The relationships among penile segmental pulsatile blood flow, pelvic musculovascular events, phases of nocturnal penile tumescence, and sleep stages were studied by all-night polysomnography in 23 healthy middle-aged men. Penile blood flow peaked during maximal tumescence. Bursts of phasic musculovascular activity were more frequent during ascending and maximal tumescence than during detumescence and baseline. Both penile blood flow and the number of musculovascular events increased during REM sleep. These data describe important local aspects of penile erectile mechanisms in normal men. The findings on musculovascular events support the notion that the bulbocavernosus-ischiocavernosus muscles have a role in human penile erection.