Santa Clara, California
July 23, 2003

Affymetrix, Inc., (Nasdaq: AFFX - News) today announced the broad availability of two new GeneChip® brand products for DNA analysis: the Mapping 10K Array for whole genome SNP analysis and the CustomSeq(TM) Resequencing Array for large-scale, custom resequencing projects. The products were successfully tested by nearly 50 early access customers during the past nine months in a variety of applications, including genetic linkage analysis, mitochondrial genome resequencing and cancer cell genotyping.

"Using the Mapping 10K we found a disease locus in a week's time," said Dr. Peter Nuernberg, Director of the Gene Mapping Center at the Max-Delbruck Center in Berlin. "With conventional microsatellite analysis this usually takes several months. The Mapping 10K array technology is superior to microsatellites and will change the way we do genetic linkage analysis."

"In less than two weeks, I completely resequenced 20 mitochondrial genomes using CustomSeq arrays," said Dr. Anirban Maitra, Assistant Professor of Medicine, Johns Hopkins University. "I used only three PCR amplifications, dramatically simplifying the sample prep required. Data analysis proved to be faster and more accurate than with capillary sequencing. By enabling the individual researchers to conduct large-scale sequencing experiments in their own labs, CustomSeq arrays will facilitate the adoption of complete sequence analysis for clinical applications."

Affymetrix DNA analysis products use 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 Mapping 10K Array and CustomSeq(TM) Resequencing Array bring more information to the benchtop, creating an opportunity for both individuals and institutions to conduct large-scale research.

"These new product lines meet the growing customer demand for powerful SNP genotyping and resequencing solutions in basic research, clinical research and development, drug discovery, and pharmacogenomics," said Greg Yap, Affymetrix' Senior Marketing Director, DNA Analysis. "High-resolution DNA analysis tools like these will give customers richer information and clearer insights, leading to better decisions."

Mapping 10K Array

The Mapping 10K Array brings whole genome SNP analysis to the benchtop by combining an innovative, scalable assay with a proven information platform -- 1 primer, 1 array, 10,000 SNPs. The Mapping 10K delivers the most markers and highest resolution available in a single experiment, making it easier to pinpoint genomic regions linked to disease. The Mapping 10K's innovative assay does not require thousands of individual primers or multiplex PCR, enabling researchers to analyze 10,000 SNPs with a single primer pair. The assay uses only 250 ng of DNA -- far less than conventional methods. Genotype calling is automatic and highly accurate, as measured by more than 99.5 percent concordance with other methods and more than 99.9 percent reproducibility. Applications include genetic linkage studies of inherited disease in families, cancer genetics, and population genetics.

Some early customers have already conducted large studies using the Mapping 10K, such as Novartis, which recently completed a study of over 500 individuals in two weeks producing over 5 million genotypes.

"With the new GeneChip Mapping 10K, Affymetrix now offers the most comprehensive technology available for whole genome scans," said Christian Lavedan, Director of the Pharmacogenomics Laboratory at Novartis. "The assay is amenable to high throughput genotyping analysis. The Mapping 10K is the first product to allow customers to map blocks of linkage disequilibrium (LD) at such high density over the entire genome. Using this tool, we have found that there are multiple blocks of extensive LD across the genome. You do not need a marker every 5 kb to start doing these experiments. Ten thousand SNPs provide sufficient resolution to examine a large portion of the genome for association studies."

"The Mapping 10K Array allowed us to genotype cancer cells much faster than before and at the same time detect chromosomal copy number changes, including loss of heterozygosity (LOH), amplification, and deletion, at greater resolution than previously available," said Dr. Richard Wooster, Senior Investigator, Wellcome Trust Sanger Institute. "This will rapidly advance our understanding of the genetic changes that arise during the development of cancer."

CustomSeq Resequencing Array

The CustomSeq Resequencing Array can sequence and genotype 30,000 base pairs in just two days. Researchers can choose any sequence, including either long regions or different combinations of genes. Overall accuracy is greater than 99.99 percent. Completed sequence across both strands (30,000 bases each strand) is delivered automatically with minimal assembly and sequence alignment, making high-throughput resequencing accessible to every researcher.

Applications for CustomSeq arrays include pathogen resequencing and subtyping, mitochondrial sequence analysis, and SNP discovery.

For more information about Affymetrix DNA analysis products, including the Mapping 10K Array for whole genome scanning and the CustomSeq Resequencing Array for comparative sequencing, visit www.affymetrix.com, or contact your local Affymetrix representative.

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 www.affymetrix.com.

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