Penile erection is a complex neurovascular phenomenon that takes place with the active contribution of arterial and sinusoidal structures. However, some authors claim that larger veins including the deep dorsal veins that produce contractions, might be involved in the physiology of erection. This study was designed to clarify the contractile properties of deep dorsal penile veins (DDPV). The effect of serotonin (5-HT), noradrenaline (NA), adenosine triphosphate (ATP) and acethylcholine (Ach) on the isolated DDPVs of 16 impotent men, 9 with veno-occlusive dysfunction and 7 without venous leakage, and 5 potent men (controls) who underwent radical prostatectomy, were examined in vitro. Although NA, ATP and Ach had no effect, 5-HT produced concentration-dependent contractions. E max and pEC 50 of 5-HT were 411 +/− 10 mg., 5.92 +/− 0.25; 1020 +/− 260 mg., 5.83 +/− 0.24 and 160 +/− 40 mg., 6.4 +/− 0.22 in controls and patients who had venous leakage and no venous leakage, respectively. Samples of controls were contracted only with 5-HT 2 agonist, DOI (pEC 50 = 5.63 +/− 0.02), and these contractions were antagonized with 5-HT 2 antagonist ketanserin. On the other hand, both DOI (pEC 50 = 6.30 +/− 0.77) and 5-HT 1 agonist, 5-CT (pEC 50 = 6.23 +/− 0.21) produced venoconstriction in patients with veno-occlusive dysfunction. The present findings suggest that 5-HT receptor functions in the DDPVs are of 5-HT 2 subtype in potent men and the altered response to 5-HT in patients with veno-occlusive disease may play a role in the pathophysiology of impotence.