HIV antigenemia was found in 52/243 HIV antibody positive individuals attending 2 AIDS-screening clinics, giving a prevalence of 13, 25 and 76% in CDC groups II, III and IV, respectively. No correlation was found to decreased CD4 lymphocyte values in the individual groups. HIV antigen therefore identified a separate subpopulation. For 138 asymptomatic patients followed prospectively both laboratory parameters predicted HIV-related events, the relative risk factor being 4 for low CD4 value and 6 for presence of HIV antigen. Individuals presenting with HIV antigen and decreased CD4 count all developed disease within 18 months, the relative risk factor being 24. Thus the 2 markers, when measured together, effectively separated asymptomatic HIV-infected patients into 1 of 3 risk categories.