In diagnostic screening, 73 impotent patients were submitted to a Doppler study of the deep penile arteries under basal conditions and after oral nitroglycerin (Basal-DOPPLER) and after intracavernosal injection of 30 mg of papaverine (ICIP-DOPPLER), as well as other tests. The results of the Basal-DOPPLER and the erectile response to intracavernosal administration of 30 mg papaverine (ICIP-30), indicative of the condition of the deep penile arteries, were in total agreement for 33 cases, partial agreement for 29 cases and totally in disagreement for 11 cases. The agreement between the results of the ICIP-DOPPLER and the ICIP-30 was total for 40 cases, partial for 24 and totally lacking for 9. In many of the cases for whom the response to ICIP-30 was less than would have been expected from the ICIP-DOPPLER, abnormal venous outflow was later shown. Our data support the hypothesis that papaverine acts on the venous component of erection. The ICIP-DOPPLER was found to be apparently more reliable than the Basal-DOPPLER for evaluating the arterial component of erection, but Basal-DOPPLER is still the basic screening test before any such invasive test as the ICIP are used, since these latter are not always accepted immediately by the patients.