Contacts:	Sharon Tetlow diaDexus (408) 330-5003 stetlow@diadexus.com		Quest Diagnostics Gary Samuels (Media) (201) 393-5700
	Cathy Doherty Investors 201-393-5030

DIADEXUS GRANTS LICENSE TO QUEST DIAGNOSTICS FOR NOVEL GENOMICS-BASED OSTEOPOROSIS DIAGNOSTIC TEST

South San Francisco, CA and Teterboro, NJ - November 21, 2001 - diaDexus, Inc., a privately-held biotechnology company, and Quest Diagnostics Incorporated (NYSE: DGX), the nation's leading provider of gene-based medical testing, announced today that diaDexus has licensed its novel proprietary Cathepsin K genomics-based diagnostic blood test to Quest Diagnostics for the detection and monitoring of osteoporosis.

Quest Diagnostics exercised its option under a previous agreement and has obtained exclusive rights to develop and commercialize the Cathepsin K test in its laboratory facilities in the United States and certain international territories. Under the terms of this license, diaDexus will receive an upfront licensing fee and royalties on future sales, and retain rights to develop a test for certain markets in the future.

Cathepsin K is a protein implicated in the resorption of bone matrix, which is important in the dynamic process of bone remodeling. As a result, Cathepsin K may be used as a marker for osteoporosis, an often debilitating and costly disease. Collaborative studies are planned to confirm the clinical utility of Cathepsin K as a marker for osteoporosis.

Osteoporosis, or porous bone disease, is characterized by low bone mass and structural deterioration of bone tissue, leading to bone fragility and an increased susceptibility to fractures of the hip, spine and wrist. According to the National Osteoporosis Foundation, 10 million individuals have the disease and 18 million more have low bone mass. Approximately 80% of those affected by osteoporosis are women.

About diaDexus
diaDexus, based in South San Francisco, California, is focused on translating genomic sequence data into novel diagnostic and therapeutic products. diaDexus has utilized genomics and bioinformatics to identify thousands of disease-associated molecular targets. Currently diaDexus has three diagnostic product candidates in late-stage pre-clinical development. For more information, please visit www.diadexus.com.

About Quest Diagnostics
Quest Diagnostics is the nation's leading provider of diagnostic testing, information and services with $3.4 billion in annual revenues. The company's diagnostic testing yields information that enables health care professionals and consumers to make better decisions to improve health. Quest Diagnostics offers patients and physicians the broadest access to diagnostic testing services through its national network of approximately 30 full-service laboratories, 150 rapid response laboratories and more than 1,300 patient service centers, where specimens are collected. Quest Diagnostics is the leading provider of esoteric testing, including gene-based testing, and is the leader in routine medical testing, drugs of abuse testing, and non-hospital-based anatomic pathology testing. Quest Diagnostics empowers health care organizations and clinicians with state-of-the-art connectivity solutions that improve practice management. Through partnerships with pharmaceutical, biotechnology and information technology companies, Quest Diagnostics provides support to help speed the development of health care insights and new therapeutics. Additional company information can be found on the Internet at: www.questdiagnostics.com.

The statements in this press release which are not historical facts or information may be forward-looking statements. These forward-looking statements involve risks and uncertainties that could cause the outcome to be materially different. Certain of these risks and uncertainties are listed in the Quest Diagnostics Incorporated 2000 Form 10-K and subsequent filings.