Motor weakness and ataxia of lower limbs and abnormalities of somatosensory evoked potentials occur in many patients with the acquired immunodeficiency syndrome (AIDS). We studied 15 human immunodeficiency virus-seropositive subjects without AIDS and found no clinical neurological abnormalities. The mean latency of the brainstem auditory evoked potential (peak V) was increased, suggesting a central defect. Despite normal peripheral nerve conduction along the tibial nerve, the mean latency of the spinal cord potential of the twelfth thoracic vertebra was increased compared with normal, possibly indicating an incipient conduction defect at or near the spinal root ganglion or lumbar spinal cord.