Lipid peroxidation increased both in the liver homogenates and in the hepatic mitochondrial fraction of bile duct ligated (BDL)-rats. Although mitochondrial superoxide dismutase (SOD) activity did not change in the liver, glutathione (GSH) levels and glutathione peroxidase (GSH-Px) activity decreased in hepatic mitochondrial fraction of BDL-rats as compared to sham-operated rats. In addition, GSH-Px and glutathione transferase (GST) activities decreased but SOD activity remained unchanged in the post-mitochondrial fraction of the liver from BDL-rats. However, erythrocyte lipid peroxide and GSH levels did not change in BDL-rats. In conclusion, our results show that the disturbance of oxidant-antioxidant balance especially in mitochondria may be responsible for cholestatic injury in BDL-rats. (C) 1997 The Italian Pharmacological Society.