The optimal preservation temperature for liver allografts is unknown. We evaluated the effect of small differences in preservation temperature, 5°C vs 0°C, on outcome of prolonged preservation. Livers of Wistar rats were preserved at these temperatures in UW solution for 40 h. Function was studied during reperfusion on the isolated perfused rat liver system at 37°C. To compare the effects of a small reduction in temperature with known beneficial strategies, the effects of including antiproteases and periodic flushing of the graft with UW solution during cold preservation at 5°C were also studied. Aspartate transaminase (AST) and alanine transaminase release after 4 h of reperfusion were much higher in the livers stored at 5 than at 0°C (P <; 0.0005). Addition of antiproteases to the preservation solution or periodic flushing reduced AST release but neither treatment at 5°C was as good as simple storage at 0°C. Cumulative bite production after 4 h of reperfusion was significantly greater in the 0°C preserved group than in liver at 5°C or 5°C with periodic flushing. The addition of antiproteases resulted in slightly increased bile production (not significant). Platelets and WBCs in the perfusate decreased during reperfusion. This effect was more pronounced in the 5°C preserved livers than in those stored at 0°C. Antiproteases in the preservation solution appeared to inhibit platelet and WBC loss. Perfusate flow was significantly higher in the 0° C group. We conclude that small differences in preservation temperature even at these low temperatures are important in postreperfusion liver function.