New Affymetrix Arrays with 100,000 SNPs Available for Early Technology Access Customers

First in a family of arrays that will enable genome-wide association studies

Santa Clara, Calif., April 5, 2004 – Affymetrix, Inc., (Nasdaq: AFFX) announced today that its new GeneChip® Mapping 100K Array Set is now broadly available through an early technology access program. This two-microarray set can genotype over 100,000 SNPs and is the first in a family of products that will enable scientists to begin large-scale whole-genome association studies, which up to now have been unaffordable or impractical.

The 100K, which Affymetrix plans to formally launch this summer, is already being used in high-density genome scans and genome-wide association studies of the genetics of complex diseases and drug response. Twelve customers, including leading pharmaceutical and biotechnology companies and leading academic researchers, have started experiments under the initial phase of the program, which is now expanding.

"We were amazed at how quickly we could generate highly accurate genotype calls,” said Dr. Peter Nürnberg, Head of the Gene Mapping Center at the Max Delbruck Center for Molecular Medicine in Berlin-Buch and coordinator of the National Genotyping Platform of Germany. “The 100K is a significant step to allow whole genome association studies. We anticipate the 100K will have a significant impact on our research in the field of complex diseases and beyond."

In a pharmacogenomic study funded by the National Heart, Lung, and Blood Institute, researchers at the Mayo Clinic are using the 100K to investigate the genetic basis for differential responses to antihypertensive drugs in different patients and populations. By taking a whole-genome association approach to these studies, these scientists hope to identify the unknown genes influencing drug-response and to ultimately enable more effective tailoring of antihypertensive therapy in individual patients.

The 100K is the newest member of the Affymetrix DNA analysis product line, which includes comparative sequencing, custom genotyping, and whole genome SNP microarrays. The 100K uses the same GeneChip technology that revolutionized mRNA gene expression analysis, enabling researchers to understand both the function and variation of whole genomes on a single, integrated platform.

The 100K builds on the innovative, scalable, easy to use assay that Affymetrix pioneered with the GeneChip Mapping 10K Array. The 100K allows researchers to genotype over 100,000 SNPs using just two reactions. Previously, genotyping 100,000 SNPs would have required 100,000 PCR reactions, a hurdle that made this kind of research impractical. Before the advent of 100K, the commercial product for genotyping the most SNPs was Affymetrix' Mapping 10K.

“The power of 100,000 SNPs in a single experiment is enabling researchers to attempt unprecedented genetic studies at a genome-wide scale,” said Greg Yap, Sr. Marketing Director, DNA Analysis. “The GeneChip Mapping 100K Set is the first in a family of products that will enable scientists to identify genes associated with disease or drug response across the whole genome instead of just studying previously known SNPs or genes, and to study complex real-world populations instead of simple ones. To do this, we are making large-scale SNP genotyping not only quick and easy, but also affordable -- about 1 cent per SNP.”

About half of the SNPs on the 100K set are from public databases, while the other half are from the SNP database discovered by Perlegen Sciences, Inc. All of the SNPs on the 100K set are freely available and have been released into the public domain. Because the assays and arrays used in the 100K set are extremely scalable, more SNPs from both public sources and the Perlegen database will be added to next generation arrays.

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 brand platform, to address growing markets focused on understanding the relationship between genes and human health. Additional information on Affymetrix can be found at 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® 100K Mapping Array set), 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, 2003 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.

NOTE: Affymetrix, the Affymetrix logo, and GeneChip are registered trademarks owned or used by Affymetrix, Inc.

SOURCE Affymetrix, Inc.

CONTACT: Media Contact: Wes Conard, Associate Director, Public Relations, +1-408-731-5791, or Investor Contact: Doug Farrell, Vice President, Investor Relations, +1-408-731-5285, both of Affymetrix, Inc.