In some patients nocturnal penile tumescence (NPT) is abnormal, while the others diagnostic evaluations and medical history do not indicate any specific organic cause of impotence. Aim of this study was to evaluate heart rate variability during sleep in impotent patients with any demonstrable organic cause of impotence. We studied 50 patients: 26 were psychogenic and 24 organic on the basis of NPT and nocturnal rigidity. A lower orthosympathetic activity has been found in organic patients. Because beta-adrenergic receptors mediate relaxation of corpus cavernosum, it could be hypothesized a penile beta-adrenergic dysfunction in our organic patients.