Exhibit 99.1

CONTACT:

GTC Biotherapeutics, Inc.

William K. Heiden

Chairman, President and Chief Executive Officer

(508) 370-5277 or william.heiden@gtc-bio.com

GTC BIOTHERAPEUTICS REPORTS SECOND QUARTER 2010 FINANCIAL RESULTS

FRAMINGHAM, MA – July 27, 2010 — GTC Biotherapeutics, Inc. (“GTC”, OTCBB: GTCB) today reported its financial results for the second fiscal quarter ended July 4, 2010. The total net loss for the second quarter improved to approximately $0.3 million, or $0.01 per share, compared to $10.8 million, or $1.03 per share, for the second quarter of 2009. The total net loss for the first six months of 2010 was $8.1 million, or $0.27 per share, compared to $21.1 million, or $2.03 per share, for the first six months of 2009. The decrease in the net loss in 2010 is primarily a result of the award of approximately $4.1 million to GTC from LEO Pharma, of which approximately a $3.8 million gain was recorded to other income, as well as the recognition of deferred revenue of approximately $4.4 million in connection with the International Chamber of Commerce (ICC) arbitration proceedings.

“We recently announced that GTC is focused on achieving key goals related to Factor VIIa, ATryn^® and our ‘bio-superior’ product candidates. I am pleased to report that the Company made good progress towards achieving these goals during the second quarter,” stated William K. Heiden, Chairman, President and CEO of GTC Biotherapeutics. “Of particular importance was the progress made in preparation for initiation of the Phase I study for rhFVIIa with our partner LFB, which is on track for initiation in the fourth quarter of 2010. As well, we have made progress towards our goal of improving the profitability of ATryn, with the recently announced return of U.S. marketing rights to GTC from Lundbeck Inc., a wholly owned subsidiary of H. Lundbeck A/S in Denmark (Copenhagen Stock Exchange: LUN).”

Program Updates:

Factor VIIa

GTC, together with its collaboration partner LFB Biotechnologies, has established the transgenic rabbit production system for its recombinant form of human coagulation factor VIIa (rhFVIIa) which is being developed for the treatment of patients with hemophilia. Pre-clinical work is on-going in the preparation to initiate a Phase I study in the fourth quarter of 2010. This is planned to be a safety, pharmacokinetic and pharmacodynamic study of rhFVIIa in comparison with NovoSeven^®, in normal healthy volunteers. On the basis of current plans, GTC expects to have results from this study in early 2011.

ATryn^®

On July 16, 2010 GTC announced that it had regained the U.S. commercialization rights to ATryn^® from Lundbeck Inc. There will be a transition period of up to six months wherein Lundbeck will perform certain services on behalf of GTC in order to ensure that ATryn^® will continue to be available to physicians and their patients in an uninterrupted fashion as commercialization responsibilities are smoothly transitioned to GTC. Thereafter, Lundbeck will earn a royalty on net sales beginning in two years, with a predefined cumulative maximum.

In Europe, GTC is in discussions with potential partners for the commercialization and further development of ATryn^®.

Bio-Superiors program (monoclonal antibodies and recombinant forms of plasma derived therapeutic proteins)

Beyond ATryn^®, GTC is developing a portfolio of bio-superior, recombinant forms of human plasma proteins with known therapeutic benefits. GTC has also developed a portfolio of monoclonal antibodies (MAbs) targeting HER2, EGFR and TNF, which address markets with total sales in excess of $16 billion, as well as a CD20 antibody with enhanced ADCC (antibody-dependent cell-mediated cytotoxicity). For example, GTC has established a transgenic goat production system for the production of TG20, a MAb that targets CD20. TG20, which is not identical to rituximab (Rituxan^®), has demonstrated in in-vitro studies that it has an approximately 10-fold greater antibody dependent cell-mediated cytotoxicity, referred to as ADCC, than rituximab. This may translate into improved efficacy or reduced dosage in hematologic malignancies. GTC has established production animals which express trastuzumab (Herceptin^®) in their milk, and this protein is currently being characterized. GTC is also developing transgenic animals for the production of adalimumab (Humira^®) and cetuximab (Erbitux^®). GTC will be seeking partners to support further clinical development and commercialization for these programs.

