A prospective blinded comparison of duplex Doppler ultrasound (DDU) and a magnetic resonance angiography (MRA) 2-D time-of-flight technique was performed to assess the hepatic vasculature in 23 adult patients referred for orthotopic liver transplantation. Both techniques confirmed patency of the inferior vena cava in all patients, demonstrated a complete portal vein occlusion in one patient, and accurately defined the vascular and organ anatomy in a patient with situs inversus. The results were confirmed at surgery in 18 of the patients who have subsequently undergone liver transplantation. In one patient a partial portal vein thrombosis was found at surgery which was not detected by either imaging technique. MRA was more sensitive overall in detecting porto-systemic collaterals (31 locations in 17 patients) compared with ultrasound (24 locations in 17 patients), although ultrasound detected more patients with recanalized para-umbilical veins (DDU: 10 patients; MRA: 8 patients). These results indicate that a simple MRA technique can equal duplex Doppler ultrasound for the non-invasive assessment of patency of the hepatic vasculature and should be considered when DDU examination is equivocal or technically inadequate. MRA may provide additional information on the presence and size of porto-systemic collaterals which may be of value in monitoring portal hypertension.