OBJECTIVE:To study the effects of Tibetan medicine Zuotai on the activities of cytochrome oxidase (CYP1A2) and drug metabolism enzyme N-acetyltransferase 2(NAT2)in rats. METHODS:70 SD rats were equally randomized into a normal control (normal saline) group,the groups of single administration of low,middle and high-dose (1.2,3.8 and 12 mg/kg) Zuotai and the groups of multiple administrations thereof(once daily for 12 consecutive days). The rats were given drugs ig. caffeine(25 mg/kg)was given ig to the rats in the normal control group and the groups of single administration on the 2nd day,and to those in the groups of multiple administrations on the 13th day. 5 h later,their urine was collected and added with vitamin C based on 10 mg/ml. High performance liquid chromatography (HPLC) was adopted to determine the cafeine metabolites contents of 5-acetami-do-6-formamido-3-methyl-uric acid(AFMU),1-methylxanthine(1X),1-methyl-uric acid(1U)and 1,7-dimethyl uric acid(17U) in rats’urine,and the activities of CYP1A2 and NAT2 were reflected through (AFMU+1X+1U)/17U and AFMU/(AFMU+1X+1U). RESULTS:Compared with normal control group,the(AFMU+1X+1U)/17U and AFMU/(AFMU+1X+1U)in rats were de-creased,namely the activities of CYP1A2 and NAT2 were lower in the groups of single administration of middle-dose Zuotai and multiple administrations of middle and high-dose Zuotai than in the normal control group. There was statistical difference (P<0.05). CONCLUSIONS:Zuotai can obviously inhibit the activities of CYP1A2 and NAT2 in rats.