The efficacy of silymarin treatment in preventing biochemical and histological alterations in CCL4-induced liver cirrhosis in rats was studied. Four groups of rats were treated with: (1) CCL4; (2) mineral oil; (3) CCL4 + silymarin; and (4) silymarin. All animals were sacrificed 72 h after the end of treatments. The activities of alkaline phosphatase (alk. phosp.), gamma-glutamyl transpeptidase (GGTP), glutamic pyruvic transaminase (GPT) and glucose-6-phosphatase (G6Pase), and bilirubin content were determined in serum. Na+, K+-ATPase and Ca++-ATPase activities were measured in isolated plasma membranes. Lipoperoxidation, triglycerides (TG), and glycogen contents were also measured in liver homogenates. Liver cirrhosis was evidenced by significant increases in liver collagen, lipoperoxidation, serum activities of alk. phosp., GGTP, GPT, G6Pase, bilirubin content, and liver TG. Activities of ATPases determined in plasma membranes were significantly reduced, as was liver glycogen content. Silymarin cotreatment (50 mg/kg b.wt) completely prevented all the changes observed in CCL4-cirrhotic rats, except for liver collagen content which was reduced only 30% as compared to CCL4-cirrhotic rats. Silymarin protection can be attributed to the agent's antioxidant and membrane-stabilizing actions.