Other Financial Results

Revenues were approximately $4.9 million for the current quarter, compared to approximately $0.7 million for the second quarter of 2009. Revenues were approximately $5.3 million for the first six months of 2010 compared to approximately $0.9 million for the first six months of 2009, an increase of approximately $4.4 million. The revenue increases in 2010 were primarily from approximately $4.4 million of previously deferred revenue related to our agreement with LEO Pharma. We recognized this revenue once we received a favorable award in the ICC arbitration proceedings at the end of the second quarter.

Costs of revenue and operating expenses were approximately $8.5 million for the current quarter, compared to approximately $10.3 million for the second quarter of 2009, a decrease of 18% year-over-year. Costs of revenue and operating expenses were approximately $16 million for the first half of 2010, approximately 20% lower than $20.1 million for the first half of 2009. The lower expenses in 2010 were primarily due to decreased costs on the ATryn^® program.

The reductions in force that GTC implemented in the fourth quarter of 2009 and the second quarter of 2010, together with other expense reductions, are expected to produce expense savings of approximately $13 million to $15 million per year on an annualized basis.

Research and development expenses were $5.2 million for the current quarter compared to $6.8 million for the second quarter of 2009. Research and development expenses were approximately $9.9 million for the first half of 2010 compared to $13.8 million for the first half of 2009. The decrease in research and development expense occurred despite a $1.7 million quarterly increase and a $3.9 million year-to-date increase in spending on our joint development programs with LFB (recombinant factor VIIa, recombinant factor IX, recombinant alpha-1 antitrypsin and CD-20 monoclonal antibody). The quarterly decrease was due to approximately $0.9 million of LFB funding of the joint program expenses in the second quarter of 2010, as well as a decrease of approximately $1.8 million in spending on the ATryn^® program and a net reduction of approximately $0.6 million in other development programs. The yearly decrease was due to approximately $2.8 million of LFB funding on the joint program expenses in the first half of 2010 as well as a decrease of approximately $3.4 million in spending on the ATryn program and a net reduction of approximately $1.6 million in other development programs.

Selling, general and administrative expenses were $2.8 million for the current quarter of 2010, compared to $3.1 million for the second quarter of 2009 and $5.5 million for the first half of 2010, compared to $5.6 million for the first half of 2009. The quarterly decrease in expenses was primarily due to the absence in 2010 of the legal costs associated with the LEO arbitration in 2009.

The weighted average number of shares outstanding increased from 10.4 million shares in the three and six month periods of 2009 to 30.4 million shares in the three and six month periods of 2010. The increase in shares outstanding is due to the financing activities completed in 2009 as well as the conversion by LFB in January 2010 of its remaining holdings of Series E Convertible Preferred Stock into common stock. GTC had approximately 30.4 million common shares outstanding as of July 4, 2010.

Cash Position

Cash at July 4, 2010 totaled $6.2 million, a $2.4 million increase compared to $3.8 million at January 3, 2010. In February 2010, GTC obtained $7 million of new funding from LFB in the form of a 4%, 36-month term loan with a single payment of principal and interest at maturity. In June 2010, GTC obtained $7 million of new funding from LFB in the form of a 4%, 36-month convertible loan with a single payment of principal and interest at maturity. With our current cash position today, which includes the net award from the ICC arbitration proceedings, and anticipated receipts from existing partnering agreements, service contracts and sales of ATryn^®, GTC projects that its cash resources will be sufficient to support its operations to the middle of the fourth quarter of 2010, exclusive of future cash proceeds from any potential new partnering agreements or additional financing arrangements.

