EXHIBIT 99.1

CONTACT:
Justine E. Koenigsberg
Manager, Corporate Communications
(617) 349-0271



FOR IMMEDIATE RELEASE


TKT REGAINS RIGHTS TO SECOND GENE-ACTIVATED(R) PROTEIN
FROM AVENTIS PHARMA


CAMBRIDGE, MA, DECEMBER 8, 2000-- Transkaryotic Therapies, Inc. (Nasdaq: TKTX)
today announced it has reacquired worldwide commercial rights to GA-II, a second
Gene-Activated(R)protein in development, from Aventis Pharma, the pharmaceutical
company of Aventis S.A. (NYSE: AVE). Financial terms were not disclosed.

"GA-II is a top priority program at TKT, and we are pleased to have reached
agreement with Aventis to reacquire rights to the product. We have benefited
from Aventis' expertise in moving the protein from basic research to preclinical
testing and into clinical development, and I believe we have the ability to
aggressively move this program into pivotal trials and beyond, " said Richard F
Selden, M.D., Ph.D., President and Chief Executive Officer of TKT. "Aventis has
been and continues to be instrumental in the development of our lead
Gene-Activated protein, Dynepo(TM), and we very much appreciate their effort on
both Gene-Activated protein programs."

Frank Douglas, M.D., Ph.D., Executive Vice President, Head Drug Innovation and
Approval of Aventis Pharma said, "Based on our collaboration over the past five
years we believe that TKT is well positioned to bring this program forward. We
wish TKT success in the future development of this product."

In December 1999, Aventis Pharma filed an Investigational New Drug Application
to commence Phase I clinical testing of GA-II. The Phase I study in healthy
volunteers was recently completed, and TKT expects to begin Phase II testing of
the protein next year. TKT's approach is based on the activation of genes
encoding therapeutic proteins in human cells rather than the


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cloning and transfer of these genes. TKT believes that its approach will allow
it to develop and commercialize a number of therapeutic proteins, including
potentially improved versions of many that are currently marketed.

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(R) 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.


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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 TKT's Annual Report on Form 10-K for
the year ended December 31, 1999 and updated in TKT's Quarterly Report on Form
10-Q for the quarter ended September 30, 2000, which are both on file with the
Securities and Exchange Commission and incorporated herein by reference. These
important factors include risks as to whether TKT's products, such as GA-II,
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 TKT's products, such as GA-II, 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 TKT is involved or may become
involved; competition; and TKT's dependence on collaborators.

         Gene-Activated(R) is a registered trademark and Niche Protein(TM),
         TKT(TM), and Transkaryotic Therapy(TM) are trademarks of Transkaryotic
         Therapies, Inc. Dynepo(TM) is a trademark of Aventis Pharma.

         Please visit our web site at www.tktx.com for additional information
         about Transkaryotic Therapies, Inc.



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