A group of asymptomatic HIV-infected patients (CDC II and III) was followed-up over a two year period with semi-annual neuropsychological testing. Of the total sample of 36 subjects, all were retested at test two (T2), 19 at test three (T3) and 13 at test four (T4). A subgroup of subjects was further tested on a simple and a complex task of reaction time. The CD4+ and CD8+ lymphocyte counts were measured in peripheral blood. According to our criteria, no patient could be defined as neuropsychologically impaired. A significant improvement in performance was found from T1 to T2 and from T2 to T3, with a leveling off between T3 and T4. No associations were observed between reaction time and changes in neuropsychological test results and immunological parameters. Our results indicate that neuropsychological impairment does not develop gradually in the asymptomatic stages of HIV-infection. Furthermore, measurements of reaction time do not seem to have any prognostic significance neither for neurocognitive function nor for immunological status as measured by us.