Patients with cirrhosis and ascites often develop a particular form of renal failure known as hepatorenal syndrome (HRS), which is due to a vasoconstriction of the renal circulation (1). The histologic appearance of the kidneys in HRS is normal, and the kidneys regain a normal or near-normal function after liver transplantation. Both findings demonstrate the functional nature of HRS. Besides changes in renal function, patients with HRS also show marked abnormalities in the systemic arterial circulation and activity of endogenous vasoactive systems, which probably play a major role in the development of renal hypoperfusion.