Transfer to Over-The-Counter Bulletin Board (OTCBB)

On March 19, 2010, GTC transferred trading in its common stock from the NASDAQ Capital Market to the Over-the-Counter Bulletin Board (“OTCBB”), an electronic quotation service operated by the Financial Industry Regulatory Authority (“FINRA”). The symbol for GTC’s common stock remains GTCB; however, in some systems investors will be required to enter GTCB.OB to obtain a quote.

About GTC Biotherapeutics

GTC Biotherapeutics develops, supplies and commercializes therapeutic proteins produced through transgenic animal technology. ATryn^®, GTC’s recombinant human antithrombin, has been approved for use in the United States and Europe. ATryn^® is the first therapeutic product produced in transgenic animals to be approved anywhere in the world.

In addition to ATryn^®, GTC is developing a portfolio of recombinant human plasma proteins with known therapeutic properties. These proteins include recombinant forms of human coagulation factors VIIa and IX, which are being developed for the treatment of patients with hemophilia, and recombinant alpha-fetoprotein, which is being developed for the treatment of myasthenia gravis and multiple sclerosis.

GTC’s intellectual property includes 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 enable cost effective development of proteins that are difficult to express in traditional recombinant production systems as well as proteins 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 prospects for initiation of clinical studies in the factor VIIa program and for additional indications in the ATryn^® program, as well as projections regarding the impact of cost savings measures and GTC’s projected cash runway. 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, as updated or supplemented from time to time by those risks and uncertainties included in its other periodic reports as filed with the Securities and Exchange Commission, including the risks and uncertainties associated with dependence upon the actions of partners and regulatory agencies, the uncertainties associated with conducting clinical studies, and the uncertainty that GTC will be able to obtain additional financial resources, including through continuing and new external programs and marketing and strategic partners for some of its internal programs and through additional financing arrangements. 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.

ATryn^® is a registered trademark of GTC Biotherapeutics, Inc.

Erbitux^® is a registered trademark of ImClone LLC.

Humira^® is a registered trademark of Abbott Laboratories.

Herceptin^® and Rituxan^® are registered trademarks of Genentech, Inc.

GTC BIOTHERAPEUTICS, INC.

Selected Financial Information

(Unaudited, in thousands except per share amounts)

	Three months ended						Six months ended
	July 4, 2010			June 28, 2009			July 4, 2010			June 28, 2009
Revenues:
Service revenue	$	275		$	461		$	441		$	638
Product revenue		4,650			194			4,830			215
		4,925			655			5,271			853
Costs of revenue and operating expenses:
Cost of service revenue		518			354			526			620
Cost of product revenue		33			16			53			16
Research and development		5,150			6,805			9,918			13,773
Selling, general and administrative		2,750			3,136			5,533			5,645
		8,451			10,311			16,030			20,054
Loss from operations	$	(3,526	)	$	(9,656	)	$	(10,759	)	$	(19,201	)
Other income (expense):		3,214			(1,101	)		2,700			(1,910	)
Net Loss	$	(312	)	$	(10,757	)	$	(8,059	)	$	(21,111	)
Net loss per common share (basic and diluted)	$	(0.01	)	$	(1.03	)	$	(0.27	)	$	(2.03	)
Weighted average number of shares outstanding (basic and diluted)		30,434			10,440			30,365			10,424
	July 4, 2010			January 3, 2010
Cash and marketable securities	$	6,220		$	3,816
Other current assets		2,733			3,615
Other receivable - arbitration award		4,032			—
Property and equipment, (net)		11,837			12,456
Other assets		5,566			6,113
Total assets	$	30,388		$	26,000
Current liabilities	$	16,226		$	16,641
Short-term deferred contract revenue		10,353			6,875
Long-term deferred contract revenue		—			8,173
Long-term debt		31,147			16,758
Other liabilities		20			37
Shareholders’ deficit		(27,358	)		(22,484	)
Total liabilities and shareholders’ deficit	$	30,388		$	26,000