muscle disorders, bone and cartilage
formation, fibrosis and inflammatory diseases. A particular focus of these
efforts is the identification of so-called orphan receptors, as described in the
next section.

Functionomics: Orphan Receptor Technology and Functional Cloning of Growth
Factors for these Orphan Receptors. The therapeutic utility of many growth
factors depends, in part, on the exquisite specificity of their actions. This
specificity is determined largely by the limited distribution of receptors for
these factors on the target cells of interest. Using proprietary technology
initially developed for the discovery and characterization of neurotrophic
factors and their receptors described in the previous section on Targeted
Genomics and Bioinformatics, we have discovered new receptor proteins
specifically expressed on particular cell populations of potentially important
clinical interest. These cell populations include not only additional subsets of
neurons but non-neuronal cells, such as the endothelial cells that constitute
blood vessels, skeletal muscle cells, cartilage cells and hemopoietic cells.
Because these novel receptor proteins initially have no defined growth factor
partner, they are termed orphan receptors. We have also obtained licenses and
established collaborations for additional orphan receptors, including licenses
from The Salk Institute for Biological Studies. Our scientists then define the
growth factor-binding portion of the orphan receptors and engineer it into an
antibody-like reagent, termed a receptor-body. This receptor-body is used to
detect a source of the unknown growth factor and a cDNA library is produced from
this source. The millions of cDNAs in this library are then introduced into
millions of mammalian cells and the rare cell that has taken up the cDNA
encoding the unknown growth factor is detected using the receptor-body. The cell
is then isolated and its cDNA amplified, allowing for the molecular cloning of
the unknown growth factor. These approaches have allowed our scientists to clone
growth factor families such as the Angiopoietins and Ephrins.

Designer Protein Therapeutics and Genetic Engineering. In cases in which
the natural gene product is itself not a product candidate, we utilize our
Designer Protein Therapeutics platform approaches to genetically engineer
product candidates with the desired properties. These technologies allow us to
develop derivatives of the growth factors and their receptors, which can allow
for modified agonistic or antagonistic properties that may prove to be
therapeutically useful. Examples include the generation of AXOKINE as a second
generation version of CNTF and the development of Cytokine Traps and the VEGF
Trap. Traps are derivatives of the receptors for cytokines and VEGF, in which
the binding portions of two different receptor components are combined to form a
very high-affinity antagonist. These Traps are comprised of fully human
sequences which, in preclinical studies, display useful therapeutic properties
such as prolonged half-life in the circulation. This technology platform has
already produced more than 10 patented proteins, several of which are in
preclinical development.

Additional research and development capabilities. These capabilities
include molecular and cellular biology, protein chemistry, transgenics and gene
knockouts, disease modeling, viral gene delivery of proteins, recombinant
expression of proteins and large-scale manufacturing of recombinant proteins.

22
<PAGE>

OUR PROGRAMS
SELECTED PRODUCTS AND PROGRAMS

<TABLE>
<CAPTION>
TECHNOLOGY PLATFORMS USED
FOR DISCOVERY AND
DEVELOPMENT PROGRAM AND PRODUCT TARGETED INDICATION STAGE COMMERCIALIZATION RIGHTS
- ------------------------- ------------------------- -------------------- ------------ -------------------------
<S> <C> <C> <C> <C>
TARGETED GENOMICS AXOKINE(R) Second Obesity and Clinical Regeneron
DESIGNER PROTEIN Generation Ciliary complications of
THERAPEUTICS Neurotrophic Factor obesity such as Type
II diabetes

TARGETED GENOMICS NT-3 (Neurotrophin-3) Constipating Clinical Regeneron and Amgen
conditions
associated with
spinal cord injury
and other medical
conditions

CYTOKINE TRAPS
--------------

DESIGNER PROTEIN IL-1 Rheumatoid arthritis Preclinical Regeneron
THERAPEUTICS and other
inflammatory
disorders

DESIGNER PROTEIN IL-4 Asthma and allergic Preclinical Regeneron
THERAPEUTICS disorders

DESIGNER PROTEIN IL-4/13 Asthma and allergic Preclinical Regeneron
THERAPEUTICS disorders

DESIGNER PROTEIN IL-2, IL-3, IL-5, IL-6, Multiple Research Regeneron
THERAPEUTICS IL-15, gamma-interferon,
TGF-beta and others

ANGIOGENESIS
------------

DESIGNER PROTEIN VEGF Trap Cancer Preclinical Regeneron and
THERAPEUTICS Procter & Gamble

TARGETED GENOMICS Angiopoietin-1 Ischemia, vascular Preclinical Regeneron and
FUNCTIONOMICS leak, edema and Procter & Gamble
DESIGNER PROTEIN hemopoiesis
THERAPEUTICS

TARGETED GENOMICS Ephrins, Angiopoietin-2 Cancer, ischemia and Research Regeneron and
FUNCTIONOMICS hemopoiesis Procter & Gamble
DESIGNER PROTEIN
THERAPEUTICS

TARGETED GENOMICS MUSCLE DISEASES AND Muscle atrophy and Research Regeneron and
FUNCTIONOMICS DISORDERS injury Procter & Gamble
-------------------

BONE AND CARTILAGE
------------------

TARGETED GENOMICS RORs Osteoarthritis Research Regeneron and
FUNCTIONOMICS Procter & Gamble

TARGETED GENOMICS DDRs Fibrosis and Research Regeneron and
FUNCTIONOMICS cirrhosis Procter & Gamble

TARGETED GENOMICS G-PROTEIN COUPLED Multiple targets Research Regeneron and
FUNCTIONOMICS RECEPTORS Procter & Gamble
-----------------
</TABLE>

23
<PAGE>

AXOKINE. AXOKINE is our patented second generation ciliary neurotrophic
factor, called CNTF. In an earlier clinical program, CNTF was evaluated as a
potential treatment for patients with ALS. It was discovered that reduced
appetite and weight loss were among the prominent adverse events in these
patients. Later preclinical studies with AXOKINE in animal models of obesity
confirmed the ability of AXOKINE to induce substantial weight loss,
preferentially of fat as opposed to lean body mass. AXOKINE is effective in all
obesity models studied to date, which include diet induced obesity and genetic
obesity rodent models (db/db and ob/ob mice) and causes marked weight loss in
lean animals.

AXOKINE has similarities to and important differences from leptin, a
protein that is secreted by fat cells which another company is currently
evaluating in clinical trials in obese people. AXOKINE and leptin use similar
intracellular signaling pathways but signal through different, but closely
related, receptors; they interact with the CNTF and the leptin receptor,
respectively. AXOKINE causes weight loss comparable to leptin in ob/ob mice;
ob/ob mice are genetically obese mice which lack leptin but have the intact
leptin receptor. Leptin in pharmacological doses does not induce weight loss in
mice made obese with high fat/high calorie diet. In contrast, AXOKINE in this
model produces a 30% weight loss in three weeks without causing obvious signs of
toxicity.

The vast majority of obese humans have intact leptin receptors and
increased serum leptin levels. Hence, human obesity does not appear to be a
leptin deficient state but, rather, a condition of leptin resistance. Based on
the animal studies, AXOKINE is anticipated to be pharmacologically active in
patients with obesity, despite their elevated leptin levels and leptin
resistance.

Obesity is a major health problem in all developed countries. The
prevalence of obesity in the United States has increased substantially during
the past decade. According to the 1997 National Task Force on the Prevention and
Treatment of Obesity, one in three American adults is now considered overweight.
A 1998 National Institutes of Health report confirmed that obesity significantly
increases a number of health risks, including Type II diabetes. Type II diabetes
is estimated to affect more than 15 million people in the United States, with 80
to 90 percent of these people having obesity as a contributing factor to their
diabetes. Obesity-related conditions such as stroke and myocardial infarct are
estimated to contribute to 300,000 deaths yearly, ranking second only to smoking
as a cause of preventable death. Expenses and loss of income caused by obesity
have been estimated to reach $68 billion annually. Current treatment of obesity
consists of diet, exercise and other lifestyle changes, and a limited number of
drugs. The fact that the population overall is rapidly becoming more obese
testifies to the fact that treatment of obesity is difficult and characterized
by very high recidivism.

We are developing AXOKINE for the treatment of obesity and complications of
obesity such as non-insulin dependent diabetes mellitus (also known as NIDDM or
adult onset diabetes or Type II diabetes). We expect to start a Phase II
clinical trial in March of 2000 to test the safety and efficacy of AXOKINE in
severely obese patients.

In the first quarter of 1999, we commenced a Phase I clinical study with
Procter & Gamble to determine the safety of AXOKINE administered subcutaneously
for a short duration to mildly to moderately obese healthy volunteers. In
September 1999, we summarized preliminary interim results of the Phase I safety
study. Patients received increasing doses of AXOKINE (or placebo) administered
subcutaneously in both single and multiple dose regimens. The single dose study
demonstrated that AXOKINE is well tolerated at low doses. At higher single
doses, nausea, vomiting, and herpes cold sores were observed. Increased cold
sores caused by herpes simplex virus, or HSV, were also reported in previous
clinical studies of CNTF, AXOKINE's parent molecule. As of the date of our
summary of interim results, the multiple dose study (daily administration for 14
days) had been conducted at doses that were well tolerated in the single dose
part of the study. Nine patients and four placebo patients had been completed
with no reports of nausea, cough, or herpes cold sores. The treated patients
lost weight and had decreased food (caloric) intake compared with those on
placebo. One patient in the multiple low dose group, who was HSV-positive prior
to treatment and had been previously diagnosed with Bell's palsy, had a
recurrence of Bell's palsy approximately two weeks after the patient's last
administration of AXOKINE.

After examining the interim data from the Phase I study (including the
possibility that the market for AXOKINE might be limited to HSV-negative
patients) as part of an internal review of drug development programs and
budgets, Procter & Gamble decided to return to us the product rights to AXOKINE.
We and Procter &

<PAGE>

Gamble completed the Phase I study in HSV-negative patients. Under certain
circumstances, Procter & Gamble will continue to be entitled to receive a small
royalty on any sales of AXOKINE.

At completion, the multiple dose study included a total of 27 patients at
four doses that were generally well tolerated in the single-dose part of the
study. Overall, the treated patients lost weight and had decreased food
(caloric) intake compared to those on placebo. At doses up to 2 mcg/kg/day in
patients, some of whom were HSV-positive and some of whom were HSV-negative, and
at doses above 2 mcg/k/day in patients, all of whom were HSV-negative, there
were no reports of vomiting or herpes cold sores. Some patients in the study
experienced a reversible and generally asymptomatic increase in pulse rate in a
dose-related fashion. One patient in the 1 mcg/kg/day group who had been
previously diagnosed with Bell's palsy had a recurrence of Bell's palsy
approximately two weeks after the patient's last administration of AXOKINE. It
is not known whether AXOKINE had any role in this patient's recurrence of Bell's
palsy, and the patient recovered. Bell's palsy is a potentially permanently
disfiguring condition but most often resolves spontaneously within weeks. Many
researchers believe that Bell's palsy may be caused by HSV.

