AN ESTIMATED 16 000 people in the United States will develop acquired immunodeficiency syndrome (AIDS) in 1986.1 Already, an estimated 0.5 to 1.7 million people in the United States have been infected with the human immunodeficiency virus (HIV) (also known as the human T-cell lymphotropic virus type III [HTLV-III] and the lymphadenopathy-associated virus [LAV]).1-3 Blood donor deferral, HIV-antibody screening, and heat treatment of factor concentrates will largely prevent further transmission of HIV to recipients of these products, but blood recipients represent only 2% to 3% of all AIDS cases.1 Sexual contact has been the route of transmission of the virus in over 78% of all AIDS cases. Moreover, the prevalence of infection with HIV is already almost 70% in at least one group of sexually active gay men.4 In the absence of a vaccine or therapy, the major hope for preventing transmission is the adoption of