August 11, 2008

Metabolix Demonstrates Viability of Bioplastic Production in Switchgrass Plants

Metabolix, Inc. (NASDAQ: MBLX) today announced that in recently-completed greenhouse trials, switchgrass plants engineered using Metabolix multi-gene expression technology produced significant amounts of PHA bioplastics in leaf tissues employing Metabolix's expertise in pathway engineering in plants. This result is the first successful expression of a new functional multi-gene pathway in switchgrass, and demonstrates the Company's pathbreaking bioengineering capabilities as a powerful tool for maximizing the potential of biomass crops for both bioplastics and biofuels production.

"Metabolix has been developing technology to produce PHA polymer in switchgrass for over 7 years," said Dr. Oliver Peoples, Chief Scientific Officer. "This result validates the prospect for economic production of PHA polymer in switchgrass, and demonstrates for the first time an important tool for enhancing switchgrass for value-added performance as a bioenergy crop."

Switchgrass is a native prairie grass that can be grown in abundance in the United States. It has been identified by the Department of Energy and the Department of Agriculture as a prime feedstock for producing next generation biofuels and bioproducts. The 2007 Energy Security and Efficiency Act mandated 16 billion gallons of ethanol produced by biomass crops such as switchgrass by the year 2022.

"A key corporate goal has been to develop value-added industrial crops such as oilseeds, sugarcane and switchgrass," said Richard Eno, President and CEO of Metabolix. "This proof of concept in switchgrass is an important milestone as we develop commercialization strategies for our plant science activities."

A detailed scientific paper on the technology entitled "Production of polyhydroxybutyrate in switchgrass, a value-added co-product in an important lignocellulosic biomass crop" was recently accepted for publication in Plant Biotechnology Journal.

About Metabolix

Founded in 1992, Metabolix, Inc. is an innovation driven bioscience company focused on providing sustainable solutions for the world's needs for plastics, chemicals and energy. The Company is taking a systems approach, from gene to end product, integrating sophisticated biotechnology with advanced industrial practice. Metabolix is now developing and commercializing Mirel(TM) bioplastics, a sustainable and biodegradable alternative to petroleum-based plastics. Mirel is suitable for injection molding, extrusion coating, cast film and sheet, blown film and thermoforming. Metabolix is also developing a proprietary platform technology for co-producing plastics, chemicals and energy, from crops such as switchgrass, oilseeds and sugarcane.

Metabolix and Archer Daniels Midland Company (ADM) are commercializing Mirel through a joint venture called Telles. The first commercial scale Mirel production plant is being constructed adjacent to ADM's wet corn mill in Clinton, Iowa. The plant is designed to produce up to 110 million pounds of Mirel annually. Mirel will reduce reliance on petroleum and decrease environmental impacts relative to conventional petroleum-based plastics.

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Safe Harbor for Forward-Looking Statements

This press release contains forward-looking statements which are made pursuant to the safe harbor provisions of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. The forward-looking statements in this release do not constitute guarantees of future performance. Investors are cautioned that statements in this press release which are not strictly historical statements, including, without limitation, statements regarding commercial viability of Mirel and the outcome of the Company's research and development, constitute forward-looking statements. Such forward-looking statements are subject to a number of risks and uncertainties that could cause actual results to differ materially from those anticipated, including, without limitation, risks associated with: the ability of Metabolix and ADM to successfully manufacture Mirel at commercial scale and in a timely and economic manner, the Company's ability to develop and successfully commercialize Mirel, its ability to obtain required regulatory approvals, market acceptance of Metabolix products, the Company's ability to compete with petrochemical-based plastics, chemicals and energy and with other biobased products, the success of its research and development programs, and other risks detailed in Metabolix's filings with the Securities and Exchange Commission, including form 10-K for the year ended December 30, 2007, which was filed on March 13, 2008, and form 10-Q for the quarter ended March 31, 2008, which was filed on May 8, 2008. Metabolix assumes no obligation to update any forward-looking information contained in this press release or with respect to the announcements described herein.