The effects of styrene on the induction of cytochrome P-450s (P450), (P4501A1/2, P4502B1/2 and P4502El) and activities of other related enzymes were investigated in the male Sprague Dawley rats which were treated with styrene 500 (S1), 1,000 (S2) 1,500 (S3) mg/kg in olive oil intraperitoneally once a day for two days and sacrificed for the preparation of liver microsomes after 24 hrs. 1. The contents of total protein and P450 in the microsomes derived from the styrene treated groups were slightly higher than those from the control group except those from the 53 group (1,500 mg styrene/kg body weight) . The decreases in microsomal protein contents was prominent in the S3 (p<0.05), but the P450 contents was increased significantly in the S2 (p<0.05). 2. The activities of NADPH-P450 and NADH b5 reductase in hepatic microsomes derived from the treated groups were significantly increased in the treated groups(p<0.05). 3. The activities of PROD were also prominently increased with the treatment of styrene except in 53 group, but the activity of EROD was decreased by styrene treatment. The activities of pNPH in the styrene treated groups were higher than that of the control group (p<0.05). 5. Western blotting with monoclonal antibodies against P4502B1/2 isozymes showed the presence of P4502B1/2 in hepatic microsomes from the rats treated with styrene, and the increase in the densities of immunoblots were corelated with the dosages of styrene. The blot densities against P4501A1/2 and P4502El were slightly increased in the styrene treated groups compared with the control group. These results suggested that styrene could primarily induce P4502B1/2 as major and P4501A1/2 and P4502El in minor forms for the metabolism of styrene in rats.