Mitochondria, isolated from rat livers during the early phase of liver regeneration (7-24 h after partial hepatectomy), show: (i) decrease in the rate of ATP synthesis; (ii) increase of malondialdehyde and of oxidized protein production; (iii) decrease of the content of intramitochondrial glutathione and of protein thiols on mitochondrial proteins; (iv) increase of the glutathione bound to mitochondrial proteins by disulfide bonds. These observations suggest an increase of production of oxygen radicals in liver mitochondria, following partial hepatectomy, which can alter the function of the enzymes involved in the oxidative phosphorylation. Blue-native gel electrophoresis of rat liver mitochondria, isolated after partial hepatectomy, shows, during the early phase of liver regeneration (0-24 h after partial hepatectomy), a progressive decrease of the content of F0F1-ATP synthase complex. The amount of glutathione bound to the F0F1-ATP synthase, electroeluted from the blue-native gels, progressively increased during the early phase of liver regeneration. It is concluded that partial hepatectomy causes mitochondrial oxidative stress that, in turn, modifies proteins (such as F0F1-ATP synthase) involved in the mitochondrial oxidative phosphorylation.