A multidisciplinary study was performed on 200 consecutive patients with erectile dysfunction more than 1 year in duration, which included a standardized intracavernous injection of a vasoactive substance mixture (15 mg. per ml. papaverine plus 0.5 mg. per ml. phentolamine). The multidisciplinary findings correlated well with the intracavernous dose needed for full erection. The group without pathological hemodynamic findings (36 patients) needed an average of 0.67 ml. and the group with pathological inflow (107) needed an average of 1.07 ml. In the venous insufficiency group (57 patients) only 18 achieved full erections with an average of 2.1 ml. (39 achieved tumescence only to 3 ml.). The results show that standardized intracavernous injection of a vasoactive substance mixture is a useful method to evaluate penile hemodynamics. This pharmacological test appears to be effective in the differential diagnosis of nonvascular and vascular erectile dysfunction.