EXHIBIT 99(a)
                                                                   -------------

FOR IMMEDIATE RELEASE


             REGENERON INITIATES PHASE II CLINICAL TRIAL OF IL1 TRAP
                      IN PATIENTS WITH RHEUMATOID ARTHRITIS

            Lead Compound in Regeneron's Custom-designed Trap Program
                               Advances in Clinic

Tarrytown, NY - July 24, 2002 - Regeneron Pharmaceuticals, Inc. (Nasdaq: REGN)
today announced that it has initiated a dose-ranging Phase II trial to study the
safety and efficacy of the Interleukin-1 (IL1) Trap in patients with rheumatoid
arthritis (RA).

The multi-center Phase II trial is a randomized, placebo-controlled,
double-blind study in patients with active RA, who have had an inadequate
response to at least one disease-modifying anti-rheumatic medicine. The study
will involve approximately 200 participants, who will be randomized equally into
placebo or one of three fixed-dose groups (25, 50, or 100 milligrams) to receive
self-administered, weekly subcutaneous injections. The double-blind treatment
period will be 12 weeks, and participants will also be evaluated for 10 weeks
following treatment. The American College of Rheumatology (ACR20) criteria for
improvement in RA as a function of IL1Trap dose will be the primary end-point.

"Despite the recent advances in the treatment of rheumatoid arthritis, there is
still a major need for new treatment options for patients suffering from this
disease," noted Leonard S. Schleifer, M.D., Ph.D., Regeneron's President and
Chief Executive Officer. "The IL1 Trap is a highly potent blocker of
Interleukin-1 that works through a new mechanism of action. The advancement of
this molecule into Phase II is an important milestone for our research program
that uses a



thorough understanding of disease biology to validate pharmaceutical targets and
discover novel therapeutic candidates for development."

"The IL1 Trap is the leading candidate in our proprietary Trap program and is an
excellent example of the therapeutic potential of these custom-designed
molecules," noted Neil Stahl, Ph.D., Senior Vice President of Preclinical
Development and Biomolecular Science. "With this cornerstone of our Trap
franchise entering Phase II testing, we are extremely excited about the
potential of building a premier pipeline of internally derived product
candidates based on our Trap technology."

ABOUT REGENERON

Regeneron is a biopharmaceutical company that discovers, develops, and intends
to commercialize therapeutic medicines for the treatment of serious medical
conditions. Regeneron has therapeutic candidates in clinical trials for the
potential treatment of obesity, rheumatoid arthritis, and cancer, and has
preclinical programs in asthma, allergies, and other diseases and disorders.
Regeneron's platform technologies include Targeted GenomicsTM, FunctionomicsTM,
and Designer Protein TherapeuticsTM.

THIS NEWS RELEASE DISCUSSES HISTORICAL INFORMATION AND INCLUDES FORWARD-LOOKING
STATEMENTS ABOUT REGENERON AND ITS PRODUCTS, PROGRAMS, FINANCES, AND BUSINESS,
ALL OF WHICH INVOLVE A NUMBER OF RISKS AND UNCERTAINTIES, SUCH AS RISKS
ASSOCIATED WITH PRECLINICAL AND CLINICAL DEVELOPMENT OF DRUGS AND BIOLOGICS,
DETERMINATIONS BY REGULATORY AND ADMINISTRATIVE GOVERNMENTAL AUTHORITIES,
COMPETITIVE FACTORS, TECHNOLOGICAL DEVELOPMENTS, THE AVAILABILITY AND COST OF
CAPITAL, THE COSTS OF DEVELOPING, PRODUCING, AND SELLING PRODUCTS, THE POTENTIAL
FOR ANY COLLABORATION AGREEMENT TO BE CANCELED OR TO TERMINATE WITHOUT ANY
PRODUCT SUCCESS, AND OTHER MATERIAL RISKS. A MORE COMPLETE DESCRIPTION OF THESE
RISKS CAN BE FOUND IN REGENERON'S FILINGS WITH THE UNITED STATES SECURITIES AND
EXCHANGE COMMISSION, INCLUDING ITS FORM 10-K FOR THE YEAR ENDED DECEMBER 31,
2001 AND THE FORM 10-Q FOR THE QUARTER ENDED MARCH 31, 2002.


REGENERON DOES NOT UNDERTAKE ANY OBLIGATION TO UPDATE PUBLICLY ANY
FORWARD-LOOKING STATEMENT, WHETHER AS A RESULT OF NEW INFORMATION, FUTURE
EVENTS, OR OTHERWISE, UNLESS REQUIRED BY LAW.

                                       ###

Investor Relations Contact:         Charles Poole
                                    Vice President, Investor Relations
                                    Regeneron Pharmaceuticals, Inc.
                                    charles.poole@regn.com
                                   (914) 345-7641

Media Contact:                      Jeanne Abi-Nader
                                    Vice President
                                    Robinson, Lerer, Montgomery
                                    jabi-nader@rlmnet.com
                                    (212) 484-7954

Additional information about Regeneron and recent news releases are available on
Regeneron's Worldwide Web Home Page at www.regn.com. Fax copies of news releases
can be obtained from Regeneron's News-on-Demand Service by dialing (800)
311-0841.