An experimental study was conducted in the rat to evaluate the sensitivity of the liver to hyperthermia and ischemia. A 15-min asanguineous isolated hyperthermic in vivo perfusion of the liver was done in rats with a normal liver and in rats with an hepatocarcinoma induced by chronic 3'-diethylaminoazobenzene intoxication. The perfusion was made using various ranges of temperature of the perfusate. In normal rats, the in vivo perfusion was well tolerated as long as the mean intrahepatic temperature remained under 38 degrees C. Postoperative evolution of serum transaminase level was similar whatever the temperature of the perfusate. Histological lesions of the hepatic parenchyma were as severe as the temperature of the perfusate was elevated. In rats with tumors, the mortality rate was elevated in the animals with large tumors. A moderate decrease in the serum alpha-fetoprotein level was observed during the first days after liver perfusion. In all cases, death occurred apparently as a direct consequence of liver injury. This study defines the sensitivity of the normal or neoplastic rat liver to hyperthermia and ischemia using a model of isolated in vivo perfusion of the liver. It provides a basis for further investigations on the effect of hyperthermia on experimental liver tumors.