GeneChip(R) CustomExpress(TM) 11-Micron Array Format Sets New Standard for Data Capacity: 61,000 Transcripts on a Single Array

By shrinking the features from 18- to 11-microns, Affymetrix is able to put up to 1.3 million features on the new CustomExpress arrays, potentially providing researchers with significant savings in processing and analysis time. This tremendous jump in data capacity was made possible in part by the Affymetrix GeneChip(R) Scanner 3000, which is capable of scanning the higher density 11-micron feature size.

"Our study required an extremely high-density custom array and Affymetrix offered the only one that met our specifications," said Joseph Ecker, Ph.D., Director of the Salk Institute's Genome Analysis Laboratory and early access user of the new higher density arrays. "One factor was reducing the sheer number of arrays we had to use for a single experiment. Other systems we looked at would have required up to 500 arrays, each with 20,000 spots. However, with the Affymetrix custom arrays, we needed just 12 chips, each with 832,000 features."

The CustomExpress array's huge data capacity also enables researchers to do experiments on a single array that previously could only be done using multiple arrays. For example, researchers can now easily study very complex genomes, such as wheat or rice, on a single CustomExpress array, or combine smaller genomes, such as mosquito and malaria, onto a single array.

"Being able to put so much information on just a single array meant we ran 50 arrays instead of 100, cutting our array processing time in half," said John Walker, Ph.D., RNA Dynamics Group Leader at the Genomics Institute of the Novartis Research Foundation. "In addition, being able to put everything on a single chip made the whole process really seamless; the results were very clean."

The foundation of Affymetrix' unrivaled data quality is the use of multiple data points per transcript measurement to provide the most accurate, consistent, and statistically significant dataset possible. Because the CustomExpress array has such large data capacity, researchers don't have to sacrifice data quality for data quantity. Like most GeneChip expression arrays, the CustomExpress probe set uses 22 independent measurements of hybridization for each of the 61,000 transcripts to provide optimal sensitivity and specificity.

"This launch is a major milestone for array technology," said Elizabeth Kerr, Ph.D., Senior Director of Gene Expression Marketing at Affymetrix. "Major innovations in scanner design and array manufacturing technology have enabled us to deliver arrays with nearly three times more content than ever before. Combining this with our powerful probe set strategy provides the necessary flexibility and performance to meet the needs of genomics researchers throughout the life sciences."

This additional new data capacity dramatically increases the flexibility of the CustomExpress offering; scientists can now design their own GeneChip expression arrays using 520 to 61,000 transcripts. The new 11-micron design adds nine additional array formats to the CustomExpress array program.

All CustomExpress arrays are produced using the same high-quality design and photolithographic manufacturing technologies as Affymetrix GeneChip catalog expression arrays to ensure consistent, reproducible results when comparing data from different experiments or labs.

More information on designing CustomExpress arrays may be found on the Affymetrix website -- http://www.affymetrix.com/.

About Affymetrix:

Affymetrix is a pioneer in creating breakthrough tools that are driving the genomic revolution. By applying the principles of semiconductor technology to the life sciences, Affymetrix develops and commercializes systems that enable scientists to improve the quality of life. The Company's customers include pharmaceutical, biotechnology, agrichemical, diagnostics and consumer products companies as well as academic, government and other non-profit research institutes. Affymetrix offers an expanding portfolio of integrated products and services, including its integrated GeneChip platform, to address growing markets focused on understanding the relationship between genes and human health. Additional information on Affymetrix can be found at http://www.affymetrix.com/.

All statements in this press release that are not historical are "forward- looking statements" within the meaning of Section 21E of the Securities Exchange Act as amended, including statements regarding Affymetrix' "expectations," "beliefs," "hopes," "intentions," "strategies" or the like. Such statements are subject to risks and uncertainties that could cause actual results to differ materially for Affymetrix from those projected, including, but not limited to risks of the Company's ability to achieve and sustain higher levels of revenue, higher gross margins, reduced operating expenses, uncertainties relating to technological approaches, manufacturing, product development, market acceptance (including uncertainties relating to product development and market acceptance of the GeneChip CustomExpress 11-micron array format), personnel retention, uncertainties related to cost and pricing of Affymetrix products, dependence on collaborative partners, uncertainties relating to sole source suppliers, uncertainties relating to FDA and other regulatory approvals, competition, risks relating to intellectual property of others and the uncertainties of patent protection and litigation. These and other risk factors are discussed in Affymetrix' Form 10-K for the year ended December 31, 2002 and other SEC reports, including its Quarterly Reports on Form 10-Q for subsequent quarterly periods. Affymetrix expressly disclaims any obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in Affymetrix' expectations with regard thereto or any change in events, conditions, or circumstances on which any such statements are based.

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