Fifty-eight HIV-positive drug abusers and 22 HIV-positive nondrug abusers at stages II-III and IV of the Centers for Disease Control classification were evaluated neuropsychologically. The study confirmed previous findings that drug abuse has a negative influence on cognitive function. It also emerges that seropositivity affects cognitive function, although the poor performance of group II-III patients compared to group IV may be explained by factors related to seropositivity (anxiety and panic) rather than the disease itself. It is concluded that disease-related factors probably determine cognitive performance in the earlier stages of HIV infection.