Based on the results of the Phase I study, we expect to start in March 2000
a double-blind, placebo-controlled Phase II dose-ranging trial to study the
safety and efficacy of AXOKINE in severely obese patients. The study will be
conducted in approximately 175 obese patients at six centers with patients
treated for 90 days at doses up to 2 mcg/kg/day, i.e., doses that were not
associated with herpes cold sores in the Phase I trial. There will be no
restriction as to a subject's prior history of herpes cold sores. The Phase II
study is designed to confirm the weight loss observed in the Phase I trial and
determine the lowest effective well-tolerated dose. We also plan to collect
additional data in the study about the relationship of AXOKINE and reactivation
of HSV, about the effect of AXOKINE on pulse rate, and about the possible
development of neutralizing antibodies when AXOKINE is administered for a longer
time.

We are also developing a modified form of AXOKINE (pegylated) that in
preclinical studies is substantially longer acting than unmodified AXOKINE. This
may allow less frequent and lower dosing in patients.

We have recently signed an agreement with Emisphere Technologies, Inc. to
establish a research and development collaboration to utilize Emisphere's oral
drug delivery technology for AXOKINE. In preliminary preclinical pharmacokinetic
studies, the Emisphere technology was able to achieve measurable blood levels of
AXOKINE.

Cytokine Traps. Our widely-cited research on the CNTF class of
neurotrophic factors led to the discovery that CNTF, although it is a
neurotrophic factor, belongs to the "superfamily" of factors referred to as
cytokines. Cytokines are soluble proteins secreted by the cells of the body. In
many cases, cytokines act as messengers to help regulate immune and inflammatory
responses. In excess, cytokines can be harmful and have been linked to a variety
of diseases. This cytokine superfamily includes factors such as erythropoietin,
thrombopoietin, granulocyte-colony stimulating factor and the interleukins (or
ILs). Our research has led to proprietary insights into the receptors and signal
transduction mechanisms used by the entire cytokine superfamily and to novel
approaches to develop both agonists and antagonists for a variety of cytokines.
Our scientists have created protein-based antagonists for IL-1, IL-4, IL-6 and a
single antagonist that blocks both IL-4 and IL-13. These antagonists are more
potent than previously described antagonists, allowing lower levels of these
antagonists to be used; moreover, these antagonists are comprised entirely of
natural human-derived sequences and thus would not be expected to induce an
immune reaction in humans (although no assurance can be given since none have
yet been tested in humans). These cytokine antagonists are termed Cytokine
Traps. Because pathological levels of IL-1, IL-4, IL-6 and IL-13 seem to
contribute to a variety of disease states, these Cytokine Traps have the
potential to be important therapeutic agents. Our Cytokine Traps soak up excess
cytokines, blocking their harmful effects. Blocking cytokines and growth factors
is a proven therapeutic approach with a number of drugs already approved or in
clinical development.

In animal models, our IL-1 trap blocks the activity of IL-1. IL-1 is a
principal mediator of joint inflammation characteristic of rheumatoid arthritis
and is thought to be responsible for cartilage and bone damage close to the
joint. Over two million people (1% of the U.S. population) are estimated to have
rheumatoid arthritis; of these, 10% eventually become disabled. A recently
reported study by another company suggested that blocking IL-1 may be an
effective therapeutic strategy to treat rheumatoid arthritis.

<PAGE>

Our IL-1 trap is expected to be 1000 times more potent than this molecule, based
upon preclinical studies. Antagonists for IL-4 and IL-13 may be therapeutically
useful in an assortment of allergy and asthma-related disease situations in
which IL-4 and IL-13 are thought to play a contributory role and in a variety of
vaccination settings in which blocking IL-4 and IL-13 may help elicit more of
the desired type of immune response to the vaccine. We have developed both an
IL-4 trap and an IL-4/13 trap which is a single molecule that can block both
interleukin-4 and interleukin-13. IL-6 has been implicated in the pathology and
progression of multiple myeloma, certain solid tumors, AIDS, lymphomas (both
AIDS-related and non-AIDS-related), osteoporosis, and other conditions. We plan
to commence a clinical trial of at least one of our Cytokine Traps this year.

Our research regarding protein-based cytokine antagonists currently
includes molecular and cellular research to improve or modify our Cytokine Trap
technology, process development efforts to produce experimental and clinical
research quantities of the Cytokine Traps and in vivo and in vitro studies to
further understand and demonstrate the efficacy of the Cytokine Traps. We also
have patents covering additional Cytokine Traps for IL-2, IL-3, IL-5, IL-15,
gamma-interferon, transforming growth factor beta, and others, which are being
pursued at the research level.

BDNF. Brain-derived neurotrophic factor is a naturally occurring human
protein. During 1995 and 1996, Amgen conducted, on behalf of Amgen-Regeneron
Partners, a Phase III BDNF clinical trial to treat ALS. This study involved
1,135 patients, with each patient scheduled to receive subcutaneous treatment
for nine months. ALS is a disease that attacks motor neurons, those nerve cells
that cause muscles to contract. Degeneration of these neurons causes muscle
weakness, leading to death due to respiratory insufficiency. ALS afflicts adults
primarily between the ages of 40 and 70 years old; average survival is three to
five years following diagnosis. It is estimated that approximately 25,000 people
in the United States have ALS. In January 1997, we and Amgen announced that the
Phase III study failed to demonstrate clinical efficacy. Although that trial
failed to achieve its predetermined end points, subsequent analyses indicated
that a retrospectively-defined subset of ALS patients in the trial may have
received a survival benefit from BDNF treatment.

BDNF is currently being developed by Amgen-Regeneron Partners for potential
use in treating ALS through two routes of administration: intrathecal (infusion
into the spinal fluid through an implanted pump, supplied by Medtronic) and
subcutaneous (injection under the skin). In the fourth quarter of 1998, Amgen,
on behalf of the partnership, began an intrathecal study in more than 200
patients with ALS. Subcutaneous studies conducted by us on behalf of the
partnership began in the first quarter of 1998. The subcutaneous studies are
based on retrospective analysis of the data from the Phase III trial of BDNF
that was completed in 1996, as described earlier. A double-blind, placebo-
controlled, multi-center study of more than 300 ALS patients who will receive
BDNF subcutaneously began in August 1999. We and Sumitomo Pharmaceuticals are
collaborating in the development of BDNF in Japan, initially for the treatment
of ALS.

NT-3. Amgen-Regeneron Partners' clinical development of NT-3 is currently
focused on constipating conditions. In 1998, we, on behalf of Amgen-Regeneron
Partners, completed a small clinical study that included healthy volunteers and
patients suffering from severe idiopathic constipation, and began additional
exploratory studies that are continuing in 2000 in patients who suffer from
constipation associated with conditions such as spinal cord injury and the use
of narcotic analgesics. In February 2000, we initiated a double-blind,
placebo-controlled Phase II study in more than 100 patients with functional
constipation. We and Amgen are developing NT-3 in the United States under a
license from Takeda Chemical Industries, Ltd.

Angiogenesis and Hemopoiesis. A plentiful blood supply is required to
nourish every tissue and organ of the body. Diseases such as diabetes and
atherosclerosis wreak their havoc, in part, by destroying blood vessels
(arteries, veins and capillaries) and compromising blood flow. Decreases in
blood flow (known as ischemia) can result in non-healing skin ulcers and
gangrene, painful limbs that cannot tolerate exercise, loss of vision and heart
attacks. In other cases, disease processes can damage blood vessels by breaking
down vessel walls, resulting in defective and leaky vessels. Leaking vessels can
lead to swelling and edema, as occurs in brain tumors, following ischemic
stroke, in diabetic retinopathy and in arthritis and other

<PAGE>

inflammatory diseases. Finally, some disease processes such as tumor growth
depend on the induction of new blood vessels.

Depending on the clinical situation, positively or negatively regulating
blood vessel growth could have important therapeutic benefits, as could the
repair of damaged and leaky vessels. Thus, building new vessels, by a process
known as angiogenesis, can improve circulation to ischemic limbs and heart, aid
in healing of skin ulcers or other chronic wounds and in establishing tissue
grafts. Reciprocally, blocking tumor-induced angiogenesis can blunt tumor
growth. In addition, repairing leaky vessels can reverse swelling and edema.

Vascular endothelial growth factor (VEGF) was the first growth factor shown
to be specific for blood vessels, by virtue of having its receptor specifically
expressed on blood vessel cells. Our scientists have used their Targeted
Genomics and Functionomics technology platforms to discover a second family of
angiogenic growth factors, termed the Angiopoietins, and received patents for
the members of this family. The Angiopoietins include naturally occurring
positive and negative regulators of angiogenesis, as described in numerous
scientific manuscripts published by our scientists and their collaborators.

To discover the Angiopoietins, our scientists exploited their platform
technologies. They first used Targeted Genomics approaches to identify a new
family of growth factor receptor proteins expressed on blood vessels. These
proteins were termed orphan receptors because their putative ligands had not yet
been identified. Our scientists then used functional expression cloning
technologies (Functionomics) to discover the growth factors for these orphan
receptors, which they termed the Angiopoietins. Finally, they and their
collaborators performed an assortment of functional studies to define the
biologic roles of the Angiopoietins and their potential applications in disease
processes.

These studies have revealed that VEGF and the Angiopoietins normally
function in a coordinated and collaborative manner during blood vessel growth.
Thus, the growth of new blood vessels to nourish ischemic tissue seemingly
requires use of both these agents. In addition, Angiopoietin-1 seems to play a
critical role in stabilizing the vessel wall, and the use of this growth factor
has the ability to prevent or repair leaky vessels. In terms of blocking vessel
growth, both VEGF and Angiopoietin manipulation seem to be of value. Currently,
we have a highly potent VEGF antagonist, termed the VEGF-Trap, in preclinical
development as an anti-angiogenic agent for cancer. In addition, we have
Angiopoietin-1 and engineered designer versions in preclinical studies aimed at
evaluating its utility for blocking blood vessel leak, and for growing blood
vessels in ischemia. Finally, as part of our collaboration with Procter &
Gamble, we are developing animal models and high-throughput screens and
conducting medicinal chemistry efforts to develop small molecule regulators of
angiogenesis.

Hemopoietic stem cells and blood vessel cells share a common precursor,
termed the hemangioblast. The receptors for the Angiopoietins are thus also
expressed on hemopoietic lineage cells. The Angiopoietins are in preclinical
studies for their abilities to promote growth and mobilization of hemopoietic
stem cells and megakaryocytes.

We and others have identified a family of growth factors termed the Ephrins
and their receptors termed the Ephs. Members of this family have specific roles
in angiogenesis and hemopoiesis, which are being pursued in preclinical studies.

