The present study was carried out to elucidate the relationship between the generation of reactive oxygen species (ROS) and an activation of nuclear factor (NF) kappa B in a hepatic ischemia-reperfusion model. During the ischemic period, the contents of xanthine oxidase (XOD) metabolites and thiobarbituric acid-reactive substances were significantly increased, and NF-kappa B was activated in the liver of rats. The activation of NF-kappa B was inhibited by pretreatment of allopurinol (10-100 mg/kg, i.p.) in a dose-dependent manner. In conclusion, this suggests that the XOD-derived ROS may activate NF-kappa B during ischemia.