Assessment of neurobehavioral and peripheral neurologic performance among homosexual men was made on two occasions, using a computer-administered neurobehavioral instrument and quantitative vibration threshold testing, respectively. Persons studied included high-risk human immunodeficiency virus (HIV)-negative men (n = 13), asymptomatic HIV-positive men (n = 30), and patients with acquired immunodeficiency syndrome (AIDS)-related complex of AIDS (n = 17). In addition, subjects were characterized immunologically at the time of neurologic and neuropsychologic assessment via determination of circulating lymphocyte counts (total lymphocytes, helper T cells, suppressor T cells, total T cells, activated T cells) and markers of HIV type 1 (HIV-1) infection. At the first cycle of testing, the results of asymptomatic HIV-positive men were indistinguishable from those of HIV-negative men, while persons with AIDS-related complex or AIDS tended to have lower mean performance. These differences did not achieve statistical significance on any single test, but the group with AIDS-related complex or AIDS had the worst mean performance on 12 of 13 individual performance tests. Thirty-seven men underwent repeated testing after a mean interval of approximately 4.5 months. There was little change in mean neurobehavioral performance and vibratory thresholds among all three groups. Measures of neurobehavioral performance and vibrotactile thresholds were not correlated with measures of immunological status. These results are consistent with the concept that asymptomatic infection with HIV-1 does not imply the presence of measurable or significant neurologic or neurobehavioral impairment.