A group of 25 patients underwent Doppler penile blood examination and cavernometry before and after 5 mg of phentolamine injected intracavernously. The organic or psychogenic nature of impotence was determined by psychological testing, the intracavernous injection of papaverine, hormonal evaluation, neurological examination, Doppler penile blood flow measurement and cavernometry for vascular investigations. The intracavernous injection of phentolamine had no effect on the venous return and it provoked penile arterial dilatation. The erectile angle, which was also measured, was less evident than after the injection of papaverine. The results confirmed the fact that an increase in arterial inflow alone is not sufficient to induce a rigid erection in man.