The purposes of this study were to clarify the role of neutrophilic proteases in the pathogenesis of hepatic ischemia/reperfusion injury and to determine whether urinary trypsin inhibitor (UTI) pretreatment attenuated liver ischemia/reperfusion injury in rats. Livers from male Sprague-Dawley rats were subjected to 90 min of no-flow warm ischemia followed by 120 min of reper-fusion. Rats were divided into a UTI group and a control group. In the control group, 120-min reperfusion of the liver produced a significant increase in myeloperoxidase activity, a significant decrease in ATP and energy charge, and a marked increase in the serum aspartate aminotransferase, alanine aminotransferase, and lactic dehydrogenase levels. In the UTI group, the myeloper-oxidase activity was significantly attenuated (i><0.01), ATP and energy charge were significantly improved (P<0.01 and P<0.05, respectively), and the elevation in serum aspartate aminotransferase, alanine aminotransferase, and lactic dehydrogenase was also markedly suppressed (P<0.05, P<0.01, and P<0.05, respectively) compared with the control group. Sections through the livers of control rats showed severe hepatocyte necrosis with neutrophil infiltration. In the UTI group, there was slight congestion and hepatocyte necrosis. The survival rate after 90-min liver ischemia was significantly improved compared with that in the control group (P<0.05). The results of this study suggest that pretreatment with UTI significantly attenuates liver reperfusion injury, perhaps by inhibiting neutrophil proteases.