ATryn(R) Market Authorization Transferred To LEO Pharma A/S.

FRAMINGHAM, Mass. -- GTC Biotherapeutics, Inc. ("GTC", Nasdaq: GTCB) announced today that the market authorization of ATryn([R]) for the prophylaxis of venous thromboembolism in surgery of patients with congenital antithrombin deficiency has been transferred to its distribution and development partner, LEO Pharma A/S, following approval by the European Commission. ATryn([R]) is a recombinant form of human antithrombin. Antithrombin is normally found in human plasma and has both anticoagulant and anti-inflammatory properties. The approval of the transfer of the market authorization enables LEO to enter into negotiation of reimbursement rates as part of preparing for the commercial launch of ATryn([R]) in Europe on a country-by-country basis. The initial launch is being planned for around the end of the second quarter 2007.

In addition, LEO is conducting a phase II study of ATryn([R]) in Europe for the treatment of disseminated intravascular coagulation, or DIC, associated with severe sepsis. LEO has initiated the regulatory approval procedures to enable the opening of clinical sites and recruitment of patients into the study. GTC is continuing to supply the product to LEO to conduct this study.

Meeting these objectives in the development of the ATryn([R]) program supports GTC's previous guidance that pro-forma cash and marketable securities at the end of 2006 will be approximately $50 million. While actual cash and marketable securities at the end of 2006 will be approximately $43.9 million, the pro-forma amount includes the scheduled completion in early January of the third and final tranche of the previously announced $25 million total investment by LFB Biotechnologies, as well as scheduled payments for delivery of a portion of the phase II clinical supply to LEO in January that was begun in late 2006. GTC expects to use $26 to 29 million of cash in 2007 on a pro-forma basis. This forecast is net of cash received from operations, but excludes the items included in the 2006 year end pro-forma cash balance. The net cash use for 2007 includes forecasted sales of ATryn([R]) in the approved indication as well as to LEO for the DIC study. This forecast also reflects lower debt service payments due to refinancing of the loan with GE Capital in the last week of December 2006. This debt refinancing extended the amortization period from three to ten years and provided an additional $2.8 million of proceeds to GTC.

The 2007 cash use forecast includes planned support for completion of GTC's phase III study of ATryn([R]) in the hereditary deficiency indication for the United States, the filing of a Biologics License Application in the United States, development of the recombinant human factor VIIa production system with LFB Biotechnologies, and preclinical activities in GTC's recombinant human alpha-1 antitrypsin and CD137 monoclonal antibody programs. The phase II DIC study activities in 2007 will be conducted and funded by LEO.

Background on the ATryn([R]) DIC Study

DIC often develops as a result of severe sepsis. This is a large unmet medical need with approximately 220,000 cases in Europe and 250,000 cases in the United States with 50% mortality. Analysis of previous clinical experience indicates that treatment with antithrombin, without the concomitant use of heparin, has the potential to reduce the rate of mortality.

LEO's phase II study is based on Scientific Advice received from the European Medicines Agency. Approximately 200 patients are planned to be included in this study which is intended to define the optimum dosage and design for use in a subsequent phase III study. Recruitment into the phase II study is expected to take approximately 12 months.

About GTC Biotherapeutics, Inc.

GTC Biotherapeutics develops, produces, and commercializes therapeutic proteins through transgenic animal technology. In August 2006, ATryn([R]), GTC's recombinant form of human antithrombin, was approved by the European Commission for use in patients with hereditary antithrombin deficiency undergoing surgical procedures. This was the first approval anywhere in the world of a therapeutic protein produced from a transgenic animal. ATryn([R]) is in phase III studies to support a filing in the United States requesting approval in the hereditary deficiency indication. In addition, GTC established a strategic collaboration with LFB Biotechnologies of France to jointly develop recombinant forms of human plasma proteins and monoclonal antibodies. The first program of the collaboration will be to develop recombinant human factor VIIa as a potential treatment for hemophilia in patients with antibodies to other coagulation factors.

GTC has also recently been granted a patent in the United States through 2021 for the production of any therapeutic protein in the milk of any transgenic mammal. GTC's transgenic production platform is particularly well suited to enabling cost effective development of proteins that are difficult to express in traditional recombinant production systems as well as those that are required in large volumes. Additional information is available on the GTC web site, http://www.gtc-bio.com.

This press release contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995, including without limitation statements regarding the planned completion of LFB Biotechnologies' investment in GTC, the anticipated cash payments receivable upon delivery of clinical supplies of ATryn([R]) to LEO, the expected commercial launch of ATryn([R])in Europe, GTC's projected pro-forma cash balance at the end of 2006 and its projected net cash use for 2007. Such forward-looking statements are subject to a number of risks, uncertainties and other factors that could cause actual results to differ materially from future results expressed or implied by such statements. Factors that may cause such differences include, but are not limited to, the risks and uncertainties discussed in GTC's most recent Annual Report on Form 10-K and its other periodic reports filed with the Securities and Exchange Commission, including the risks and uncertainties associated with the development of therapeutic proteins and dependence upon the actions of strategic partners and regulatory agencies. GTC cautions investors not to place undue reliance on the forward-looking statements contained in this release. These statements speak only as of the date of this document, and GTC undertakes no obligation to update or revise the statements, except as may be required by law.