Perineal electrophysiological investigations allow an objective and quantitative approach to the different somatic (motor or sensitive) and vegetative nerve pathways involved in the control of erection. The level of neurogenic involvement (central or peripheral, encephalic, spinal, radicular, troncular) can be determined precisely and, sometimes, the prognosis also. A series of 423 patients underwent the following investigations: detection electromyography of the perineal floor muscles and recordings of the bulbo-cavernosus reflex latency, medial pudendal nerve somesthesic cortical evoked potentials, conduction rate of the dorsal nerve of the penis and sympathetic skin response. An alteration in at least one of the tests was observed in 49% of the patients. The most frequently observed disturbance involved reduced sensitive conduction of the dorsal nerve of the penis in neurologic patients (64.5%).