We tested the possibility of using intracavernous injections of the alpha-blocking agent moxisylyte (6-acetoxy-thymoxy-ethyl-dimethylamine) as treatment of erectile impotence. Laboratory studies proved moxisylyte to be more active than saline (double-blind with crossover) but less active than papaverine (crossover), since it induced prolonged erection in most patients but rigid erection in only a few. However, penile vibration proved to enhance the moxisylyte effects, the combination resulting in rigid erection in 5 of 8 patients tested. Repeated office injections of moxisylyte in 70 patients resulted in clear improvement of impotence during the subsequent weeks in 50 per cent of the psychogenic, and 18 per cent of the organic and mixed impotent patients. Of 91 impotent patients 42 achieved satisfactory intercourse within 2 hours after an office injection, although previously the same dose induced a rigid erection in the office in only 24. Of 37 patients instructed in moxisylyte self-injections 92 per cent achieved successful results without any significant side effect. The main advantage of moxisylyte proved to be its safety, allowing for less compelling precautions than with papaverine: only 2 of the 170 patients injected with moxisylyte at our clinic had prolonged erections, that is 1.1 per cent compared to 14 per cent in a personal series who received papaverine. In regard to the therapeutic applications of intracavernous injection facilitating drugs, such as moxisylyte, should be tried first, with use of the more potent but also more dangerous drugs, such as papaverine, only when impotence fails to improve.