This work in angiogenesis and hemopoiesis is being conducted in
collaboration with scientists at Procter & Gamble as part of our agreement.

Muscle Atrophy and Related Disorders. Muscle atrophy occurs in many
neuromuscular diseases and also when muscle is unused, as often occurs during
prolonged hospital stays and during convalescence. Currently, physicians have
few options to prescribe for patients with muscle atrophy or other muscle
conditions which afflict millions of patients globally. Thus, a factor that
might have beneficial effects on skeletal muscle could have significant clinical
benefit. The muscle program is currently focused on conducting in vivo and in
vitro experiments with the objective of demonstrating and further understanding
the molecular mechanisms involved in muscle atrophy. This work is being
conducted in collaboration with scientists at Procter & Gamble as part of our
agreement.

<PAGE>

Other Early Stage Programs: Cartilage Growth Factor Receptor System and
Osteoarthritis, Collagen Receptors and Fibrosis, and G-Protein Coupled
Receptors. Osteoarthritis results from the wearing down of the articular
cartilage surfaces that cover joints. Thus, growth factors that specifically act
on cartilage cells could have utility in osteoarthritis. Using our platform
technologies that utilize Targeted Genomics to discover orphan receptors,
together with our functional biology capabilities, our scientists have
discovered a growth factor receptor system selectively expressed by cartilage
cells, termed Regeneron Orphan Receptor 2 (ROR2). Furthermore, our scientists
have demonstrated that this growth factor receptor system is required for normal
cartilage development in mice as revealed by gene knockout technology. In
addition, together with collaborators, our scientists have proven that mutations
in this growth factor receptor system cause inherited defects in cartilage
development in humans. Thus, this growth factor receptor system is an exciting
new target for cartilage diseases such as osteoarthritis.

Fibrotic diseases, such as cirrhosis, result from the excess production of
fibrous extracellular matrix by certain cell types that are inappropriately
activated in these diseases. We and our collaborators identified orphan
receptors, termed Discoidin Domain Receptors 1 and 2 (DDR1 and DDR2), that are
expressed by the activated cell types in fibrotic disease. We have further shown
that these receptors bind and are activated by the fibrous matrix they produce.
Thus, these receptors are important new targets in fibrotic disease.

We also have an intensive program to discover and characterize G-Protein
Coupled Receptors, which have historically been among the most useful targets
for pharmaceuticals.

The work in these programs is being conducted in collaboration with
scientists at Procter & Gamble as part of our agreement.

COLLABORATIVE RELATIONSHIPS

We currently conduct programs in collaboration with academic and corporate
partners and independently. We have entered into research collaboration and
licensing agreements with various corporate partners, including Procter &
Gamble, Amgen and Sumitomo Pharmaceuticals.

Procter & Gamble. The majority of our scientific resources are devoted to
our collaborative activities with Procter & Gamble in the fields of
angiogenesis, cancer, bone growth and related areas, muscle injury and atrophy
and small molecule (orally active) drugs.

In May 1997, we entered into a ten-year collaboration agreement with
Procter & Gamble to discover, develop and commercialize pharmaceutical products.
Procter & Gamble agreed over the first five years of the various agreements to
purchase up to $60.0 million in our equity, of which, as of December 31, 1999,
it had purchased $42.9 million. In addition, Procter & Gamble purchased $10.0
million of our common stock in 1997. Procter & Gamble agreed over the first five
years of the various agreements to provide up to $94.7 million in support of our
research efforts related to the collaboration, of which we had received $24.0
million as of December 31, 1999.

In September 1997, our ten-year agreement with Procter & Gamble was
expanded to include AXOKINE and related molecules, and we agreed to develop
AXOKINE initially to treat obesity associated with Type II diabetes. In the
first quarter of 1999, we and Procter & Gamble commenced a Phase I clinical
study to determine the safety of AXOKINE administered subcutaneously for a short
duration to mildly to moderately obese healthy volunteers. After examining the
interim data from the Phase I study (including the possibility that the market
for AXOKINE might be limited to herpes simplex virus (commonly called
HSV)-negative patients) as part of an internal review of drug development
programs and budgets, Procter & Gamble decided to return to us the product
rights to AXOKINE. We and Procter & Gamble completed the Phase I study in
HSV-negative patients. Based on the final results of the Phase I study, we
expect to start in March 2000 a double-blind, placebo-controlled Phase II
dose-ranging trial to study the safety and efficacy of AXOKINE in severely obese
patients. Under certain circumstances, Procter & Gamble will continue to be
entitled to receive a small royalty on any sales of AXOKINE. Procter & Gamble's
decision to return to us product rights to AXOKINE has no impact on our broader
relationship with Procter & Gamble.

Under our agreement with Procter & Gamble, any drugs that may result from
the collaboration will be jointly developed and marketed, with the parties
equally sharing development costs and profits. In addition,

<PAGE>

during the second five years of the Procter & Gamble Agreement, the companies
will share all collaboration costs equally. Either party may terminate
collaborative research after five years, subject to reversion of certain rights
to us. We contributed our technologies and intellectual property relating to a
broad set of our programs and activities, as well as future research programs
and activities, to the collaboration. Excluded from the collaboration with
Procter & Gamble are our neurotrophic factor and cytokine research programs. Our
neurotrophic factor programs will continue to be developed in collaboration with
Amgen and Sumitomo Pharmaceuticals. Our cytokine research programs will continue
to be developed independently. In addition to the potential development of
protein-based therapeutics, the collaboration will seek to discover and develop
small molecule, orally active therapeutics useful in the treatment of muscle
diseases and conditions.

Amgen. We and Amgen are conducting clinical trials of BDNF and NT-3 on
behalf of Amgen-Regeneron Partners, a general partnership owned equally by us
and Amgen. We are required to fund 50% of the development costs of
Amgen-Regeneron Partners to maintain 50% of the commercialization rights.
Assuming equal capital contributions to Amgen-Regeneron Partners, we and Amgen
share any profits or losses of Amgen-Regeneron Partners equally. BDNF is
currently being developed by Amgen-Regeneron Partners for potential use in
treating ALS through two routes of administration: intrathecal (infusion into
the spinal fluid through an implanted pump, supplied by Medtronic, Inc.) and
subcutaneous (injection under the skin). The Amgen-Regeneron Partners Phase III
trial of BDNF for ALS, completed in 1996, failed to achieve its predetermined
end points, but subsequent analyses indicated that a retrospectively defined
subset of ALS patients in the trial may have received a survival benefit from
BDNF treatment.

Under our agreement with Amgen, following preclinical development, we will
attempt to develop with Amgen and, if such effort is successful, commercialize,
market, and distribute BDNF and NT-3 drug products in the United States through
Amgen-Regeneron Partners.

The development and commercialization of BDNF and NT-3 outside of the
United States, Japan, China, and certain other Pacific Rim countries will be
conducted solely by Amgen through a license from us and, with respect to NT-3,
from Takeda (under a license agreement between Amgen-Regeneron, Genentech, Inc.,
and Takeda). In return, we will receive royalty payments based on Amgen's net
sales of any products in the licensed territory. In the licensed territory,
Amgen is solely responsible for funding clinical development and related costs
of the licensed products, as well as costs of their commercial exploitation, and
will have sole discretion with respect to all such development, manufacturing,
and marketing of the products and sole responsibility for filing applications
for regulatory approvals.

Sumitomo. In connection with a $4.4 million equity investment made by
Sumitomo Chemical Company, Ltd. in March 1989, we granted Sumitomo Chemical a
limited right of first negotiation to license up to three of the product
candidates we decide to commercialize in Japan on financial and commercial terms
as we may offer. We are obligated periodically to inform and, if requested, to
meet with Sumitomo Chemical management about our progress in research and
development.

Our collaborative agreement in June 1994 with Sumitomo Pharmaceuticals, an
affiliate of Sumitomo Chemical, to develop BDNF in Japan, was the first of such
license agreements. Under the terms of the agreement, Sumitomo Pharmaceuticals
agreed to pay up to $40.0 million to us, including $25.0 million in research
payments (all of which we have received) and up to $15.0 million in progress
payments payable upon achievement of certain development milestones, of which
$5.0 million was received (reduced by $0.5 million of Japanese withholding tax)
in August 1998 in connection with Sumitomo's initiating a Phase I safety study
of BDNF in Japan. In addition, Sumitomo Pharmaceuticals agreed to reimburse us
for our activities in developing manufacturing processes for BDNF and supplying
BDNF and other research materials to Sumitomo Pharmaceuticals. The agreement may
be terminated by Sumitomo Pharmaceuticals at its discretion; such termination
would result in the reversion to us of all rights to BDNF in Japan.

Medarex. We recently entered into a collaboration under a binding
memorandum of understanding with Medarex, Inc. to discover, develop and
commercialize human antibodies as therapeutics. We will contribute our expertise
in discovering and characterizing proteins as drug targets, and Medarex will
contribute its HuMab-Mouse(TM) technology to create fully human antibody
products for those targets. Together we have selected more than twenty initial
targets, including growth factors, cytokines, and receptors, and plan to add
additional targets in the future. We and Medarex intend to prioritize targets
based upon a variety of criteria, including target validation, reagent
availability, market opportunity, competitive factors, intellectual property

<PAGE>

position, and the expected feasibility of obtaining antibodies that have the
desired properties. The HuMAb-Mouse is a transgenic mouse whose genes for
creating mouse antibodies have been inactivated and replaced by human antibody
genes. This makes it possible to rapidly create and develop fully human
antibodies as drug candidates. We and Medarex agreed to share preclinical and
clinical responsibilities and intend to jointly market any drugs that result
from this collaboration.

Emisphere. We have also recently signed an agreement with Emisphere
Technologies, Inc. to establish a research and development collaboration to
utilize Emisphere's oral drug delivery technology for AXOKINE. In preliminary
preclinical pharmacokinetic studies, the Emisphere technology was able to
achieve measurable blood levels of AXOKINE. Under the terms of the agreement, we
will support research at Emisphere and under certain conditions will make
additional payments, including license and milestone payments. We will receive
exclusive worldwide commercialization rights to oral products that result from
the collaboration and pay Emisphere a royalty on sales of any such products.

Other Agreements. We have agreements with individual researchers and
universities to conduct sponsored research and development programs. The goal of
these agreements is to extend our capabilities and to acquire proprietary rights
to the results of sponsored research. We are a party to a number of sponsored
research agreements which include grants to us of exclusive licenses to certain
discoveries and technologies developed at, among other places, the Max Planck
Institute and the University of California at San Francisco. We have also
collaborated with Glaxo Wellcome plc to discover and develop small
molecule-based treatments for neurodegenerative diseases. In addition to these
sponsored research agreements, we (individually or in partnership with our
collaborators) provide resource material and information that relate to its
product candidates and research programs to over 400 investigators at private
and public institutions throughout the world. We provide supplies, materials and
know-how to these investigators on a confidential basis in exchange for access
to additional research and ownership of certain proprietary rights resulting
from the work of the investigators.

