We attempted to clarify the role of color Doppler sonography in assessing the vascular function of untreated Peyronie's disease. A total of 50 patients with a mean 20-month history of penile curvature underwent color Doppler sonography with the penis in the flaccid state and after intracavernous injection of 20 micrograms. prostaglandin E1. Of the patients 41 (82%) complained of various degrees of erectile dysfunction, while 9 (18%) reported sustained rigid erections. Pathological peak systolic flow velocities (less than 30 cm. per second) of the cavernous arteries were found bilaterally in 10 patients (20%) and unilaterally in 10 (20%). Peak systolic flow velocity correlated positively with cavernous artery flow volume and with acceleration. Cavernous artery end diastolic velocity and resistance index, measured 15 and 30 minutes after vasoactive injection and genital manipulation, were indicative of corporeal veno-occlusive dysfunction (greater than 10 and less than 0.75 cm. per second, respectively) in 32 patients (65%). Of these patients, 11 (22%) had mixed arteriovenous dysfunction and 9 (18%) had normal cavernous artery flow velocities. Flow along the cavernous arteries is sometimes altered in cases of Peyronie's disease while corporeal veno-occlusive dysfunction seems to be the main hemodynamic abnormality. Color Doppler sonography should be considered as the initial step in the diagnostic evaluation of patients with Peyronie's disease who may be eligible for surgical treatment.