Age-associated changes in liver injury and post-necrotic regeneration were studied in rats aged 6 and 30 months in a period of 96 h following a dose of thioacetamide (6.6 mmol/kg body weight). Hepatocellular necrosis was detected in both groups by serum aspartate aminotransferase, but the severity of injury was significantly lower (one fourth, p < 0.001) in the oldest. Differences were observed in hepatocyte FAD monooxygenase activity between 6 and 30 months old rats at 24 h (278 versus 170%, p < 0.001, respectively) and also in GSH/GSSG ratio, in protein thiol groups and in malondialdehyde. Glutathione peroxidase, glutathione reductase and glucose-6-phosphate dehydrogenase activities rose markedly in both groups, this increase being slightly lower in the oldest. Superoxide dismutase and catalase did not show significant changes between both groups. At the end of the 96 h experimental period the restoration towards normal of GSG/GSSG, protein thiols malondialdehyde and the activities of Cu-Zn superoxide dismutase and catalase were significantly lower in hepatocytes from 30 months old rats. We summarize that the main age-related changes in the sequenced process of liver injury and regeneration occurred to a lesser extent in severity of injury and delayed response in the post-necrotic restoration of liver function, probably due to a lower increase in antioxidant enzyme system.