MANUFACTURING

We maintain a manufacturing facility in Tarrytown, New York. This facility,
which was designed to comply with FDA current good manufacturing practices
(called GMP), produces preclinical and clinical supplies of our products and
product candidates.

In 1993, we purchased our Rensselaer, New York manufacturing facility,
which is being used to manufacture products for Sumitomo Pharmaceuticals and
Merck under contracts with them. We may use the facility to produce other
product candidates and materials in the future.

PATENTS, TRADEMARKS AND TRADE SECRETS

Our success depends, in part, on our ability to obtain patents, maintain
trade secret protection and operate without infringing on the proprietary rights
of third parties. Our policy is to file patent applications to protect
technology, inventions and improvements that are considered important to the
development of our business. We have been granted 42 U.S. patents and we have
more than 100 pending applications. We are the exclusive or nonexclusive
licensee of a number of additional U.S. patents and patent applications. We also
rely upon trade secrets, know-how and continuing technological innovation to
develop and maintain its competitive position. We or our licensors or
collaborators have filed patent applications on products and processes relating
to neurotrophic factors and other technologies and inventions in the United
States and in certain foreign countries. We intend to file additional patent
applications, when appropriate, relating to improvements in these technologies
and other specific products and processes. We plan to aggressively prosecute,
enforce and defend our patents and other proprietary technology.

EMPLOYEES

As of December 31, 1999, we had 437 full-time employees, 82 of whom hold a
Ph.D. or M.D. degree or both. We believe that we have been successful in
attracting skilled and experienced personnel in a highly competitive
environment.

<PAGE>

MANAGEMENT

DIRECTORS AND EXECUTIVE OFFICERS

The following table provides information with respect to our directors and
executive officers as of February 29, 2000:

<TABLE>
<CAPTION>
NAME AGE POSITION
- ------------------------------------------------ --- ------------------------------------------------
<S> <C> <C>
P. Roy Vagelos, M.D............................. 70 Chairman of the Board of Directors (Class II)
Leonard S. Schleifer, M.D., Ph.D................ 47 Director (Class I), President, Chief Executive
Officer and Founder
Charles A. Baker................................ 67 Director (Class III)
Michael S. Brown, M.D........................... 59 Director (Class III) and Member of Scientific
Advisory Board
Alfred G. Gilman, M.D., Ph.D.................... 58 Director (Class II), Member of Scientific
Advisory Board and Co-Founder
Joseph L. Goldstein, M.D........................ 60 Director (Class II) and Member of Scientific
Advisory Board
Fred A. Middleton............................... 50 Director (Class I)
Eric M. Shooter, Ph.D........................... 76 Director (Class I) and Chairman of Scientific
Advisory Board
George L. Sing.................................. 51 Director (Class III)
George D. Yancopoulos, M.D., Ph.D............... 40 Senior Vice President, Research and Chief
Scientific Officer
Jesse M. Cedarbaum, M.D......................... 48 Vice President, Clinical Affairs
Murray A. Goldberg.............................. 55 Vice President, Finance & Administration, Chief
Financial Officer, Treasurer and Assistant
Secretary
Hans-Peter Guler, M.D........................... 51 Vice President, Clinical Sciences
Stephen L. Holst................................ 58 Vice President, Quality Assurance and Regulatory
Affairs
Richard X. Horne................................ 49 Staff Vice President, Human Resources
William G. Roberts, M.D......................... 42 Vice President, Regulatory Development
Randall G. Rupp, Ph.D........................... 53 Vice President, Manufacturing and Process
Science
Joseph M. Sorrentino, Ph.D...................... 48 Vice President, Intellectual Property
Neil Stahl, Ph.D................................ 43 Vice President, Preclinical Development and
Biomolecular Science
David M. Valenzuela, Ph.D....................... 49 Vice President, Genomics and Bioinformatics
Douglas S. McCorkle............................. 43 Controller and Assistant Treasurer
Beverly C. Dubs................................. 45 Administrative Controller and Assistant
Treasurer
</TABLE>

The Board of Directors is divided into three classes, denominated Class I,
Class II and Class III, with members of each class holding office for staggered
three-year terms. Our Scientific Advisory Board consists of individuals with
recognized expertise in neurobiology, clinical neurology, molecular biology and
related fields who advise us about present and long-term scientific planning,
research and development.

P. Roy Vagelos, M.D., 70, has been chairman of the board of our company and
a member of the Scientific Advisory Board since January 1995. He became a
part-time employee of Regeneron in January 1999. Prior to joining Regeneron,
Dr. Vagelos was Chairman of the Board and Chief Executive Officer of

<PAGE>

Merck & Co., Inc. He joined Merck in 1975, became a director in 1984, President
and Chief Executive Officer in 1985 and Chairman in 1986. Dr. Vagelos retired
from all positions with Merck in 1994. He is also currently a member of the
Board of Directors of PepsiCo, Inc., The Prudential Insurance Company of America
and Estee Lauder Companies.

Leonard S. Schleifer, M.D., Ph.D., 47, founded our company in 1988 and has
been its president and chief executive officer since its inception and served as
Chairman of the Board from 1990 through 1994. In 1992, Dr. Schleifer was
appointed Clinical Professor of Neurology at the Cornell University Medical
School and from 1984 to 1988 he was Assistant Professor at the Cornell
University Medical School in the Departments of Neurology and Neurobiology.
Dr. Schleifer received his M.D. and Ph.D. in Pharmacology from the University of
Virginia. Dr. Schleifer is a licensed physician and is certified in Neurology by
the American Board of Psychiatry and Neurology.

Charles A. Baker, 67, has been a director of our company since February
1989. Since December 1989, he has been the Chairman, President and Chief
Executive Officer of The Liposome Company, Inc., a publicly held company. During
his career, Mr. Baker served in senior management capacities in various
pharmaceutical companies, including the positions of Group Vice President,
Squibb Corporation (now Bristol-Myers Squibb) and President, Squibb
International. He also held various senior executive positions at Abbott
Laboratories and Pfizer, Inc. Mr. Baker is a special limited partner in
Sanderling Ventures, which is a shareholder of the Company.

Michael S. Brown, M.D., 59, has been a director of our company since June
1991 and a member of our Scientific Advisory Board since January 1988.
Dr. Brown is Professor of Medicine and Genetics and the Director of the Center
for Genetic Diseases at The University of Texas Southwestern Medical Center at
Dallas. He is a member of the National Academy of Sciences. He is a Director of
Pfizer, Inc. His scientific contributions in cholesterol and lipid metabolism
were made in collaboration with Dr. Joseph L. Goldstein. Dr. Brown and
Dr. Goldstein jointly received the Nobel Prize for Physiology or Medicine in
1985.

Alfred G. Gilman, M.D., Ph.D., 58, a co-founder of our company, has been a
director of our company since July 1990 and a member of our Scientific Advisory
Board since 1988. Dr. Gilman has been the Raymond and Ellen Willie Professor of
Molecular Neuropharmacology and Chairman of the Department of Pharmacology at
The University of Texas Southwestern Medical Center at Dallas since 1981 and was
named a Regental Professor in 1995. Dr. Gilman is a member of the National
Academy of Sciences. He is the Consulting Editor of "Goodman and Gilman's The
Pharmacological Basis of Therapeutics," the leading medical pharmacology
textbook. Dr. Gilman received the Nobel Prize for Physiology or Medicine in
1994. Dr. Gilman is a member of the Board of Directors of Eli Lilly & Company.

Joseph L. Goldstein, M.D., 60, has been a director of our company since
June 1991 and a member of our Scientific Advisory Board since January 1988.
Dr. Goldstein has been the Professor of Medicine and Genetics and Chairman of
the Department of Molecular Genetics at The University of Texas Southwestern
Medical Center at Dallas for more than five years. Dr. Goldstein is a member of
the National Academy of Sciences. Dr. Goldstein and Dr. Brown jointly received
the Nobel Prize for Physiology or Medicine in 1985.

Fred A. Middleton, 50, has been a director of our company since July 1990.
Mr. Middleton is a General Partner of Sanderling Ventures, a venture capital
firm he co-founded with Dr. Robert McNeil in December 1987 specializing in early
stage biomedical companies. Sanderling Ventures is a shareholder of the Company.
Between 1984 and 1987, he was Managing General Partner of Morgan Stanley
Ventures and, from 1978 through 1984, was Vice President and Chief Financial
Officer of Genentech, Inc. and President, Genentech Development Corporation.

Eric M. Shooter, Ph.D., 76, a co-founder of our company, has been a
director of our company and chairman of the Scientific Advisory Board since
1988. Dr. Shooter has been a Professor at Stanford University School of Medicine
since 1968. He was the founding Chairman of the Department of Neurobiology at
Stanford University School of Medicine in 1975 and served as its Chairman until
1987. He is a Fellow of the Royal Society of England, a Fellow of the American
Academy of Arts and Sciences and a Foreign Associate of the Institute of
Medicine of the National Academy of Sciences.

<PAGE>

George L. Sing, 51, has been a director of our company since January 1988.
From February 1990 until February 14, 1991, Mr. Sing served as a consultant to
Merrill Lynch Venture Capital Inc. with respect to the Company. From 1982 to
February 1990, Mr. Sing was a Vice President and member of the Board of
Directors of Merrill Lynch Venture Capital Inc., a venture capital firm. Since
1993, Mr. Sing has been a general partner of Zitan Partners, an investment and
advisory firm.

George D. Yancopoulos, M.D., Ph.D., 40, has been senior vice president,
Research since June 1997 and chief scientific officer since January 1998. Dr.
Yancopoulos was Vice President, Discovery from January 1992 until June 1997 and
was employed by us since March 1989 as Senior Staff Scientist and Head of
Discovery from January 1991 to January 1992. He received his Ph.D. in
Biochemistry and Molecular Biophysics and his M.D. from Columbia University. In
a 1997 survey by the Institute for Scientific Information, he was listed among
the 11 most highly cited scientists and was the only non-academic scientist in
that group.

Jesse M. Cedarbaum, M.D., 48, has been our vice president, Clinical Affairs
since January 1993 and was Program Director of Clinical Affairs of the Company
from July 1990 until December 1992. He was Associate Professor of Neurology and
Neuroscience at Cornell University Medical College and director of the Parkinson
and Movement Disorders Clinics, New York Hospital and The Burke Rehabilitation
Center from 1983 to 1990 and is currently Clinical Associate Professor of
Neurology at Mt. Sinai Medical School in New York. Dr. Cedarbaum is a board
certified neurologist. Dr. Cedarbaum received his M.D. from the Yale University
School of Medicine.

