A total of 100 men with organic impotence underwent a trial of intracavernous drug-induced erections with a mixture of papaverine (25 mg./ml.) and phentolamine (0.8 mg./ml.). The response rates, that is functional erections, were 100 per cent in patients with neurogenic impotence, 65.7 per cent in those with vasculogenic impotence, 90 per cent in the undetermined group and 64.7 per cent in the neurogenic/vascular impotence group. Of the responders 79.5 per cent elected to practice self-injection as a method to restore erectile function. The dose required to obtain functional erections in the purely neurogenic impotence group was significantly lower than that required in other groups. Complications were few and included 4 patients with sustained erections that required intervention. Intracavernous injection of vasoactive drugs appears to have promising value in the treatment and differential diagnosis of erectile dysfunction.