Biochemical markers of ischemic injury of rat liver were studied in an extracorporeal perfusion system. During anoxic perfusion, purine compounds appeared in the perfusate as soon as they were formed in the liver and their recovery in the perfusate balanced the loss of adenine nucleotides from the liver. In contrast, cytosolic aspartate aminotransferase did not appear in the perfusate at slow rates of liver perfusion or during hypothermic perfusion. The production of purine compounds was further investigated in hypothermically preserved liver in connection with the restoration of some metabolic functions of liver. The amount of purine compounds released into the perfusate was found to be closely related to the degrees of damage of the hepatic functions of gluconeogenesis, ureogenesis, and mitochondrial respiration on reperfusion. These results indicate that release of purine compounds into the perfusate is a good marker of ischemic damage.