Murray A. Goldberg, 55, has been our vice president, Finance and
Administration, Treasurer and Chief Financial Officer since March 1995 and
Assistant Secretary since January 2000. Prior to joining us, Mr. Goldberg was
Vice President, Finance, Treasurer and Chief Financial Officer of PharmaGenics,
Inc. from February 1991 and a Director of that company from May 1991. From 1987
to 1990, Mr. Goldberg was Managing Director, Structured Finance Group at the
Chase Manhattan Bank, N.A. and from 1973 to 1987 he served in various managerial
positions in finance and corporate development at American Cyanamid Company.

Hans-Peter Guler, M.D., 51, has been our vice president, Clinical Sciences
since April 1998. From 1994 until joining the Company, Dr. Guler was employed by
Chiron Corporation, most recently as Senior Director of Clinical Development.
From 1989 to 1994, he was Associate Director of Drug Development in the
Pharmaceuticals Divisions of CIBA-GEIGY Corporation. Dr. Guler received his M.D.
from the University of Zurich.

Steven L. Holst, 58, has been our vice president, Quality Assurance and
Regulatory Affairs since October 1997. From 1993 until October 1997, Mr. Holst
was employed by Novo Nordisk A/S, most recently as Senior Regulatory Officer and
Responsible Head of its worldwide Health Care group. From 1990 to 1993, he was
Director of our Regulatory Affairs and Quality Assurance Groups.

Richard X. Horne, 49, has been our Staff Vice President, Human Resources
since August 1998. Immediately prior to joining Regeneron, he was Vice
President, Human Resources at Braintree Hospital in Braintree, MA, serving in
that capacity since 1990. Mr. Horne also was a member of the Board of Directors
of The Rehabilitation Hospital of Rhode Island from October 1997 until April
1998.

William Roberts, M.D., 42, has been our vice president, Regulatory
Development since May 1999. From 1993 until joining us, Dr. Roberts was employed
by Merck & Co., Inc., as Associate Director, Gastroenterology Clinical Research
and subsequently, Director, Regulatory Affairs. He received his M.D. from the
Columbia University College of Physicians & Surgeons.

Randall G. Rupp, Ph.D., 53, has been our vice president, Manufacturing and
Process Science since January 1992 and was our director of manufacturing from
July 1991 until December 1992. He received his Ph.D. in Biomedical Sciences from
the University of Texas, M.D. Anderson Hospital and Tumor Institution, Houston.

Joseph M. Sorrentino, Ph.D., 48, has been our vice president, Intellectual
Property since September 1999. Immediately before joining us, he was Vice
President and Counsel (Biotechnology Patents) at

<PAGE>

Bristol-Myers Squibb Co., which he joined in 1990. Dr. Sorrentino received his
Ph.D. in Biochemistry from the University of Texas and his J.D. from the
University of Arizona.

Neil Stahl, Ph.D., 43, has been our vice president, Preclinical Development
and Biomolecular Sciences since January 2000. He joined us in 1991. Before
becoming Vice President, Biomolecular Sciences in July 1997, Dr. Stahl was
Director, Cytokines and Signal Transduction. Dr. Stahl received his Ph.D. in
Biochemistry from Brandeis University.

David Valenzuela, Ph.D., 49, has been our vice president, Genomics and
Bioinformatics since January 1998. Dr. Valenzuela joined us in 1990. He received
his Ph.D. in Molecular Biology from the Albert Einstein College of Medicine,
Yeshiva University.

Douglas S. McCorkle, 43, has been our controller since May 1998 and
Assistant Treasurer since June 1998. Before joining us, Mr. McCorkle was the
Controller at Intergen Company from January 1997. He was a manager from 1995 to
1996, Senior Associate from 1992 to 1995 and Associate from 1990 to 1991, with
PricewaterhouseCoopers LLP.

Beverly C. Dubs, 45, has been our administrative controller since May 1998
and Assistant Treasurer since August 1990. Ms. Dubs has served in various
finance and administration capacities at Regeneron since 1989.

INVESTMENT COMPANY ACT CONSIDERATIONS

The Investment Company Act of 1940, as amended, requires the registration
of, and imposes various substantive restrictions on, certain companies that
engage primarily, or propose to engage primarily, in the business of investing,
reinvesting or trading in securities, or fail certain statistical tests
regarding the composition of assets and sources of income and are not primarily
engaged in businesses other than investing, holding, owning, or trading
securities. We presently satisfy these statistical tests and intend to remain
primarily engaged in businesses other than investing, reinvesting, owning,
holding, or trading securities. In addition, we are relying on an SEC position
that biotechnology companies such as our company are not investment companies
required to register under the 1940 Act. We will seek temporarily to invest the
proceeds of this offering, pending their use as described under the caption "Use
of Proceeds." We expect to continue to be able to avoid registration
requirements of the 1940 Act. If we were required to register as an investment
company under the 1940 Act, we would become subject to substantial regulations
with respect to our capital structure, management, operations, transactions with
affiliates described in the Investment Company Act of 1940 and other matters.
Application of the provisions of this Act would have a material adverse effect
on our business.

DESCRIPTION OF CAPITAL STOCK

Our authorized capital stock consists of 60,000,000 shares of common stock,
par value $.001 per share, 40,000,000 shares of Class A stock, par value $.001
per share and 30,000,000 shares of preferred stock, par value $.01 per share. As
of March 8, 2000, 29,641,005 shares of our common stock were outstanding and
held by 698 shareholders of record and 2,789,511 shares of our Class A stock
were outstanding and held by 73 shareholders of record. The following is a
summary description of our capital stock. For more information, see our Restated
Certificate of Incorporation. A copy of this certificate is incorporated by
reference to the registration statement of which this prospectus forms a part.

COMMON STOCK AND CLASS A STOCK

General. The rights of holders of common stock and holders of Class A
stock are identical except for voting and conversion rights and restrictions on
transferability.

Voting Rights. The holders of Class A stock are entitled to ten votes per
share and the holders of common stock are entitled to one vote per share. Except
as otherwise required by law or as described below, holders of Class A stock
will vote together as a single class on all matters presented to the
shareholders for their vote or approval, including the election of directors.
Shareholders are not entitled to vote cumulatively

<PAGE>

for the election of directors and no class of outstanding common stock acting
alone is entitled to elect any directors.

Transfer Restrictions. Class A stock is subject to certain limitations on
transfer that do not apply to the common stock.

Dividends and Liquidation. Holders of Class A stock and holders of our
common stock have an equal right to receive dividends when and if declared by
our Board of Directors out of funds legally available therefor. If a dividend or
distribution payable in Class A stock is made on the Class A stock, we must also
make a pro rata and simultaneous dividend or distribution on the common stock
payable in shares of common stock. Conversely, if a dividend or distribution
payable in common stock is made on the common stock, we must also make a pro
rata and simultaneous dividend or distribution on the Class A stock payable in
shares of Class A stock. In the event of our liquidation, dissolution, or
winding up, holders of the shares of Class A stock and common stock are entitled
to share equally, share-for-share, in the assets available for distribution
after payment of all creditors and the liquidation preferences of our preferred
stock.

Optional Conversion Rights. Each share of Class A stock may, at any time
and at the option of the holder, be converted into one fully paid and
nonassessable share of common stock. Upon conversion, such shares of common
stock would not be subject to restrictions on transfer that applied to the
shares of Class A stock prior to conversion except to the extent such
restrictions are imposed under applicable securities laws.

The shares of common stock are not convertible into or exchangeable for
shares of Class A stock or any other of our shares or securities.

Other Provisions. Holders of Class A stock and common stock have no
preemptive rights to subscribe to any additional securities of any class which
we may issue and there are no redemption provisions or sinking fund provisions
applicable to either such class, nor is the Class A stock or the common stock
subject to calls or assessments.

Nasdaq National Market Listing. Our common stock is quoted on the Nasdaq
National Market. The current rules of the National Association of Securities
Dealers, Inc. (the "NASD") effectively preclude the trading or quotation through
the Nasdaq National Market of any securities of an issuer which has issued
securities or taken other corporate action that would have the effect of
nullifying, restricting, or disparately reducing the per share voting of an
outstanding class or classes of equity securities registered under section 12 of
the Exchange Act. Certain national securities exchanges have adopted similar
rules or policies. We do not intend to issue any additional shares of any stock
that would make it ineligible for inclusion on the Nasdaq National Market or any
national securities exchange. However, if we issue additional stock that causes
us to become ineligible for continued inclusion on the Nasdaq National Market,
then the ineligibility would be likely to materially reduce the liquidity of an
investment in our common stock and would likely depress its market value below
that which would otherwise prevail.

Transfer Agent and Registrar. The Transfer Agent and Registrar for the
common stock is American Stock Transfer & Trust Company.

PREFERRED STOCK

Our Restated Certificate of Incorporation allows us to issue up to
30,000,000 shares of preferred stock in one or more series and as may be
determined by our Board of Directors who may establish from time to time the
number of shares to be included in each such series, to fix the designation,
powers, preference and rights of the shares of each such series and any
qualifications, limitations, or restrictions thereof and to increase or decrease
the number of shares of any such series without any further vote or action by
the shareholders. Our Board of Directors may authorize, without shareholder
approval, the issuance of preferred stock with voting and conversion rights that
could adversely affect the voting power and other rights of holders of our
common stock. Preferred stock could thus be issued quickly with terms designed
to delay or prevent a change in control or to make the removal of management
more difficult. In certain circumstances, this could have the effect of
decreasing the market price of our common stock.

<PAGE>

REGISTRATION RIGHTS OF CERTAIN HOLDERS

Certain of our shareholders have registration rights. Under the agreements
between us and the holders of registration rights, certain holders may under
certain circumstances request that we file a registration statement under the
Securities Act and, upon such request and subject to certain minimum size
conditions, we will generally be required to use our best efforts to effect any
such registration. We are not generally required to effect more than two such
registrations. However, we are required under certain circumstances to effect an
unlimited number of Form S-3 or similar short form registrations for such
holders. We are generally obligated to bear the expenses, other than
underwriting discounts and sales commissions, of all of these registrations.

In addition, if we propose to register any of our securities, either for
our own account or for the account of other shareholders, with certain
exceptions, we are required to notify the holders noted above and to include in
such registration all of the shares of our common stock requested to be included
by such holders. In connection with this offering, we have notified each of the
holders who have registration rights and each holder other than the selling
shareholder has waived or intends to waive its rights to exercise its respective
registration rights.

RIGHTS PLAN

In September 1996, we adopted a Shareholder Rights Plan. As with most
shareholder rights agreements, the terms of our rights agreement are complex and
not easily summarized. This summary may not contain all of the information that
is important to you. Accordingly, you should carefully read our rights
agreement, which has been filed with the SEC.

Our rights agreement provides that each share of our common stock will have
one right to purchase a unit consisting of one-thousandth of a preferred share
at a purchase price of $120 per unit.

