The usefulness of a chemical prosthesis was studied for the diagnosis and treatment of 20 patients with erectile impotence (14 due to diabetes, 2 due to pelvic surgery and 4 due to psychogenic factors) using papaverine hydrochloride and phentolamine mesilate. Absolute erection was observed in 16 patients (80%) and coital penetration was possible in all 9 patients who actually tried sexual intercourse. Penile arterial blood flow was measured in 15 patients using a real-time mechanical sector duplex scanner (Diasonics DRF/400V) just before and after the chemical prosthesis, and a marked increase in blood flow was observed in all patients after administration. From these results, it is considered that measurement of the penile blood flow using a mechanical sector duplex scanner is useful in the diagnosis and monitoring of impotence. Furthermore, a chemical prosthesis is suitable mainly for the treatment of impotence due to diabetes, by adjusting the dosage and administration.