The discovery of effective therapies for HIV requires a fundamental knowledge of retroviral infections. Research by the Public Health Service and collaborating organizations on oncogenic viruses, including retroviruses, has provided much of the basic understanding of retroviruses in general and anti-retroviral therapies in particular. Early work by the National Cancer Institute and the National Institute of Allergy and Infectious Disease also contributed much to an understanding of AIDS and its treatment. Additional research programs have focused on screening compounds for activity against HIV; designing new therapies based on immunologic, biologic, synthetic, and comprehensive approaches to treatment; and testing potential agents in controlled clinical trials. As a result of these activities, researchers have identified one drug, azidothymidine, that has proven effective in prolonging the lives of some AIDS patients. A variety of other promising drugs are currently undergoing clinical trials, including anti-HIV therapies, therapies for the opportunistic infections associated with AIDS, biological response modifiers, and therapies for AIDS-associated malignancies. 15 references (Author abstract modified)