Cytochrome P-450 (P-450) isozymes of flavone-pretreated rats were compared with those of partially purified microsomal proteins and liver microsomes from control rats and phenobarbital (PB)-, 3-methylcholanthrene(MC)-, and isosafrole(ISF)-pretreated rats. The activities of microsomal P-450 dependent aryl hydrocarbon hydroxylase(AHH) and ethoxycoumarin deethylase(ECDE) were more than three times of those of control. AHH and ECDE activities of partially purified P-450 with DE_(52) column chromatography were increased more than eight times of control. Monoclonal MC 1-7-1 antibody, which is specific to P-450 c and d isozyme, bound specifically to liver microsomal P-450 of flavone-rats in radioimmunoassay. Some properties of P-450 of flavone-rats were identical with those of P-450 d in spectral and electrophoretic studies. The absorption maximum of P-450-CO complex of flavone-rats was 448 nm (same as that of MC-pretreated rats), and molecular weight of partially purified P-450 from the major band of electrophoresis was 52,000 (same as that of PB-pretreated rats). Thus, it can be indicated that the pretreatment of flavone induces P-450 d or P-450 isozyme with similar immunochemical properties to P-450 d.