Penile NO release test (PNORT) has been designed to try to evaluate clinically the penile endothelial function (PEF). The shear-stress flow-mediated vasodilation (FMD) of the cavernous arteries is evaluated in two groups of patients with neurogenic (n=23) and vasculogenic (n=23) erectile dysfunction (ED) by measuring their percent of increase after a 5 min occlusion of the flow. Both groups show an important FMD decrease (17.78+/-11.78 and 17.82+/-13%) as compared to the age-matched control group (n=12) (65.14+/-30.5%, P<0.001). In the vasculogenic and control groups, mean FMD is lower in patients with one or more arterial risk factors(41 vs 67%, P=0.025), and show a positive correlation with the plasmatic levels of bioavailable testosterone (r=0.37, P=0.03) and of DHEA-S (r=0.46, P=0.014). Patients achieving full erection at pharmacological test with visual sexual stimulation have a higher FMD (43.8+/-38%) than those who did not (18.52+/-14.37%, P=0.008). We confirm clinically that PEF is strongly impaired in organic ED linked to neurological, vascular and endocrine factors.