Intracavernous injection of 20 micrograms prostaglandin E1-CD (PGE1-CD, 8 cases), 5 micrograms lipo prostaglandin E1 (Lipo PG-E1, 8 cases) or 10 micrograms Lipo PGE1 (9 cases) was performed in patients with functional impotence in order to comparatively analyze the diagnostic efficacy of these drugs. Full erection was observed in all patients who received intracavernous injection of 20 micrograms PGE1-CD or 10 micrograms Lipo PGE1. However, full erection was observed in 4 out of 8 patients administered 5 micrograms Lipo PGE1. RigiScan was used on all patients, and latency until erection (achievement of maximum rigidity of the base) after injection, maximum rigidity of the penile tip and base and circumferential expansion rate of the penile tip and base were measured. With regard to these RigiScan data and duration of erection, there were no significant differences among the 3 groups. There were no severe side effects in any of the patients. These findings indicate that 10 micrograms Lipo PGE1 and 20 micrograms PGE1-CD have similar effects and that Lipo PGE1 may be an effective drug for the diagnosis and treatment of impotence.