In 14 normal male adults and 97 male patients having impotence alone or together with systematic and/or neuro-psychiatric symptoms and signs, the somatosensory cerebral-evoked potentials were obtained by glans penis stimulation (penile SEP); by peroneal nerve stimulation (peroneal SEP) and by electrically-induced bulbocavernous (BC) reflex. In normal subjects, the configurations of both SEPs were basically similar, except that the onset of latency was 10-15 msec longer and the amplitude in the P1-N1 component was higher in penile SEP. BC-reflex latency was abnormally prolonged, especially in diabetic impotence and in patients with cauda/conus lesions, while the abnormalities on the penile and peroneal SEP were more frequent in patients with spinal cord injuries. MS and parkinsonism. In impotent patients with epilepsy, chronic prostatis and psychogenic problems, all the tests were generally normal.