From March to July 1989, a total of 40 patients, who had received coronary catheterization, answered questionnaires concerning sexual potency. In those 30 patients with a diseased coronary artery, only 2 (6.6%) had no erectile dysfunction subjectively. On the contrary, 4 of 10 (40%) patients with angiographically proven normal coronary artery complained of erectile dysfunction. Penile Doppler ultrasonography was performed in 30 patients. The mean penile brachial index (PBI) of 8 patients with a normal coronary artery was 0.82 +/- 0.1, as compared with the diseased group, 0.73 +/- 0.1 (p = 0.05). When these patients were further divided into two groups by a PBI of greater or less than 0.65, there was also no significant difference in the degree of obstruction of the three main coronary arteries between these two groups. There was no correlation between PBI and obstruction of the left anterior descending artery (r = 0.316, p = 0.689). Most of the patients (93.4%) with an abnormal coronary artery had erectile dysfunction. Nevertheless a poor correlation was noted between the PBI and the severity of coronary artery obstruction. Our study suggests that it is hard to use PBI alone as a predictor of future major thromboembolic heart attack.