The purpose of this study is to evaluate the interaction effects of In-Chen-How(ArtemisiacapillariesThunb.) on the pharmacokinetics of acetaminophen and on liver microsomal cytochrome P450enzyme activity in rats.The rats were divided into control group(n=8) without In-Chen-How and thepretreated group(n=8) administered with In-Chen-How(approximately 1.0 mL.kg-1,according toweight) for5 consecutive days.Rats in the control group received water simultaneously.Each rat was thengiven acetaminophen.The pharmacokinetic parameters of acetaminophen of the two groups weresignificantly different.In the In-Chen-Howpretreated group,the maximumconcentration of acetaminophenand the area under the plasma concentration-time curve were reduced about58.4%,56.7% and 55.4%.To further explain the results,liver microsomal suspensions were obtained from rats that were randomlydivided into control and In-Chen-How pretreated group.The levels of CYP1A2 and CYP2E1 in hepaticmicrosomal protein from pretreated group were increased as compared to that from the control group.Itindicated that In-Chen-How can stimulate the activity of CYP isozymes.The changes in thepharmacokinetics of acetaminophen resulting from the administration of In-Chen-How are related to anincrease in metabolic activity of CYP1A2 and CYP2E1. The purpose of this study is to evaluate the interaction effects of In-Chen-How (Artemisiacapillaries Tubb.) On the pharmacokinetics of acetaminophen and on liver microsomal cytochrome P450 enzyme activity in rats. Rats were divided into control group (n = 8) without -Chen-How and the pretreated group (n = 8) administered with In-Chen-How (approximately 1.0 mL.kg-1, according toweight) for 5 consecutive days. Rats in the control group received water simultaneously. The pharmacokinetic parameters of acetaminophen of the two groups weresignificantly different. In In-Chen-Howpretreated group, the maximum concentration of acetaminophen and the area under the plasma concentration-time curve were reduced about 58.4%, 56.7% and 55.4% .To further explain the results, liver microsomal suspensions were obtained from rats that were randomly divided into control and In-Chen-How pretreated groups. The levels of CYP1A2 and CYP2E1 in hepaticmicrosomal protein from pretreated grou p were increased as compared to that from the control group. Indicated that In-Chen-How can stimulate the activity of CYP isozymes. the changes in the pharmacokinetics of acetaminophen resulting from the administration of In-Chen-How are related to an increase in metabolic activity of CYP1A2 and CYP2E1.