Systemic and hepatic circulatory changes were studied in rats over the course of acute liver injury. Hepatic injury was induced by intraperitoneal injection of D-galactosamine (1.1 g/kg), and systemic and hepatic hemodynamics were measured over a 72-h period using a radioactive microsphere technique with direct measurement of arterial, portal venous, and hepatic venous blood oxygen content. Cardiac output increased to a maximum at 48 h, producing a marked increase (450%) in hepatic arterial blood flow so that it became the dominant supply of oxygen at the time of maximal hepatic injury. A subsequent increase in portal venous flow resulted in an overall increase in total hepatic blood flow of 500%. At this point the oxygen delivery by the hepatic arterial and portal venous systems was equal. These circulatory changes returned to control values by 72 h with recovery of liver function. These results demonstrate the development of a hyperdynamic circulation and a marked change in the normal relationship between portal venous and hepatic arterial blood flows that occur during hepatic injury.