During a field study in the Seychelles Islands, 19 patients with tropical spastic paraparesis (TSP) were evaluated electrophysiologically. Methods of assessment included motor and sensory nerve conduction studies, electromyography, and analysis of the somatosensory evoked potentials after stimulation of the tibial and median nerves. The results showed that the most prominent feature of the disease, a spastic paraparesis, is accompanied by subclinical involvement of spinal sensory pathways and a comparatively minor peripheral sensorimotor polyneuropathy.