We enrolled 253 HIV-antibody positive heroin addicts without HIV-related disease (n = 81) or with persistent generalized lymphadenopathy (n = 172) in a prospective study to evaluate clinical progression to AIDS related complex (ARC) or AIDS and to identify factors of possible prognostic relevance. Follow-up lasted between 6 and 40 months (median 12 months). According to the non-parametric Cox's model the only significant (P less than 0.001) prognostic variable was T4+ cell count considered in three classes: greater than 800/microliters (no depletion), 400-800/microliters (moderate depletion) and less than 400/microliters (absolute depletion). Subjects with T4+ cell count of less than 400/microliters had a risk of developing ARC or AIDS that was 6.46 and 1.98 higher than those with values of greater than 800/microliters or between 400 and 800/microliters respectively. The estimated probability of progression to ARC or AIDS was 0.029, 0.056 and 0.172 at one year in subjects with T4+ cell count of greater than 800/microliters 400-800/microliters and less than 400/microliters, respectively, and 0.296, 0.501, and 0.896 at two years.