Reperfusion injury represents an accentuation of the hypoxic injury caused by the restoration of oxygenated blood flow to the liver after a period of anoxia or hypoxia. Reoxygenation injury may occur after any ischaemic episode, but the most dramatic form in clinical hepatology occurs during orthotopic liver transplantation and after unclamping of the portal vessels during liver resection. Reactive oxygen radicals appear to play an important role in the development of such injury, as has been demonstrated by direct measurements of their release and by the protective effects of antioxidants. The relative contribution of the various liver cell types to the release of reactive oxygen species and the differences in sensitivity to ischemic and reperfusion injury between liver cell subtypes are discussed. (Fig. 3, Ref. 31.)