The efficacy of papaverine, and a combination of papaverine and phentolamine as a pharmacological treatment of impotence was compared in a double-blind, crossover trial. A total of 40 impotent men received intracavernous injections of papaverine (40 mg.) or a combination of papaverine (20 mg.) and phentolamine (0.5 mg.) at monthly intervals. Observations at 20 minutes after injection demonstrated that papaverine caused full erections in 27 per cent of the men and partial erections in 65 per cent. The combined injection resulted in full erections in 48 per cent of the men and 52 per cent had partial erections. The difference was significant (Z equals 2.29, p less than 0.05).