Intracavernous injection of various vasoactive drugs was performed in six erectile failure patients. The effects of each drug were evaluated in four grades: complete functional erection, incomplete functional erection, nonfunctional expansion and no effect. When papaverine hydrochloride (40 mg/ml) was administered, 4 of the 6 patients had nonfunctional expansion. By administering a mixture of 80 mg/ml papaverine hydrochloride with 1.0 mg/ml phentolamine mesylate, nonfunctional expansion was seen in four patients and incomplete functional erection in two patients. As for the effects of prostaglandin E1, incomplete functional erections were seen in all patients, while complete functional erection was seen in two patients. These findings indicated that the patients reacted differently to the same vasoactive drug, and that the papaverine and phentolamine mixture had a stronger effect than papaverine alone, while prostaglandin E1 had the strongest effect on erection. Intracavernous injection of the these drugs is useful for the treatment and differential diagnosis of impotence.