Business Wire - July 10, 2000

Four studies of HIV drug resistance presented here at the XIII International AIDS Conference utilized PhenoSense HIV, the phenotypic drug resistance test developed and marketed by ViroLogic, Inc. (NASDAQ: VLGC). Phenotypic tests such as PhenoSense HIV directly measure the resistance or susceptibility of a patient's HIV to antiviral drugs and help physicians optimize and individualize therapy for HIV patients.

New research presented at the XIII International AIDS Conference and utilizing PhenoSense HIV includes:

"Factors associated with reduced susceptibility to drugs in the current failing antiretroviral regimen." This study, led by Dr. Richard Haubrich of the University of California, San Diego, identified those HIV patients likely to benefit most from drug resistance testing. Using PhenoSense HIV, scientists measured resistance levels among a group of patients with extensive treatment experience. By comparing PhenoSense results with data on the patients' treatment histories, the researchers were able to identify factors likely to lead to multiple drug resistance, including longer treatment experience, prior non-nucleoside reverse transcriptase inhibitor (NNRTI) use, and greater number of protease inhibitors used. In a physician's office, similar phenotypic resistance testing information would be used to tailor a regimen to the resistance profile of an individual patient.

"Prevalence of mutations associated with ART resistance among drug-naive persons recently diagnosed with HIV-1 (1997-1999)," led by Dr. Hillard Weinstock of the U.S. Centers for Disease Control and Prevention, demonstrated evidence of resistance to antiretroviral therapy (ART) in many patients prior to receiving any treatment for HIV infection. The study's findings add to the body of research which indicates that drug-resistant HIV is being transmitted in the U.S.

"Transmission of drug resistant HIV-1 in San Francisco, 1996-1999," led by Dr. Robert Grant of the University of California, San Francisco, found evidence of increasing rates of drug resistance over time to NNRTI and protease inhibitor drugs among individuals recently infected with HIV between 1996 and 1999. In 1999, viruses resistant to NNRTI or PI were identified in 11.5% and 7.7%, respectively, of recently infected individuals. These data suggest that routine screening of newly infected patients for drug resistant HIV is warranted.

"An HIV-1 variant that shows dose-dependent stimulation of replication in the presence of non-nucleoside reverse transcriptase inhibitors," conducted by ViroLogic scientists led by Dr. Jeannette Whitcomb, discovered a novel resistance phenomenon in blood from a single patient. Using PhenoSense HIV, researchers determined that at defined concentrations of an NNRTI, certain strains of HIV could replicate more effectively in the presence of the drug than in its absence. Researchers plan further studies to examine the interaction between HIV and NNRTIs.

About ViroLogic

ViroLogic is a biotechnology company developing and marketing innovative products to guide and improve treatment of viral diseases. The Company's proprietary technology, called PhenoSense(TM), tests for drug resistance and susceptibility in viruses that cause serious diseases such as AIDS, hepatitis B and hepatitis C.

ViroLogic's first product, PhenoSense(TM) HIV, is a test that directly and quantitatively measures resistance of a patient's HIV to antiviral drugs. The test results provide physicians with key information to select appropriate drugs for their HIV patients. The Company is also developing PhenoSense(TM) products for other viral diseases and intends to use the results of its PhenoSense(TM) tests and other clinical data to develop its Therapy Guidance System(TM) (TGS(TM)), an interactive database to help physicians guide patient therapy.

Statements in this press release that are not strictly historical are "forward-looking" statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. These statements involve a high degree of risk and uncertainty that exist in the Company's operations and business environment. Such statements are predictions only and actual events or results may differ materially from those projected in such forward-looking statements. Factors that could affect actual events or results include risks associated with performance under the Company's agreements with third parties, research and development progress, competitive products and the strength of the Company's patent portfolio. These factors and others are more fully described under "Risk Factors" in the Final Prospectus included in the Company's Registration Statement on Form S-1 (File No. 333-30896) as filed with the Securities and Exchange Commission and declared effective by the SEC on May 1, 2000.

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CONTACT: Fenton Communications In Durban, South Africa: Andrew Shih, (27 82) 858-0889 or ViroLogic In the United States: Sidney Ho, 650/635-1100, Ext. 206 Director of Public Affairs sho@virologic.com www.virologic.com
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