A total of 108 asymptomatic Western blot (WB)+, 53 EIA+/WB-, and 3 EIA+/WB indeterminate donors have been enrolled in a 5- year prospective study. The source of HIV exposure was homosexual activity, 70% (83% of males); heterosexual contact, 22% (100% of females); IV drugs, 3%; transfusion, 1%; unknown, 4%. Compared with the WB- controls, WB+ donors were more frequently black (56 vs 6%), male (85 vs 51%), and young (mean age 32 vs 40). The ratio of high to low risk WB+ donors decreased from 5:1 to 1:1 during the first 20 months of the study. On initial evaluation, WB+ donors were significantly more likely than WB- donors to have T4 cells less than 400/uL (45 vs 6%, predictive value (PV) = 93.5%), T4/T8 ratio less than 0.8 (70 vs 2%, PV=98.5%), IgG less than 1.8 g/dL (48 vs 2%, PV = 98%), and positive anti-HBc (55 vs 2%, PV=98.2%). Diminished responses to tetanus, PWM, and PHA were seen in 45, 35, and 22% of WB+, vs 9, 8, and 5% of WB- donors. By 1 yr. of follow-up, 14% of WB+ individuals had abnormal responses to all 3 mitogens; by 18 mos, 16% had T4 less than 100/uL and 20% had T4 less than 0.2. HIV was isolated from 23 of 108 (21%) WB+ donors on at least one visit. Sixty-three percent of WB+ donors were initially in CDC group II; 22 of 66 (33%) of these subsequently developed lymphadenopathy. Seven of 108 (6%) progressed to CDC IV; 3 developed thrush, 2 pneumocystis, 1 tuberculosis, and 1 constitutional disease. None of 56 EIA+/WB- or indeterminate donors were in HIV risk groups and none had evidence of HIV-related immune dysfunction or positive viral cultures.