Continuous vasopressin infusion has been shown to control bleeding from oesophageal varices in patients with cirrhosis of the liver. The mortality, however, has not been changed. To investigate whether reduction of portal blood flow over a period of hours deteriorates the liver function, we measured the splanchnic blood flow and galactose and oxygen consumption in five cirrhotic patients during liver vein catheterization. Vasopressin was given as a continuous infusion of 0.2 units per min for three h. The splanchnic blood flow was reduced to 70% of control values and remained so throughout the infusion. After three h no impairment of the liver function was found. The wedged hepatic pressure (portal pressure) rose slightly, probably due to the increase of the central venous pressure reflecting impaired cardiac function. The reported beneficial effect of vasopressin on varix bleeding probably depends on the reduced portal flow per se.