Percutaneous magnetic stimulation of the brain and spinal cord is a technique developed to demonstrate early and subclinical abnormalities in corticomotoneuron pathways. Central motor conduction time (CMCT) was evaluated in 58 HIV-seropositive patients neurologically asymptomatic (CDC groups II and III) and in two control groups. CMCT was abnormal in about 50% of HIV-seropositive patients. These electrophysiological abnormalities seem to have a negative prognostic value since about 64% of the patients with abnormal parameters seem to progress more rapidly to AIDS stages.