The compound herbal medicine Wu-chu-yu-tang is used for the treatment of migraine and vomiting accompanying a cold. To assess the interactions of herb and drug metabolism, effects of Wu-chu-yu-tang on hepatic and renal cytochrome P450 (CYP), UDP-glucuronosyl transferase (UGT) and glutathione S-transferase (GST) were studied in C57BL/6J mice. Treatment of mice with 5 g/kg per day Wu-chu-yu-tang for 3 days caused 2.5-fold and 2.9-fold increases of liver microsomal 7-ethoxyresorufin O-deethylation (EROD) and 7-methoxyresorufin O-demethylation activities, respectively. However, CYP activities toward 7-ethoxycoumarin, benzphetamine, N-nitrosodimethylamine, erythromycin and nifedipine, and conjugation activities of UGT and GST were not affected. In kidney, Wu-chu-yu-tang-treatment had no effects on Cyp, UGT and GST activities. Among the four component herbs of Wu-chu-yu-tang, only Evodiae Fructus (Wu-chu-yu) extract increased EROD activity and CYP1a2 protein level. In E. Fructus, rutaecarpine, evodiamine and dehydroevodiamine are the main active alkaloids. At the doses corresponding to their contents in Wu-chu-yu-tang, rutaecarpine-treatment increased hepatic EROD activity, whereas evodiamine and dehydroevodiamine had no effects. These results demonstrated that ingestion of Wu-chu-yu-tang elevated mouse hepatic Cyp1a2 activity and protein level. E. Fructus and rutaecarpine contributed at least in part to the CYP1a2 induction by Wu-chu-yu-tang. Patients should be cautioned about the drug interaction of Wu-chu-yu-tang and CYP1A2 substrates.