The number of clinical liver transplants that can be performed is limited by the availability of suitable donor organs. If it were possible to harvest and use livers after cardiac arrest, the supply could be improved. The mechanisms of damage in warm ischemia are not yet well understood and the consequences of transplanting a liver that is unable to provide immediate life-support are unacceptable. This study aims to identify areas for more detailed study in an attempt to improve the quality of livers harvested after significant warm ischemia, and to select acceptable organs for transplantation. Porcine livers were subjected to 75 min of warm ischemia and then perfused at 37 degrees C for 3 hr, during which period biochemical monitoring was carried out. At the end of the perfusion, histological and transmission electron microscopical studies were made. Large amounts of the intracellular enzymes ALT, AST, and LDH were released into the perfusate during the first 30 min of perfusion, but this--and the further amounts released during the subsequent 2.5 hr--was influenced by the composition of the perfusate. The inclusion of the substrates fructose and oleate, plus amino acids, substantially reduced this release and also improved the ability of the livers to metabolize ammonia. Oxygen free-radical scavengers had a significant, but smaller, beneficial effect. Electron microscopy confirmed the value of perfusion in improving cell morphology, and the additional value of including metabolic substrates. This study shows that hepatocellular structure and function can be improved by appropriate perfusion methods that also provide a simple means of monitoring some important functions. Both metabolic support and neutralization of oxygen free-radical action have a role to play in this approach to rendering ischemically injured livers acceptable for clinical use.