In order to study the effects of Rhei rhizoma, Ephedrae herba and Scutellariae radix on hepatic metabolism, we examined the pretreatment effect of those on the metabolism of 7-e thoxycoumarin (EC). Water extracts (1g/kg) of Rhei rhizoma, Ephedrae herba and Scutellariae radix were administered orally to rats for 7 days, respectively. Livers were then isolated and perfused with 100mcM EC for 2 hours. The metabolites of EC, 7-hydroxycoumarin, sulfate conjugate and glucuronide conjugate were measured in the perfusates. The amount of glucuronide conjugates was decreased in Rhei rhizoma pretreated rats (p<0.01), however, 7-hydroxycoumarin was increased in Ephedrae herba pretreated rats (p<0.01). We examined whether the change of enzyme activity is related to the change of cytochrome P4501A1 and P4502B1 mRNA level in the perfused rat liver, which are responsible for EC metabolism. CYP1A1 and CYP2B1 mRNA level was increased, which was was not statistically significant with rhei rhizoma nor ephedrae herba pretreatment. We also assessed the hepatotoxicity of Rhei rhizoma, Ephedrae herba and Scutellariae radix. The activities of ALT and AST were assayed at 24 hours after 7 days administration. Only the ratio of ALT over AST was increased in ephedrae herba pretreated rats (p<0.05). Lipid peroxidation was increased in Rhei rhizoma treatment (p<0.05), while histopathological examination performed after liver perfusion did not show any difference compared with vehicle treatment. These results suggest that Ephedrae herba pretreatment increases the o-deethy-lation of 7-ethoxycoumarin in rats, which may be mediated by CYP1A1 mRNA induction.