Initially, the rights under our rights agreement are attached to
outstanding certificates representing our common stock and no separate
certificates representing the rights will be distributed. The rights will
separate from our common stock and be represented by separate certificates
approximately 10 days after someone acquires or commences a tender offer for 20%
of our outstanding common stock.

After the rights separate from our common stock, certificates representing
the rights will be mailed to record holders of our common stock. Once
distributed, the rights certificates alone will represent the rights.

All shares of our common stock issued prior to the date the rights separate
from the common stock will be issued with the rights attached. The rights are
not exercisable until the date the rights separate from the common stock. The
rights will expire on October 18, 2006 unless earlier redeemed or exchanged by
us.

If an acquiror obtains or has the right to obtain 20% or more of our common
stock, then each right will entitle the holder to purchase a number of shares of
our common stock initially equal to two times the purchase price of each right,
unless the acquisition is made pursuant to a tender or exchange offer for all of
our outstanding shares at a price determined by a majority of our independent
directors. In this event, rights held by the acquiring person shall become null
and void.

In certain circumstances, a right will entitle the holder to purchase a
number of shares of common stock of the acquiror having a then current market
value of twice the right's purchase price.

Holders of rights will have no rights as our stockholders including the
right to vote or receive dividends, simply by virtue of holding the rights.

Our rights agreement may have anti-takeover effects. The rights may cause
substantial dilution to a person or group that attempts to acquire us.
Accordingly, the existence of the rights may deter acquirors from making
takeover proposals or tender offers. However, the rights are not intended to
prevent a takeover, but rather are designed to enhance the ability of our board
to negotiate with an acquiror on behalf of all the shareholders. In addition,
the rights should not interfere with a proxy contest.

<PAGE>

SELLING SHAREHOLDER

Amgen is one of our important collaborators and is an equal partner with us
in Amgen-Regeneron Partners. The following table sets forth certain information
with respect to the beneficial ownership of our common stock (before and after
giving effect to the issuance and sale of shares pursuant to this prospectus) as
of March 8, 2000 by Amgen.

<TABLE>
<CAPTION>
SHARES BEING
SHARES BENEFICIALLY OFFERED IF THE
OWNED UNDERWRITERS SHARES BENEFICIALLY
PRIOR TO THE OVER-ALLOTMENT OWNED
OFFERING OPTION IS AFTER THE OFFERING
-------------------- EXERCISED IN --------------------
NAME AND ADDRESS NUMBER PERCENT FULL NUMBER PERCENT
- ----------------------------------------------------- --------- ------- -------------- --------- -------
<S> <C> <C> <C> <C> <C>
Amgen Inc. .......................................... 4,916,808 15.2% 600,000 4,316,808 11.8%
One Amgen Center Drive
Thousand Oaks, CA 91320
</TABLE>

<PAGE>

UNDERWRITING

Merrill Lynch, Pierce, Fenner & Smith Incorporated, Lehman Brothers Inc.,
J.P. Morgan Securities Inc. and FleetBoston Robertson Stephens Inc. are acting
as representatives of each of the underwriters named below. Subject to the terms
and conditions described in a purchase agreement among us, the selling
shareholder and the underwriters, we have agreed to sell to the underwriters and
the underwriters severally have agreed to purchase from us the number of shares
of common stock listed opposite their names below.

<TABLE>
<CAPTION>
NUMBER
UNDERWRITER OF SHARES
----------- ---------
<S> <C>
Merrill Lynch, Pierce, Fenner & Smith
Incorporated...................................................................
Lehman Brothers Inc........................................................................
J.P. Morgan Securities Inc.................................................................
FleetBoston Robertson Stephens Inc.........................................................
---------
Total......................................................................... 4,000,000
=========
</TABLE>

The underwriters have agreed to purchase all of the shares sold under the
purchase agreement if any of these shares are purchased. If an underwriter
defaults, the purchase agreement provides that the purchase commitments of the
nondefaulting underwriters may be increased or the purchase agreement may be
terminated. The closings for the sale of shares to be purchased by the
underwriters are conditioned on one another.

We and the selling shareholder have agreed to indemnify the underwriters
against certain liabilities, including liabilities under the Securities Act, or
to contribute to payments the underwriters may be required to make in respect of
those liabilities.

The underwriters are offering the shares, subject to prior sale, when, as
and if issued to and accepted by them, subject to approval of legal matters by
their counsel, including the validity of the shares, and other conditions
contained in the purchase agreements, such as the receipt by the underwriters of
officers' certificates and legal opinions. The underwriters reserve the right to
withdraw, cancel or modify offers to the public and to reject orders in whole or
in part.

COMMISSIONS AND DISCOUNTS

The underwriters have advised us that the underwriters propose initially to
offer the shares to the public at the initial public offering price on the cover
page of this prospectus and to dealers at the price less a concession not in
excess of $ per share. The underwriters may allow, and the dealers may
reallow, a discount not in excess of $ per share to other dealers. After the
initial public offering, the public offering price, concession and discount may
be changed.

The following table shows the public offering price, underwriting discount
and proceeds before expenses to us. The information assumes either no
exercise or full exercise by the underwriters of their over-allotment options.

<TABLE>
<CAPTION>
WITH
PER SHARE WITHOUT OPTION OPTION
--------- -------------- --------
<S> <C> <C> <C>
Public offering price................................... $ $ $
Underwriting discount................................... $ $ $
Proceeds, before expenses, to Regeneron................. $ $ $
</TABLE>

The expenses of the offering, not including the underwriting discount, are
estimated at $550,000 and are payable by us.

OVER-ALLOTMENT OPTION

The selling shareholder has granted options to the underwriters to purchase
up to 600,000 additional shares at the public offering price less the
underwriting discount. The underwriters may exercise these options for 30 days
from the date of this prospectus solely to cover any over-allotments. If the
underwriters exercise

<PAGE>

these options, each will be obligated, subject to conditions contained in the
purchase agreements, to purchase a number of additional shares proportionate to
that underwriter's initial amount reflected in the above table.

NO SALES OF SIMILAR SECURITIES

We and our executive officers and directors and certain existing
shareholders, including Amgen have agreed, with exceptions, not to sell or
transfer any common stock for 90 days after the date of this prospectus without
first obtaining the written consent of Merrill Lynch. Specifically, we and these
other individuals or entities have agreed not to directly or indirectly:

o offer, pledge, sell or contract to sell any common stock,

o sell any option or contract to purchase any common stock,

o purchase any option or contract to sell any common stock,

o grant any option, right or warrant for the sale of any common stock,

o lend or otherwise dispose of or transfer any common stock,

o enter into any swap or other agreement that transfers, in whole or in
part, the economic consequence of ownership of any common stock whether
any such swap or transaction is to be settled by delivery of shares or
other securities, in cash or otherwise.

This lockup provision applies to common stock and to securities convertible
into or exchangeable or exercisable for or repayable with common stock. It also
applies to common stock owned now or acquired later by the person executing the
agreement or for which the person executing the agreement later acquires the
power of disposition.

We, however, may issue (1) shares upon the exercise of an option or warrant
or the conversion of a security outstanding on the date of this prospectus,
(2) shares or options to purchase shares granted pursuant to our existing and
future employee benefit plans and (3) shares pursuant to any non-employee
director stock plan or dividend reinvestment plan.

Procter & Gamble has agreed to a lockup provision for a period not to
exceed the earlier of (1) 90 days after the date of this prospectus and
(2) June 30, 2000.

The shares are quoted on the Nasdaq National Market under the symbol
"REGN."

UK SELLING RESTRICTIONS

Each underwriter has agreed that

o it has not offered or sold and will not offer or sell any shares of
common stock to persons in the United Kingdom, except to persons whose
ordinary activities involve them in acquiring, holding, managing or
disposing of investments (as principal or agent) for the purposes of
their businesses or otherwise in circumstances which do not constitute an
offer to the public in the United Kingdom within the meaning of the
Public Offers of Securities Regulations 1995;

o it has complied and will comply with all applicable provisions of the
Financial Services Act 1986 with respect to anything done by it in
relation to the common stock in, from or otherwise involving the United
Kingdom; and

o it has only issued or passed on and will only issue or pass on in the
United Kingdom any document received by it in connection with the
issuance of common stock to a person who is of a kind described in
Article 11(3) of the Financial Services Act 1986 (Investment
Advertisements) (Exemptions) Order 1996 as amended by the Financial
Services Act 1986 (Investment Advertisements) (Exemptions) Order 1997 or
is a person to whom such document may otherwise lawfully be issued or
passed on.

NO PUBLIC OFFERING OUTSIDE THE UNITED STATES

No action has been or will be taken in any jurisdiction (except in the
United States) that would permit a public offering of the shares of common
stock, or the possession, circulation or distribution of this prospectus or any
other material relating to our company, the selling stockholder or shares of our
common stock in any

<PAGE>

jurisdiction where action for that purpose is required. Accordingly, the shares
of our common stock may not be offered or sold, directly or indirectly, and
neither this prospectus nor any other offering material or advertisements in
connection with the shares of common stock may be distributed or published, in
or from any country or jurisdiction except in compliance with any applicable
rules and regulations of any such country or jurisdiction.

Purchasers of the shares offered by this prospectus may be required to pay
stamp taxes and other charges in accordance with the laws and practices of the
country of purchase in addition to the offering price on the cover page of this
prospectus.

PRICE STABILIZATION, SHORT POSITIONS

Until the distribution of the shares is completed, SEC rules may limit
underwriters and selling group members from bidding for and purchasing our
common stock. However, the underwriters may engage in transactions that
stabilize the price of the common stock, such as bids or purchases to peg, fix
or maintain that price.

If the underwriters create a short position in the common stock in
connection with the offering, i.e., if they sell more shares than are listed on
the cover of this prospectus, the underwriters may reduce that short position by
purchasing shares in the open market. The underwriters may also elect to reduce
any short position by exercising all or part of the over-allotment option
described above. Purchases of the common stock to stabilize its price or to
reduce a short position may cause the price of the common stock to be higher
than it might be in the absence of such purchases.

Neither we nor any of the underwriters makes any representation or
prediction as to the direction or magnitude of any effect that the transactions
described above may have on the price of the common stock. In addition, neither
we nor any of the underwriters makes any representation that the underwriters or
the lead manager will engage in these transactions or that these transactions,
once commenced, will not be discontinued without notice.

PASSIVE MARKET MAKING

In connection with this offering, underwriters and selling group members
may engage in passive market making transactions in the common stock on the
Nasdaq National Market in accordance with Rule 103 of Regulation M under the
Exchange Act during a period before the commencement of offers or sales of
common stock and extending through the completion of distribution. A passive
market maker must display its bid at a price not in excess of the highest
independent bid of that security. However, if all independent bids are lowered
below the passive market maker's bid, that bid must then be lowered when
specified purchase limits are exceeded.

