In isolated rat hepatocytes aromatic hydroxylation and oxidation of the 14C-phenazepame heterocycle were studied. Both these reactions proceeded with the linear rate in intact hepatocytes and aromatic hydroxylation predominated. After induction of cytochrome P-450 by phenobarbital the rate of the heterocycle oxidation was increased 3.6-fold. Rates of aromatic hydroxylation and the phenazepame heterocycle oxidation did not depend on administration of phenobarbital and 3-methyl cholanthrene into the animals. Effects of the factors studied (concentration of phenazepame, induction of cytochrome P-450 by means of phenobarbital and 3-methyl cholanthrene) on alterations in the rate of oxidation of both aromatic nuclei and the phenazepame heterocycle were estimated using dispersion analysis.