The aim of this study was to investigate the effect of betaine or taurine on liver fibrogenesis and lipid peroxidation in rats. Fibrosis was induced by treatment of rats with drinking water containing 5% ethanol and CCl(4) (2 x weekly, 0.2 ml/kg, i.p.) for 4 weeks. Ethanol plus CCl(4) treatment caused increased lipid peroxidation and disturbed antioxidant system in the liver. Histopathological findings suggested that the development of liver fibrosis was prevented in rats treated with betaine or taurine (1% v/v in drinking water) together with ethanol plus CCl(4) for 4 weeks. When hepatic taurine content was depleted with beta-alanine (3% v/v in drinking water), portal-central fibrosis induced by ethanol + CCl(4) treatment was observed to proceed cirrhotic structure. Betaine or taurine was also found to decrease serum transaminase activities and hepatic lipid peroxidation without any change in hepatic antioxidant system in rats with hepatic fibrosis. In conclusion, the administration of betaine or taurine prevented the development of liver fibrosis probably associated with decreased oxidative stress.