Duplex ultrasound studies and color Doppler imaging have substantially enhanced the diagnostic capabilities of abdominal ultrasonography. The status of the flow in the major abdominal vessels is routinely obtainable along with anatomic information about the organs that they supply. The current applications of duplex and color Doppler imaging in evaluating the hepatic vascular system, hepatic transplants, aorta, splanchnic arterial system, renal artery and vein, renal transplants, and penile arterial system are reviewed. The indications for and limitations of these examinations, as well as the potential future uses, are discussed.