A model for the in-vivo perfusion of the isolated rat liver with either cytotoxic agents or hyperthermic saline, administered through either the hepatic artery or the portal vein, is described. Rats were able to survive following perfusion with a dose of up to 0.25 g/kg of 5-fluorouracil and 2.0 to 2.5 mg/kg of mitomycin-C by both routes. Regional hyperthermic perfusion of the liver produced temperature and time-dependent hepatotoxic effects. A marked elevation of serum glutamic oxaloacetic and glutamic pyruvic transaminase levels was noted 24 hours after perfusion, but was reversible. Aminopyrine N-demethylase activity in both normal intact and regenerating rat liver was not affected; however, the activity in normal intact liver was markedly suppressed with hyperthermic perfusion at 43 degrees C only. Incorporation of tritiated thymidine into hepatic deoxyribonucleic acid 24 hours after partial hepatectomy was severely inhibited by prior hepatic perfusion with either cytotoxic drugs or hyperthermic saline. This in-vivo isolated perfusion technique could be used to assess the effect of thermochemotherapy on tumour growth in the liver.