A Doppler ultrasound probe was used in 42 men to evaluate penile circulation. Twenty-six patients had confirmation of vascular anatomy by pelvic arteriography. The average penile acceleration (peak velocity over pulse rise time) relative to the radial artery acceleration was expressed as the penile flow index. Eleven potent men had a penile flow index of 3.4 plus or minus 0.4 standard error, while 13 impotent men with vascular disease on arteriography had a penile flow index of 21.7 plus or minus 5 standard error (p less than 0.01). Patients with intermediate penile flow index values had variable degrees of erectile failure. This relatively simple, non-invasive technique identifies a vascular component of impotence, thus aiding in the selection of appropriate management.