We determined whether the comparison between equilibrium pressure after intracavernous injection of vasodilators and maximal corporeal pressure at gravity cavernosometry could provide information about the relative contribution of arterial inflow and cavernous wall resistance to the erection process. The results of gravity cavernosometry performed in 68 impotent patients were compared to those of duplex scanning in 53 and penile angiography in 10. A highly statistically significant (p < 0.01) but nonlinear correlation was observed between the equilibrium pressure after injection and maximal corporeal pressure, which indicates a paramount role of the corporeal veno-occlusive mechanism in the development of penile rigidity. However, in most patients with a pressure increase of more than 30 mm. Hg from the equilibrium pressure after injection to the maximal corporeal pressure, arterial insufficiency was diagnosed by duplex scanning and/or arteriography, and seemed to be the main limiting factor in the development of penile rigidity. Gravity cavernosometry provides functional information about the corporeal veno-occlusive mechanism and arterial inflow and, therefore, about the relative roles of these mechanisms in the development of penile rigidity.