In a series of 646 heroin addicts anti-HIV was detected in 428 (66.2%) and HBsAg in 53 (8.2%). Forty-eight (90.5%) of the latter had concomitant chronic HDV infection. Markers of past HBV infection were found in 481 (74.4%). The prevalence of anti-HIV was significantly higher in the 534 subjects with HBV markers than in the other 112 without markers (69.8% versus 49.1%, p less than 0.001). Of the 266 anti-HIV positive subjects followed for 3-48 months (median 12), nine progressed from no disease to persistent generalized lymphadenopathy (PGL), 52 from PGL to AIDS-related complex (ARC) or AIDS (30 and 22 cases respectively), and six from ARC to AIDS. Baseline T4 + cell count was significantly lower and reduction during follow-up significantly greater in heroin addicts with disease progression than in those without.