Neurologic manifestations of human immunodeficiency virus (HIV) infection, rather than being a late complication of the disease, are principally correlated with the early central nervous system (CNS) localization of HIV. The CNS may be infected in the early stages of acquired immunodeficiency syndrome (AIDS) without evidence of neurologic disorders. Evoked potentials (visual, auditory, and somatosensory) and electronystagmographic test batteries have proven to be very sensitive in showing subclinical CNS disorders due to HIV. In this study, auditory brain stem response (ABR) and electronystagmographic test battery findings (smooth pursuit, saccades, caloric test) were performed in 29 neurologically asymptomatic, HIV-positive subjects at different stages of the disease. Compared to results of a control group, the ABR latencies of waves V, I, and III and interpeaks I-V and III-V were significantly increased in HIV patients. The same parameters did not differ significantly among the stages of the disease. In HIV-positive subjects, the accuracy of saccades was significantly reduced, while latency was normal. The velocity and the gain of pursuit were significantly reduced in HIV-positive patients, and 15 of 29 patients showed corrective saccades. Caloric tests revealed qualitative nystagmus abnormalities in 82% of HIV patients, while quantitative parameters were normal. The present results confirm that CNS involvement by HIV occurs early in the course of the disease. In particular, HIV does not seem to affect the labyrinth or the eighth cranial nerve, as demonstrated by the normality of the I-III value of the ABR and of the quantitative parameters of the caloric responses, but it does appear to involve the brain stem acoustic pathways, pontocerebellar pathways, and supratentorial areas.