SAN DIEGO, CA - (March 27, 2000) - Quest Diagnostics Incorporated (NYSE: DGX), the nation's leading provider of diagnostic testing, information and services, and privately-held Structural Bioinformatics, Inc. (SBI), a world leader in protein modeling, announced today the achievement of several milestones in their structural pharmacogenomics collaboration including new work on HIV-1 Integrase.

At present, there is no way to predict the response rate for drug efficacy prior to clinical trials or to influence the outcome of such trials in a positive manner during the drug discovery and development process. However, by incorporating protein structural knowledge at the drug discovery and design stage, synthesis of drug candidates can be focused toward compounds which will "satisfy" the binding sites of the largest fraction of structural polymorphisms found in the receptor, and thus be likely to have efficacy in the largest possible fraction of the patient population.

Each QSVdBase^TM database module represents a sampling of a specific drug target shape observed in the genetic polymorphisms of the patient population. The protein structure of each drug target is modeled from the genetic sequence variants (polymorphisms) of a single drug target derived from these individuals. These structure data provide a definitive key to understanding differences in interactions between a drug or potential drug and the structural variations of its intended target, which is critical to optimal drug design and the selection of the optimal drug candidate for initiation of human trials.

A structural pharmacogenomics database for HIV-1 Integrase is currently under active development and contains several hundred variant structures. HIV-Integrase is a 31 kD protein produced from the C-terminal portion of the Pol gene product and is responsible for the integration of proviral DNA into the host genome, which is essential for HIV replication. Integrase, therefore, remains a promising potential target for new anti-HIV therapeutics. Foreknowledge of the drug target shape-repertoire found in the patient population will permit identification of structurally conserved regions of the protein as potential sites of interaction for new drugs as well as informed selection of the optimal drug candidate from among the available candidates before initiation of clinical trials.

Significant milestones have been reached in the development of two other modules. The HIV-RT and HIV-PR modules now contain more than 30,000 unique structures (in aggregate) derived from individual patient samples, along with drug resistance data and structures for all currently approved drugs docked into the active site.

The databases are continually updated with the addition of approximately 1,000 sequences/structures per month. The sequence data is generated by Quest Diagnostics' Nichols Institute Laboratory, which is CAP accredited and ISO9001 certified.

Quest Diagnostics is the nation's leading provider of diagnostic testing, information and services to physicians, hospitals, managed care organizations, employers and government agencies with annualized revenues of more than $3 billion. The wide variety of tests performed on human tissue and fluids help doctors and hospitals diagnose, treat and monitor disease. Its Nichols Institute unit conducts research, specializes in esoteric testing using molecular diagnostics and other advanced technologies. Quest Diagnostics is one of the leading providers of testing to support clinical trials of new pharmaceuticals worldwide. Quest Informatics collects and analyzes laboratory, pharmaceutical and other data to help large health care customers better manage the health of their patients. Additional company information can be found on the Internet at: www.questdiagnostics.com.

Structural Bioinformatics is a world leader in computational proteomics - the study of the structural properties of proteins using mathematical algorithms. The Company has developed proprietary algorithms to generate three-dimensional structural models of proteins from primary gene sequence data, and to perform primary drug discovery screening in silico. SBI offers two subscription database products. The first, SBdBase^TM, is composed of thousands of structural models of proteins from more than 150 distinct families and promises to accelerate lead optimization and rational drug design. The second is SVdBase^TM, a series of databases each containing structural models generated from genetic variations in a single, medically important gene, such as HIV-Reverse Transcriptase. These databases will enable better target selection and optimize drug design. SBI is working with Quest Diagnostics, Inc. to develop the HIV SVdBase^TM. SBI also employs its technologies in collaborative R&D programs. Current partners include DuPont Pharmaceuticals Company, BioChem Pharma, Inc. and Yamanouchi Pharmaceutical Co., Ltd.