PURPOSE: To evaluate the usefulness of double injection of a vasoactive drug in penile Doppler ultrasonography for the diagnosis of vasculogenic impotence. MATERIALS AND METHODS: Eighty-four consecutive cases (bilateral sides) of 42 patients with suspected vasculogenic impotence were included in our study. We used computed sonography (Acuson, USA), with a 7 MHz linear array transducer. After the first intracavernosal injection of the vasoactive drug (10 ug of prostagladin E1), peak systolic velocity (PSV) and end diastolic velocity (EDV) were measured three times. According to mean PSV and EDV, the patients were classified into four groups : arteriogenic impotence (AI;N=29), venogenic impotence (VI;N=28), AI associated with VI(N=14), and normal(N=13).After the second injection, PSV and EDV were remeasured, using the same method. Mean velocities of the first injection were compared with those of the second, and the paired t-test was used to analyze the results. the extent to which patients were reclassified after the scecond injection we noted. RESULTS: In all four groups, PSV measured after the second injection was significantly different from PSV after the first (p=0.0001, 0.0001, 0.0010, 0.0072); except in the normal group, EDV measured after the second injection was not different from EDV after the first (P=0.9815, 0.0654, 0.0950, 0.0057). After the second injection, the numbers of patients reclassified into other groups were as follows : AI, 11 (38%); VI, 6 (21%); AI associated with VI, 11 (79%); normal, 1 (8%). CONCLUSION: Double injection of a vasoactive drug affected PSV, and therefore, appears to be a useful adjunctive procedure for the evaluation of patients in whom classification based on the results of the first injection is difficult.