AIM: To clarify the protective effect of exogenous adenosine triphosphate (ATP) on hypothermically preserved rat livers.METHODS: Establishment of continuous hypothermicmachine perfusion model, detection of nucleotides inhepatocytes with HPLC, measurement of activities of LDHand AST in the perfusate, observation of histopathologicalchanges in different experiment groups, and autoradiographywere carried out to reveal the underlying mechanism of theprotective effect of ATP.RESULTS: The intracellular levels of ATP and EC decreasedrapidly after hypothermic preservation in control group, whilea higher ATP and EC level, and a slower decreasing ratewere observed when ATP-MgCl2 was added to the perfusate(P＜0.01). As compared with the control group, the activitiesof LDH and AST in the ATP-MgCl2 group were lower (P＜0.05).Furthermore, more severe hepatocyte damage and neutrophil infiltration were observed in the control group. Radioactive [α-32P] ATP entered the hypothermically preserved rat hepatocytes.CONCLUSION: Exogenous ATP has a protective effect on rat livers during hypothermical preservation. However, Mg2+ is indispensable, addition of ATP alone produces no protective effect. The underlying mechanism may be that exogenous ATP enters the hypothermically preserved rat liver cells.