To explain the cytotoxicity of excessive free radical production in the liver of rats, the lipoperoxidation in subcellular structures and some antioxidants systems were evaluated. We measured Cu-Zn superoxide dismutase (Cu-Zn-SOD) activity, reduced glutathione (GSH) levels and lipid peroxidation in homogenates and subcellular fractions of hepatocytes. Female Wistar rats were given a 0,2 per cent solution of CUSO4 in water, to induce the Cu toxicity. Serum copper levels and acid phosphatase (AP) activity were determined at frequent intervals. Six treated rats were euthanased to the twelfth week of begun the assay. During the sixteenth week, at time of the increase of serum AP activity the others treated rats also were killed. We found high liver Cu content and evidence of lipid peroxidation. In whole homogenate, mitochondrial and microsomal fractions, the thiobarbituric acid reacting substances were increased. This was correlated with an increase in the Cu-Zn-SOD activity and with decrease of the GSH levels. It could be argued that high copper status might have increased the Cu-Zn-SOD activity and induced lowest levels of GSH. Additionally, lipid peroxidation was induced by Cu-overload.