||Sheng Mai San (SMS) is a compound formulation in traditional Chinese medicine, consisting of Radix Ginsenq, Fructus Schisandrae and Radix Oohiooosonis. In the present study, the in vivo antioxidant properties of SMS were investigated using a rat model of carbon tetrachloride (CCl4)-induced hepatotoxicity. The antioxidant profile of SMS was also examined in several in vitro systems. Twenty-four hours after dosing rats with CCl4 at 1 ml/kg, an impairment in hepatic antioxidant status, as evidenced by increases in sensitivity of liver homogenates to glutathione (GSH) oxidation (induced by tert-butylhydroperoxide) and thiobarbituric acid reactive substances (TBARS) formation (induced by ferric chloride) and decrease in hepatic GSH content, was associated with elevations in hepatic malondialdehyde level and plasma alanine aminotransferase activities, indicating oxidative hepatocellular damage. Hepatic glutathione reductase and Cu,Zn-superoxide dismutase activities were also decreased. SMS-crude extract pretreatment caused significant protection against CCl4-induced hepatocellular damage, with a parallel enhancement in hepatic antioxidant status. SMS-aqueous fraction pretreatment significantly enhanced the hepatic GSH status and protected against hepatocellular damage in CCl4-treated rats. Although SMS-butanol fraction pretreatment inhibited ferric chloride-induced TBARS formation, it did not produce any effect on hepatic GSH status nor protect against hepatocellular damage induced by CCl4. SMS chloroform fraction, while increasing the sensitivity of liver homogenates to ferric chloride-induced TBARS formation, caused significant increase in hepatic glucose-6 phosphate dehydrogenase (G-6-PDH) activities and protection against CCl4-induced hepatotoxicity. A positive correlation between hepatic GSH status and hepatoprotection against CCl4 toxicity was apparent. Using in vitro systems measuring ferric chloride-induced peroxidation of erythrocyte membrane lipids and oxidation of ascorbic acid, SMS fractions were found to possess iron chelating activities. In addition, SMS fractions could scavenge hydroxyl and superoxide radicals as well as ferriheme oxidants. SMS fractions also inhibited GSH oxidation and enhanced GSH regeneration in liver homogenates. Although SMS butanol fraction had the highest in vitro antioxidant activities (except for the GSH regeneration), no apparent hepatoprotection was detectable in our in vivo rat model of CCl4 hepatotoxicity. The ensemble of results supports our hypothesis that the hepatoprotection afforded by SMS pretreatment is caused by its action in enhancing hepatic GSH status, possibly through G-6-PDH-mediated processes.