OTHER RELATIONSHIPS

Some of the underwriters and their affiliates have engaged in, and may in
the future engage in, investment banking and other commercial dealings in the
ordinary course of business with us. They have received customary fees and
commissions for these transactions.

LEGAL MATTERS

Skadden, Arps, Slate, Meagher & Flom LLP, New York, New York will pass upon
the validity of our common stock offered by this prospectus for us. Shearman &
Sterling, New York, New York will pass upon certain legal matters in connection
with this offering for the underwriters.

<PAGE>

EXPERTS

The financial statements of Regeneron Pharmaceuticals, Inc. which are
incorporated in this Prospectus by reference to the Annual Report on Form 10-K
of Regeneron Pharmaceuticals, Inc. for the year ended December 31, 1999, have
been so incorporated in reliance on the report of PricewaterhouseCoopers LLP,
independent accountants, given on the authority of said firm as experts in
auditing and accounting.

The financial statements of Amgen-Regeneron Partners appearing in the
Regeneron Pharmaceuticals, Inc.'s 1999 Form 10-K have been audited by Ernst &
Young LLP, independent auditors, as set forth in their report thereon included
therein and incorporated herein by reference. Such financial statements are
incorporated herein by reference in reliance upon such report given on the
authority of such firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and special reports, proxy statements and other
information with the SEC. You may read and copy any documents we file at the
SEC's Public Reference Room at 450 Fifth Street, N.W., Washington, D.C. 20549
and at the Regional Offices of the SEC at 7 World Trade Center, 13th Floor, New
York, New York 10048 and Citicorp Center, 500 West Madison Street, Suite 1400,
Chicago, Illinois 60601. Please call the SEC at 1-800-SEC-0330 for further
information on the public reference rooms. The SEC maintains a site on the World
Wide Web at http://www.sec.gov that contains our SEC filings and reports, proxy
and information statements and other information regarding registrants.

The SEC allows us to "incorporate by reference" the information we file
with them, which means that we can disclose important information to you by
referring you to those documents. The information incorporated by reference is
considered to be part of this prospectus and information that we file later with
the SEC will automatically update and supersede this information. We incorporate
by reference the documents listed below and all future filings we make with the
SEC after the date of the initial registration statement and prior to
effectiveness of the registration statement and any filings thereafter and prior
to the termination of this offering with the SEC under Section 13(a), 13(c), 14,
or 15(d) of the Securities Exchange Act of 1934:

(1) our Annual Report on Form 10-K for the year ended December 31, 1999;
and

(2) the description of our common stock contained in Item 1 of our
Registration Statement on Form 8-A filed on February 20, 1991, as
amended by a Form 8 filed on March 27, 1991.

You may request a copy of these filings, at no cost, by writing or telephoning
us at the following address:

Regeneron Pharmaceuticals, Inc.
777 Old Saw Mill River Road
Tarrytown, New York 10591-6707
(914) 347-7000
Attention: Murray A. Goldberg
Chief Financial Officer

<PAGE>

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

4,000,000 SHARES

REGENERON PHARMACEUTICALS, INC.

COMMON STOCK

---------------------
PROSPECTUS
---------------------

MERRILL LYNCH & CO.
LEHMAN BROTHERS
J.P. MORGAN & CO.
ROBERTSON STEPHENS

MARCH , 2000
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------

<PAGE>

PART II
INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 14. OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION.

The following table sets forth all fees and expenses in connection with the
issuance and distribution of the securities being registered hereby (other than
underwriting discounts and commissions). All of such expenses, except the
Securities and Exchange Commission registration fee, the National Association of
Securities Dealers, Inc. ("NASD") filing fee and the NASDAQ listing fee are
estimated.

<TABLE>
<S> <C>
Securities and Exchange Commission registration fee........ $ 60,909.75
NASDAQ listing fee......................................... 17,500.00
NASD filing fee............................................ 23,687.88
Legal fees and expenses.................................... 190,000.00
Transfer Agent and Registrar fees and expenses............. 5,000.00
Accounting fees and expenses............................... 150,000.00
Blue sky fees and expenses (including counsel fees)........ 10,000.00
Printing expenses.......................................... 70,000.00
Miscellaneous.............................................. 22,902.37
-----------
Total............................................... $550,000.00
===========
</TABLE>

ITEM 15. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

Article Seven of the Registrant's Restated Certificate of Incorporation
requires indemnification of the Registrant's officers and directs that such
indemnification be made to the fullest extent permitted by the New York Business
Corporation Law.

Section 722 of the New York Business Corporation Law permits a corporation
to provide for the indemnification of the members of its board of directors and
its officers against actions or proceedings, or the threat thereof, by or in the
right of the corporation. In order to receive indemnification, such director or
officer must have (i) acted in good faith for a purpose which he reasonably
believed was in the best interest of the corporation, and (ii) in the case of a
criminal proceeding, also had no reasonable belief that such conduct was
unlawful.

Article IV of the Company's By-Laws provides that the directors and certain
other personnel of the Company shall be indemnified against expenses and certain
other liabilities arising out of legal actions brought or threatened against
them for their conduct on behalf of the Company, subject to certain
qualifications and provided that each such person acted in good faith and in a
manner that they reasonably believed was in the Company's best interest.

Each of the directors has entered into an agreement with the Company that
provides that the Company will indemnify such director to the fullest extent
permitted by the New York Business Corporation Law. The Company maintains
directors' and officers' liability insurance which insures against liabilities
that directors or officers of the Company may incur in such capacities.

Reference is made to the proposed Underwriting Agreement filed as
Exhibit 1 to this Registration Statement for certain provisions relating to the
indemnification of directors and officers of the Company against certain
liabilities under the Securities Act of 1933.

II-1

<PAGE>

ITEM 16. EXHIBITS

<TABLE>
<CAPTION>
EXHIBIT
NUMBER DESCRIPTION
- ------ -----------------------------------------------------------------------------------------------------------
<S> <C> <C>
*1 -- Form of Underwriting Agreement.
4.1 -- Stock Purchase Agreement dated January 13, 1988, by and between the Company, Leonard S. Schleifer and
ML Venture Partners II, L.P. (the "Stock Purchase Agreement"). Incorporated by reference to
Exhibit 10.1 to Regeneron's Registration Statement on Form S-1 (File No. 33-39043) (the "Regeneron
S-1").
4.2 -- Amendment to the Stock Purchase Agreement dated March 3, 1989. Incorporated by reference to
Exhibit 10.2 to the Regeneron S-1.
4.3 -- Letter Agreement dated November 27, 1989, amending the Stock Purchase Agreement. Incorporated by
reference to Exhibit 10.13 to the Regeneron S-1.
4.4 -- Class B Convertible Preferred Stock Purchase Agreement dated November 22, 1988, by and between the
Company and each purchaser set forth on Exhibit A thereto. Incorporated by reference to Exhibit 10.3
to the Regeneron S-1.
4.5 -- Class C Convertible Preferred Stock Purchase Agreement dated March 20, 1989, by and between the
Company and Sumitomo Chemical Company, Limited. Incorporated by reference to Exhibit 10.4 to the
Regeneron S-1.
4.6 -- Class D Convertible Preferred Stock Purchase Agreement dated August 31, 1990, by and between the
Company and Amgen Inc. Incorporated by reference to Exhibit 10.9 to the Regeneron S-1.
4.7 -- Registration Rights Agreement, dated as of July 22, 1993, by and between the Company and Glaxo Group
Limited. Incorporated by reference to Exhibit 4.7 to Regeneron's Registration Statement on Form S-3
(File No. 33-66788).
4.8 -- Registration Rights Agreement, dated as of April 15, 1996, by and between the Company and Amgen Inc.
Incorporated by reference to Exhibit 10.3 to Regeneron's Form 10Q for the quarter ended June 30,
1996, filed August 14, 1996.
4.9 -- Registration Rights Agreement, dated as of June 27, 1996, by and between the Company and Medtronic,
Inc. Incorporated by reference to Exhibit 10.6 to Regeneron's Form 10Q for the quarter ended
June 30, 1996, filed August 14, 1996.
4.10 -- Registration Rights Agreement, dated as of December 11, 1996, by and between the Company and Procter
& Gamble Pharmaceuticals. Incorporated by reference to Exhibit 10.30 to Regeneron's Form 10K for the
fiscal year ended December 31, 1996, filed March 26, 1997.
4.11 -- Registration Rights Agreement, dated as of May 13, 1997, by and between the Company and Procter &
Gamble Pharmaceuticals. Incorporated by reference to Exhibit 10.3 to Regeneron's Form 10Q for the
quarter ended June 30, 1997, filed August 12, 1997.
4.12 -- Form of Certificate of shares of common stock. Incorporated by reference to Exhibit (a) to the
Company's Form 8-A, filed with the Commission on February 20, 1991.
5 -- Opinion of Skadden, Arps, Slate, Meagher & Flom LLP.
23.1 -- Consent of PricewaterhouseCoopers LLP.
23.2 -- Consent of Ernst & Young LLP, Independent Auditors.
23.3 -- Consent of Skadden, Arps, Slate, Meagher & Flom LLP. Included in Exhibit 5.
24 -- Powers of Attorney. Included in the signature page of this Registration Statement.
</TABLE>

- ------------------
* To be filed by amendment.

ITEM 17. UNDERTAKINGS.

The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933 (the "Securities
Act"), each filing of the Registrant's annual report pursuant to
section 13(a) or section 15(d) of the Securities Exchange Act of 1934 (and,
where applicable, each filing of an

II-2

<PAGE>

employee benefit plan's annual report pursuant to section 15(d) of the
Securities Exchange Act of 1934) that is incorporated by reference in the
Registration Statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

Insofar as indemnification for liabilities arising under the Securities Act
may be permitted to directors, officers and controlling persons of the
Registrant pursuant to the provisions described in "Item 14--Indemnification of
Directors and Officers" above, or otherwise, the Registrant has been advised
that in the opinion of the Commission such indemnification is against public
policy as expressed in the Securities Act and is, therefore, unenforceable. In
the event that a claim for indemnification against such liabilities (other than
the payment by the Registrant of expenses incurred or paid by a director,
officer, or controlling person of the Registrant in the successful defense of
any action, suit, or proceeding) is asserted by such director, officer, or
controlling person in connection with the securities being registered, the
Registrant will, unless in the opinion of its counsel the matter has been
settled by controlling precedent, submit to a court of appropriate jurisdiction
the question whether such indemnification by it is against public policy as
expressed in the Securities Act and will be governed by the final adjudication
of such issue.

The undersigned Registrant hereby undertakes that:

(1) For purposes of determining any liability under the Securities
Act, the information omitted from the form of prospectus filed as part of
this Registration Statement in reliance upon Rule 430A and contained in a
form of prospectus filed by the Registrant pursuant to Rule 424(b)(1) or
(4) or 497(h) under the Securities Act shall de deemed to be part of this
Registration Statement as of the time it was declared effective.

