The sacral spinal cord is one of the main sites of integration of bladder and anal sphincter and sexual function. Clinical tests (bulbocavernous reflex, perineal reflexes) are often inadequate and urodynamic investigations (cystomanometry, urecholine test, Susset's test) are sometimes unhelpful. The integrity of this structure is essential for normal sphincter function and disease at this level (or of its afferent or efferent limbs) produces a peripheral type of disorder. Sacral evoked potentials are an electrophysiological means of testing the bulbocavernous reflex by external stimulation of the dorsal nerve of the penis or clitoris and recording by a needle bipolar electrode in the striated muscle of the sphincter or the bulbocavernous muscle. An objective study of the sacral reflex are (S2, S3, S4) can thus be performed. One hundred and ten patients have undergone this investigation. Normal latency established in a series of 26 healthy volunteers was less than 42.1 ms. Prolongation of this interval is a sign of disease of the reflex are and correlated with urinary or sexual problems in 46 cases of clinical or electrical peripheral neuropathy. The reflex time was normal in all patients with CNS disease (32 cases) and an impotence of psychological origin (6 cases).