Affymetrix Inc. (Nasdaq:AFFX) today announced that Pathwork Diagnostics Inc. will begin offering a molecular diagnostic test based on the Affymetrix microarray platform. The Pathwork Tissue of Origin Test is one of the first microarray-based diagnostic tests for cancer in the United States. The test is being made available through the recently CLIA-certified Pathwork® Diagnostics Laboratory.

There are an estimated 200,000 patients with uncertain primary tumors, including Cancer of Unknown Primary, in the U.S. each year.1,2,3 One study concluded that in particularly challenging cases, the primary tumor site is identified only 25 percent of the time using traditional diagnostic tools.4 The Pathwork Tissue of Origin Test is designed to help oncologists determine the primary site of a metastatic tumor with greater certainty.

“The Affymetrix technology enabled us to develop a test that uses the power of genomic information to aid in the diagnosis of uncertain tumors,” said Deborah J. Neff, president and chief executive officer of Pathwork Diagnostics. “Ultimately, we believe the Pathwork Tissue of Origin Test will improve patient outcomes while saving the healthcare system money. We can now offer the test through our CLIA-certified laboratory and we are actively working with the FDA to obtain clearance that will allow us to also offer a diagnostic kit directly to clinical laboratories.”

“Affymetrix is partnering with innovative molecular diagnostic companies like Pathwork Diagnostics to bring about new diagnostic tests that can provide more efficient and complete methods to better diagnose, classify and manage complex diseases like cancer,” said Kevin King, president of Affymetrix. “Affymetrix offers the only microarray instrumentation system that has been cleared for molecular diagnostic laboratories in the U.S. and E.U., and we continue to work with our partners to further facilitate this broad adoption of array-based diagnostic tests and help make personalized medicine a reality.”

Affymetrix is the only company to offer a continuous path to discover, develop and commercialize complex biomarker signature assays. The company partners with the leading diagnostic companies through its Powered by Affymetrix™ (PbA) program. The Affymetrix GeneChip® System 3000Dx is the only microarray instrumentation platform to receive regulatory clearance by the U.S. FDA and to be CE marked in the European Union for in vitro diagnostic use. The CLIA-certified Affymetrix Clinical Services Laboratory (ACSL) offers microarray-based molecular diagnostic patient and clinical trial testing services that enable customers to leverage Affymetrix’ technology and experience to bring more effective molecular diagnostic tests to patients faster than ever before. There are currently more than 20 different molecular assay tests based on the Affymetrix platform under development by Affymetrix and its 11 PbA Partners.

About Affymetrix

Affymetrix GeneChip®microarray technology is the industry-standard tool for analyzing complex genetic information. After inventing microarray technology in the late 1980s, Affymetrix scientists have been dedicated to developing innovative products that provide researchers with a more complete view of the genome. These products continue to accelerate genetic research and enable scientists to develop diagnostics and tailor treatments for individual patients by identifying and measuring the genetic information associated with complex diseases.

Today, Affymetrix technology is used by the world’s top pharmaceutical, diagnostic and biotechnology companies, as well as leading academic, government and not-for-profit research institutes. More than 1,700 systems have been shipped around the world and more than 12,000 peer-reviewed papers have been published using the technology.

Affymetrix is headquartered in Santa Clara, Calif., and has manufacturing facilities in Sacramento, Calif., Cleveland, Ohio, and Singapore. The company has about 1,100 employees worldwide and maintains sales and distribution operations across Europe and Asia. For more information about Affymetrix, please visit the company’s website at www.affymetrix.com.

Forward-looking Statements

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 and uncertainties relating to commercial success of the agreement with Pathwork® Diagnostics Tissue of Origin Test discussed in this press release; risks of the company’s ability to achieve and sustain higher levels of revenue, higher gross margins and reduced operating expenses; uncertainties related to technological approaches, manufacturing and product development; personnel retention; uncertainties related to cost and pricing of Affymetrix products; dependence on collaborative partners; uncertainties related to sole-source suppliers; risks associated with past and future acquisitions; 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, 2007, 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.

1 Pavlidis N, Fizazi K. Cancer of Unknown Primary (CUP). Critical Reviews in Oncology/Hematology. 2005;54:243-250.

2 Tong KB, Murtagh KN, Hubert HB, et al. Incidence, costs of care and survival of Medicare beneficiaries diagnosed with carcinoma of unknown primary (CUP). Poster presented at annual meeting of Association for Molecular Pathology; November 17, 2006; Orlando, FL.

3 Pathwork Diagnostics analysis.

4 Hillen HF. Unknown primary tumours. Postgrad Med J. 2000;76:690-693.