To study the natural history of HIV-1 infection in relation to serological and immunological profiles, 199 asymptomatic HIV-1-antibody (HIV-1-core-antibody)-seropositive and 76 seroconverted homosexual men were followed prospectively for 39 months. AIDS was diagnosed in 38 men. The AIDS attack rate was 20.8% after 39 months. The AIDS attack rate in the HIV-I-core-antibody positives was 12.1, versus 30.1% in the HIV-1-core-antibody negatives (P less than 0.001), and it was 13.3% in the HIV-1-antigen (HIV-1-Ag) negatives versus 53.9% in the HIV-1-Ag positives (P less than 0.001). The AIDS attack rate after 39 months was 10.9% in men with counts greater than or equal to 0.5 x 10(9)/l and 49.9% in those with CD4+ lymphocyte counts less than 0.5 x 10(9)/l. AIDS attack rates after 30 months in the same cohort have been previously reported [1], and were as follows: 6.8% in the core-antibody positives versus 35.7% in the core-antibody negatives. 6.9% in the HIV-1-Ag negatives versus 43.9% in the HIV-1-Ag positives, and 6.1% in those with CD4+ lymphocyte counts greater than or equal to 0.5 versus 51.9% in those with CD4+ lymphocyte counts less than 0.5 x 10(9)/l. The disappearance of core antibody, the appearance of antigen and the occurrence of low CD4+ lymphocyte counts preceded AIDS by a mean (s.d.) of 21.3 (8.9), 17.7 (8.8) and 15.7 (8.9) months, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)