Seventy-eight asymptomatic HIV-seropositive (aHIV) subjects were examined by means of an extensive neuropsychological test battery in comparison with 32 HIV-seronegative controls. They were also tested with regard to CD4+ and serum p24 antigen. Fifty-six of them completed a clinical follow-up of 12 up to 36 months and 35 also underwent a second session of neuropsychological, CD4+ and p24 antigen assessments at a 12- to 18-month interval from the first session. Results obtained lead to the following conclusions: (a) even among aHIV subjects there is a significant prevalence (28.2%) of cognitive abnormalities for which no cause other than HIV can be found, and therefore this suggests the possible development of HIV-related brain damage since the earliest stages of infection; (b) most sensitive to early HIV-related cognitive impairment are timed psychomotor tasks and memory tasks which require attention, learning and 'active' monitoring or retrieval of information; (c) during the early asymptomatic stages of HIV infection, there is no clear-cut evidence of a cross-sectional relationship between cognition and immunological/ virological markers (at least in the high ranges of CD4+ cell counts considered here); only in relatively more advanced stages does this relationship become evident in the subgroup of aHIV subjects with cognitive abnormalities; (d) the presence of cognitive abnormalities in early HIV infection is predictive of a further decrease in cognitive functioning and faster progression to AIDS-this latter reflected by a faster rate of decline in the number of CD4+ cells and by an increase in positivity of serum p24 antigen.