News Release

Maxygen subsidiary Verdia announces discovery and improvement of glyphosate tolerance gene

Results published in Science

Peer-Reviewed Publication

Maxygen, Inc.

Redwood City, Calif. – May 20, 2004 – Verdia Inc., a wholly owned subsidiary of Maxygen, Inc. (Nasdaq: MAXY), announced today the publication in the journal Science of a study that describes the successful development of a novel glyphosate-resistant crop trait by scientists at Verdia and Pioneer Hi-Bred International, Inc., a wholly owned subsidiary of DuPont (NYSE: DD). The report details the use of Maxygen's MolecularBreedingTM directed evolution platform to develop enzymes exhibiting glyphosate N-acetyltransferase (GAT) activity that confer glyphosate tolerance to plants. This improvement in enzyme activity may provide an alternative strategy for supporting glyphosate use on major crops such as corn, soybean and cotton.

The study, entitled "Discovery and Directed Evolution of a Glyphosate Tolerance Gene," was performed by Verdia under the direction of Linda Castle, Ph.D., Product Development Group Leader at Verdia and senior author on the study. The study will be featured in the May 21, 2004 issue of Science.

Glyphosate is one of the most commonly used herbicides on many food and non-food crops. The value and importance of glyphosate stems from its effectiveness, low cost and low environmental impact. In 2002, the annual worldwide sales of glyphosate totaled $3.4 billion and global sales of herbicide-tolerant seed and traits was $2.2 billion according to Cropnosis Limited.

Scientists at Verdia used microbial diversity collections to discover a family of genes, called gat genes, exhibiting a very low level of the desired novel enzymatic activity. This activity was then improved using the MolecularBreedingTM directed evolution platform. Eleven iterations of DNAShufflingTM recombination resulted in nearly a 10,000 fold improvement in enzyme activity over the parental enzymes. The ability to improve enzyme activity using the MolecularBreedingTM directed evolution platform outpaced and outperformed traditional means to modify genes and proteins that typically attempt to predict sequence-function relations.

"The increase in activity would never have been possible to achieve using traditional technologies to improve genes such as random mutagenesis and rational design," said Linda Castle, Ph.D. "This demonstration of improved glyphosate tolerance should be applicable to many crops. Further, this study validates our ability to create novel commercial opportunities in crop protection and plant quality traits for ourselves and our partners."

"I am extremely proud of the scientific accomplishments that Maxygen and Verdia have made," said Russell Howard, Ph.D., Chief Executive Officer of Maxygen. "Our MolecularBreedingTM directed evolution platform continues to deliver success in creating valuable commercial properties in genes and proteins for novel business applications."

About Verdia
Verdia is dedicated to becoming a global leader in providing proprietary product solutions to important commercial problems in plant-based businesses through the application of advanced trait optimization methods. Verdia has validated the use of the MolecularBreedingTM directed evolution platform in agriculture through its strategic alliances with industry leaders, including Pioneer Hi-Bred, Syngenta and Delta & Pine Land Company. In addition to the product candidates in development with its partners, Verdia has a pipeline of over 10 potential agriculture products in various stages of development.

About Maxygen
Maxygen, Inc., headquartered in Redwood City, California, is focused on creating novel products using its integrated proprietary technologies for human therapeutics and industrial applications. Maxygen's technologies bring together advances in molecular biology and protein modification to create novel biotechnology products.

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This news release contains forward-looking statements about the research and business prospects of Maxygen and Verdia, including those relating to: Verdia's ability to become a leader in developing transgenic plant products; Maxygen's human therapeutics focus; and the utility of Verdia's proprietary glyphosate-resistant gene to develop commercial agricultural products. Among other things these risks and uncertainties include, but are not limited to: competitors creating superior products; the inherent risks of biological research; Verdia's ability to enter into and/or maintain collaborations and joint ventures; public acceptance of genetically-modified products; and inability to adequately protect from, and defend against, intellectual property claims. These and other risk factors are more fully discussed in Maxygen's Form 10-K for the year ended December 31, 2003, including under the caption "Risk Factors," and in Maxygen's other periodic SEC reports, all of which are available from Maxygen at www.maxygen.com. Maxygen and Verdia disclaim any obligation to update or revise any forward-looking statement contained in this release as a result of new information or future events or developments. Maxygen and MolecularBreeding are trademarks of Maxygen. Verdia is a trademark of Verdia.


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