Twenty-five HIV-seropositive drug abusers (DA+HIV+) (groups II-III and IV [A, C2 and E] of the CDC classification) were evaluated by use of the WAIS scale to determine any possible involvement of cognitive functions in the not yet overt phases of AIDS. The results were compared with those obtained in two control populations composed of 19 seronegative drug abusers (DA+HIV-) and 24 healthy subjects (DA-HIV-) to evaluate, in addition to the disease, the possible effect of the use of alcohol and toxic substances on cognitive performance. In spite of the small number of subjects, the study indicated that drug abuse is the main factor, among those analyzed, in determining a decline in cognitive functions.