To establish the most suitable temperature for liver preservation, we preserved rat livers at various temperatures (0, 5, 10, and 15 degrees C) in UW solution and investigated, biochemically, the proton ATPase activity, ATP metabolites in mitochondria, and phosphatidyl-choline hydroperoxide (PC-OOH) in liver tissue. Liver specimens were taken every 6 h up to 24 h. The proton ATPase activity and the concentration of ATP, ADP, AMP, and adenosine in livers preserved at 0 degree C showed the best results. The total adenine nucleotide (TAN) in livers preserved for 18 and 24 h had significantly higher concentrations compared with those at other temperatures (5, 10, and 15 degrees C). In the livers preserved at 5 degrees C, TAN was degraded to hypoxanthine. On the other hand, those preserved at both 10 and 15 degrees C showed changes from hypoxanthine to xanthine. The concentration of xanthine in both groups preserved at 10 and 15 degrees C showed high values at 6 and 12 h, respectively, and similar changes in PC-OOH concentrations at both 10 and 15 degrees C were observed. However, the changes in PC-OOH concentration at various temperatures were not significant for any length of preservation time. In light microscopical examinations, there were no morphological changes in the hepatocytes. From these results, we conclude that the capability of ATP synthesis of mitochondria in livers preserved at 0 degree C keep them in the best condition compared with livers preserved at 15, 10, and 5 degrees C.