The aim of the study was to clarify the pathophysiologic significance of full but short-lived nocturnal erections observed in some impotent men. Penile circulation was assessed by color Doppler sonography and pharmacocavernosometry in 35 impotent patients who underwent polysomnographic recording of nocturnal erections. In each case, there were at least 3 erectile episodes with a complete rigidity (always > 700 g) but with a short duration (mean duration of the maximum level of full erection = 4 min; always < 6 min). All patients demonstrated a normal arterial inflow with mean +/- SEM right and left cavernosal peak flow velocities of 39.5 +/- 1.8 and 41.3 +/- 1.5 cm/s, respectively. Pharmacocavernosometry detected a dysfunction of the cavernous veno-occlusive mechanism (mean +/- SEM maintenance flow: 45 +/- 8 ml/min and mean +/- SEM corporal pressure decay over 30 s: 82.5 +/- 9 mm Hg) in 18 patients (51%). In these patients, this finding may be a possible explanation for the short duration of nocturnal erectile episodes. In the remaining 17 patients (49%) with normal penile vascular status, a dysfunction of the adrenergic system could play a role in the pathophysiology of this picture. Full but short-lived nocturnal erections, as assessed by polysomnographic recording, are indicative of a normal arterial status and should encourage further assessment of the corporal veno-occlusive mechanism.