(2) For the purpose of determining any liability under the Securities
Act, each post-effective amendment that contains a form of prospectus shall
be deemed to be a new Registration Statement relating to the securities
offered therein and the offering of such securities at that time shall be
deemed to be the initial bona fide offering thereof.

II-3

<PAGE>

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-3 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Tarrytown, State of New York on March 10, 2000.

REGENERON PHARMACEUTICALS, INC.

By: /s/ LEONARD S. SCHLEIFER, M.D., PH.D.
-------------------------------------
Leonard S. Schleifer, M.D., Ph.D.
President and Chief Executive
Officer

PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THIS
REGISTRATION STATEMENT HAS BEEN SIGNED BY THE FOLLOWING PERSONS IN THE
CAPACITIES AND ON THE DATES INDICATED. EACH PERSON WHOSE SIGNATURE APPEARS BELOW
HEREBY AUTHORIZES LEONARD S. SCHLEIFER AND MURRAY A. GOLDBERG, JOINTLY AND
SEVERALLY, WITH FULL POWER TO EACH, TO EXECUTE IN THE NAME AND ON BEHALF OF SUCH
PERSON ANY AMENDMENT (INCLUDING ANY POST-EFFECTIVE AMENDMENTS) TO THIS
REGISTRATION STATEMENT (OR ANY OTHER REGISTRATION STATEMENT FOR THE SAME
OFFERING THAT IS TO BE EFFECTIVE UPON FILING PURSUANT TO RULE 462(B) UNDER THE
SECURITIES ACT) AND TO FILE THE SAME, WITH EXHIBITS THERETO AND OTHER DOCUMENTS
IN CONNECTION THEREWITH, MAKING SUCH CHANGES IN THIS REGISTRATION STATEMENT AS
THE PERSON(S) SO ACTING DEEMS APPROPRIATE AND APPOINTS EACH OF SUCH PERSONS,
EACH WITH FULL POWER OF SUBSTITUTION, ATTORNEY-IN-FACT TO SIGN ANY AMENDMENT
(INCLUDING ANY POST-EFFECTIVE AMENDMENT) TO THIS REGISTRATION STATEMENT (OR ANY
OTHER REGISTRATION STATEMENT FOR THE SAME OFFERING THAT IS TO BE EFFECTIVE UPON
FILING PURSUANT TO RULE 462(B) UNDER THE SECURITIES ACT) AND TO FILE THE SAME,
WITH EXHIBITS THERETO AND OTHER DOCUMENTS IN CONNECTION THEREIN.

<TABLE>
<CAPTION>
SIGNATURE TITLE DATE
- ------------------------------------------ ------------------------------------------------- ---------------

<C> <S> <C>
/s/ P. ROY VAGELOS, M.D. Chairman of the Board March 10, 2000
- ------------------------------------------
P. Roy Vagelos, M.D.

/s/ LEONARD S. SCHLEIFER, M.D., PH.D President, Chief Executive Officer and Director March 10, 2000
- ------------------------------------------ (Principal Executive Officer)
Leonard S. Schleifer, M.D., Ph.D.

/s/ MURRAY A. GOLDBERG Vice President, Finance & Administration, Chief March 10, 2000
- ------------------------------------------ Financial Officer, Treasurer and Assistant
Murray A. Goldberg Secretary (Principal Financial Officer)

/s/ DOUGLAS S. MCCORKLE Controller and Assistant Treasurer March 10, 2000
- ------------------------------------------
Douglas S. McCorkle

/s/ CHARLES A. BAKER Director March 10, 2000
- ------------------------------------------
Charles A. Baker

/s/ MICHAEL S. BROWN, M.D. Director March 10, 2000
- ------------------------------------------
Michael S. Brown, M.D.

/s/ ALFRED G. GILMAN, M.D., PH.D. Director March 10, 2000
- ------------------------------------------
Alfred G. Gilman, M.D., Ph.D.

/s/ JOSEPH L. GOLDSTEIN, M.D. Director March 10, 2000
- ------------------------------------------
Joseph L. Goldstein, M.D.

/s/ FRED A. MIDDLETON Director March 10, 2000
- ------------------------------------------
Fred A. Middleton

/s/ ERIC M. SHOOTER, PH.D. Director March 10, 2000
- ------------------------------------------
Eric M. Shooter, Ph.D.

/s/ GEORGE L. SING Director March 10, 2000
- ------------------------------------------
George L. Sing
</TABLE>

II-4

<PAGE>

EXHIBIT INDEX

- ------------------
* To be filed by amendment.

<PAGE>

Exhibit 5.1

SKADDEN LETTERHEAD

March 10, 2000

Regeneron Pharmaceuticals, Inc.
777 Old Saw Mill River Road
Tarrytown, New York 10591-6707

Re: Regeneron Pharmaceuticals, Inc.
Registration Statement on Form S-3

Ladies and Gentlemen:

We have acted as special counsel to Regeneron Pharmaceuticals,
Inc., a New York corporation (the "Company"), in connection with the public
offering by the Company of up to 4,000,000 shares (the "Company Shares") of the
Company's Common Stock, par value $0.001 per share (the "Common Stock"), and by
a shareholder of the Company of an additional 600,000 shares of Common Stock
(the "Over-Allotment Shares") that are subject to an over-allotment option
granted to the Underwriters (as defined below).

This opinion is being furnished in accordance with the
requirements of Item 601(b)(5) of Regulation S-K under the Securities Act of
1933, as amended (the "Securities Act").

In connection with this opinion, we have examined originals or
copies, certified or otherwise identified to our satisfaction, of (i) the
Registration Statement on Form S-3 (File No. 333-31764), as filed with the
Securities and Exchange Commission (the "Commission") on March 6, 2000, under
the Securities Act, and Amendment No. 1 to the Registration Statement, as filed
with the Commission on the date hereof (such Registration Statement, as so
amended, being hereinafter referred to as the "Registration Statement"); (ii)
the form of the Underwriting Agreement (the "Underwriting Agreement") proposed
to be entered into between the

1
<PAGE>

Regeneron Pharmaceuticals, Inc.
March 10, 20

Company, as issuer, the selling shareholder, and Merrill Lynch, Pierce, Fenner &
Smith Incorporated, Lehman Brothers Inc., J.P. Morgan Securities Inc. and
FleetBoston Robertson Stephens Inc., as underwriters (the "Underwriters"), filed
as an exhibit to the Registration Statement; (iii) a specimen certificate
evidencing the Common Stock; (iv) the Restated Certificate of Incorporation of
the Company, as presently in effect; (v) the By-laws of the Company, as
presently in effect; and (vi) Stock and Warrant Purchase Agreement dated as of
April 15, 1996 between the Company and Amgen Inc. We have also examined
originals or copies, certified or otherwise identified to our satisfaction, of
such records of the Company and such agreements, certificates of public
officials, certificates of officers or other representatives of the Company and
others, and such other documents, certificates and records as we have deemed
necessary or appropriate as a basis for the opinion set forth herein.

In our examination, we have assumed the legal capacity of all
natural persons, the genuineness of all signatures, the authenticity of all
documents submit ted to us as originals, the conformity to original documents of
all documents submitted to us as certified, conformed or photostatic copies and
the authenticity of the originals of such latter documents. In making our
examination of documents executed or to be executed by parties other than the
Company, we have assumed that such parties had or will have the power, corporate
or other, to enter into and perform all obligations thereunder and have also
assumed the due authorization by all requisite action, corporate or other, and
execution and delivery by such parties of such documents and the validity and
binding effect thereof. As to any facts material to the opinion expressed herein
which we have not independently established or verified, we have relied upon
statements and representations of officers and other representatives of the
Company and others. We have also assumed that the Company has received the
entire amount of the consideration contemplated by the resolutions of the Board
of Directors of the Company authorizing the original issuance of the
Over-Allotment Shares.

Members of our firm are admitted to the bar in the State of New
York, and we do not express any opinion as to the laws of any other
jurisdiction.

Based upon and subject to the foregoing, we are of the opinion
that:

2
<PAGE>

Regeneron Pharmaceuticals, Inc.
March 10, 20

1. When (i) the Registration Statement becomes effective under
the Securities Act; (ii) the Underwriting Agreement has been duly executed and
delivered; and (iii) the certificates representing the Company Shares, in the
form of the specimen certificates examined by us, have been manually signed by
an authorized officer of the transfer agent and registrar for the Common Stock
and registered by such transfer agent and registrar, and delivered to and paid
for by the Underwriters at a price per share not less than the per share par
value of the Common Stock as contemplated by the Underwriting Agreement, the
issuance and sale of the Company Shares will have been duly authorized, and the
Company Shares will be validly issued, fully paid and nonassessable.

2. The Over-Allotment Shares have been duly authorized and
validly issued and are fully paid and nonassessable.

In connection with rendering the opinion set forth above, we draw
your attention to Section 630 of the New York Business Corporation Law (the
"NYBCL"), which may impose certain liabilities on certain shareholders of New
York corporations that have no shares listed on a national securities exchange
or regularly quoted in an over-the-counter market. Section 630 of the NYBCL does
not presently apply to the Company, and we have assumed that such section will
continue to be inapplicable to the Company.

We hereby consent to the filing of this opinion with the
Commission as an exhibit to the Registration Statement. We also consent to the
reference to our firm under the caption "Legal Matters" in the Registration
Statement. In giving such consent, we do not thereby admit that we are included
in the category of persons whose consent is required under Section 7 of the
Securities Act or the rules and regulations of the Commission.

Very truly yours,

/s/ Skadden, Arps, Slate, Meagher & Flom

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EXHIBIT 23.1

CONSENT OF INDEPENDENT ACCOUNTANTS

We hereby consent to the incorporation by reference in this Registration
Statement on Form S-3 of our report, which is based in part on the report of
other auditors, dated February 8, 2000 relating to the financial statements,
which appears in Regeneron Pharmaceuticals, Inc.'s Annual Report on Form 10-K
for the year ended December 31, 1999. We also consent to the reference to us
under the heading "Experts" in such Registration Statement.

PRICEWATERHOUSECOOPERS LLP

New York, New York
March 9, 2000

<PAGE>

EXHIBIT 23.2

CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS

We consent to the reference to our firm under the caption "Experts" in the
Registration Statement (Form S-3) and related Prospectus of Regeneron
Pharmaceuticals, Inc. for the registration of 4,000,000 shares of its common
stock and to the incorporation by reference therein of our report dated
February 8, 2000, with respect to the financial statements of Amgen Regeneron
Partners included in Regeneron Pharmaceuticals, Inc.'s Annual Report
(Form 10-K) for the year ended December 31, 1999, filed with the Securities and
Exchange Commission.

ERNST & YOUNG LLP

Los Angeles, California
March 10, 2000