EXHIBIT 99.1

CONTACT:
Justine E. Koenigsberg
Transkaryotic Therapies, Inc.
(617) 349-0271


FOR IMMEDIATE RELEASE



   TKT ANNOUNCES PATENT INFRINGEMENT SUIT BY GENZYME RELATING TO REPLAGAL(TM)

CAMBRIDGE, MA, JULY 25, 2000 -- Transkaryotic Therapies, Inc. (Nasdaq: TKTX)
today announced that Genzyme Corporation has brought suit against TKT in the
United States District Court of Delaware in Wilmington claiming that TKT's
activities relating to Replagal(TM) (agalsidase alfa) infringe one or more
claims of U.S. Patent No. 5,356,804. Replagal(TM) is TKT's investigational
enzyme replacement therapy for the treatment OF Fabry disease. TKT was the first
company to conduct human clinical testing for this disorder and submitted a
Biologics License Application (BLA) to the U.S. Food and Drug Administration
seeking marketing approval of Replagal(TM) on June 16, 2000.

Richard F Selden, M.D., Ph.D., President and Chief Executive Officer of TKT
stated, "We strongly believe that TKT's activities relating to Replagal(TM) do
not infringe the `804 patent, and, in addition, that tHE patent is not valid. We
intend to vigorously defend this lawsuit and expect to prevail. It is a shame
that Genzyme has chosen to compete based on a frivolous lawsuit rather than on
the merits of their product. Furthermore, with over 5,000 rare diseases
affecting 20 million Americans, Genzyme is clearly wasting resources that could
be better allocated toward helping patients."

Transkaryotic Therapies, Inc. (TKT) is a biopharmaceutical company dedicated to
the development and commercialization of products based on its three proprietary
development platforms: Gene-Activated(TM) proteins, Niche Protein(TM) products,
and Gene Therapy. The Company's gene activation technology is A proprietary
approach to the large-scale production of therapeutic proteins, which does not
require the cloning of genes and their






subsequent insertion into non-human cell lines. TKT's Niche Protein product
platform is based on protein replacement for the treatment of rare genetic
diseases, a group of disorders characterized by the absence of certain metabolic
enzymes. The Company's Gene Therapy technology, known as Transkaryotic
Therapy(TM), is focused on the commercialization of non-viral, EX VIvo gene
therapy products fOR the long-term treatment of chronic protein deficiency
states.


THIS PRESS RELEASE CONTAINS FORWARD-LOOKING STATEMENTS THAT INVOLVE A NUMBER OF
RISKS AND UNCERTAINTIES. FOR THIS PURPOSE, ANY STATEMENTS CONTAINED HEREIN THAT
ARE NOT STATEMENTS OF HISTORICAL FACT MAY BE DEEMED TO BE FORWARD-LOOKING
STATEMENTS. WITHOUT LIMITING THE FOREGOING, THE WORDS, "BELIEVES,"
"ANTICIPATES," "PLANS," "EXPECTS," "INTENDS," AND SIMILAR EXPRESSIONS ARE
INTENDED TO IDENTIFY FORWARD-LOOKING STATEMENTS. IMPORTANT FACTORS THAT COULD
CAUSE ACTUAL RESULTS TO DIFFER MATERIALLY FROM THE EXPECTATIONS DESCRIBED IN
THESE FORWARD-LOOKING STATEMENTS ARE SET FORTH UNDER THE CAPTION "CERTAIN
FACTORS THAT MAY AFFECT FUTURE RESULTS" IN THE COMPANY'S ANNUAL REPORT ON FORM
10-K FOR THE YEAR ENDED DECEMBER 31, 1999 WHICH IS ON FILE WITH THE SECURITIES
AND EXCHANGE COMMISSION AND INCORPORATED HEREIN BY REFERENCE. THESE IMPORTANT
FACTORS INCLUDE RISKS AS TO WHETHER TKT'S PRODUCTS WILL ADVANCE IN THE CLINICAL
TRIALS PROCESS, THE TIMING OF SUCH CLINICAL TRIALS, WHETHER THE CLINICAL TRIAL
RESULTS WILL WARRANT CONTINUED PRODUCT DEVELOPMENT, AND WHETHER THE COMPANY'S
PRODUCTS WILL RECEIVE APPROVAL FROM THE U.S. FOOD AND DRUG ADMINISTRATION OR
EQUIVALENT REGULATORY AGENCIES, AND, IF SUCH PRODUCTS RECEIVE APPROVAL, WHETHER
THEY WILL BE SUCCESSFULLY MARKETED; THE RESULTS OF ANY PATENT LITIGATION IN
WHICH THE COMPANY IS INVOLVED OR MAY BECOME INVOLVED; COMPETITION; AND THE
COMPANY'S DEPENDENCE ON COLLABORATORS.

GENE-ACTIVATED(TM), NICHE PROTEIN(TM), REPLAGAL(TM), TKT(TM), AND TRANSKARYOTIC
THERAPY(TM) ARE TRADEMARKS OF TRANSKARYOTIC THERAPIES, INC.

PLEASE VISIT OUR WEB SITE AT WWW.TKTX.COM FOR ADDITIONAL INFORMATION ABOUT
TRANSKARYOTIC THERAPIES, INC.

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