Doppler ultrasound was used to detect experimental and clinical renal artery stenosis (RAS) and increased renovascular resistance (RVR). Parameters assessing RAS included elevated systolic frequency and spectral broadening, while diastolic/systolic frequency ratios predicted elevated RVR. In canine models these parameters detected graded RAS before reduction in renal blood flow. Index values were 88% sensitive and 100% specific in identifying RAS with gradients greater than or equal to 25 mm Hg. Diastolic/systolic frequency correlated well with increased RVR induced by microsphere injections (p less than 0.05). Duplex scanning noninvasively detected bilateral renal artery velocity in 113 of 120 patients. Index values were 83% sensitive and 97% specific in identifying greater than or equal to 60% RAS in 86 vessels visualized by angiography. Estimated RVR was significantly higher in age-matched hypertensive and atherosclerotic patients than in controls (p less than 0.01). Ultrasound may be useful to screen patients for RAS and increased RVR.