PBI was measured in 555 patients chosen at random from those who visited our impotence clinic between October 1984 and September 1986. Of 555 patients with impotence 29 (5.2%) showed a low PBI level of less than 0.6. On the basis of carefully taken history, risk factors causing the disturbance of penile blood flow were found in 13 (44.8%) of these 29 patients. They included diabetes mellitus, hypertension, surgery of pelvic organ, vertebral injury, vascular disorder of brain and gangliosympathectomy. Although penile angiography is necessary to make the definite diagnosis of vasculogenic impotence, hospitalization is usually required to perform the examination. Measurement of PBI is useful as a screening test to detect vasculogenic impotence at an outpatient clinic, because this examination is noninvasive and technically easy.