Of 447 presenting with erectile dysfunction, 322 (72%) responded to intracavernous injection of PGE1 with erections that were adequate for sexual intercourse. A multidisciplinary comparative study of PGE1 and other vasoactive drugs, e.g., papaverine or the combination of papaverine and phentolamine, was performed in 249 patients. Whereas 180 of the 249 patients (72.3%) showed adequate erections after 10 or 20 micrograms PGE1, only 79 of them (31.3%) did so after papaverine. A further 72 of the 249 patients (29%) had adequate erections after papaverine/phentolamine; thus, a total of 151 of 249 patients (60.3%) developed good erections after papaverine/phentolamine. Whereas after PGE1 no patients at all suffered from priapism lasting more than 6 h, this occurred in 13 of 249 patients (5.2%) after papaverine or papaverine/phentolamine. After intracavernous injection of PGE1, 9.4% of the patients complained of uncomfortable penile sensations during erection interfering with sexual intercourse. Since the initial study, 60 patients have been instructed in self-injection therapy and a further 45 patients obtain intracavernous PGE1 injections periodically, with very promising results. In vitro studies of cavernosal tissue samples obtained from potent men with penile deviations showed both the excellent relaxation of the smooth muscles of cavernous bodies by PGE1 and the antiadrenergic effect of the drug.