We present a review of ultrasonic Doppler methods (duplex scanning) used in the noninvasive assessment of renal artery stenosis and hemodynamics. The clinically successful applications of ultrasonic Doppler methods to the noninvasive assessment of the peripheral and cerebral vasculatures have prompted investigators to apply these methods to the renal artery. Various Doppler criteria for the diagnosis of renal artery stenosis have given sensitivities and specificities that range from 31% to 91% and 88% to 100%, respectively. Furthermore, estimates of renal vascular flows and resistances can be made in echogenic subjects. The technical success rate of the method is operator dependent, consequently, reliable duplex scanning of the renal arteries may be limited to experienced ultrasound laboratories.