The ability of neonatal rat liver to form benzo[a]pyrene oxidative metabolites is investigated along with relative mixed function oxidase effects. Exposed liver tissues form benzo[a]pyrene proximate carcinogens even in the presence of lower microsomal activity especially in the presence of an inducer such as methylcholanthrene. Quantitative differences between adult and neonatal DNA enzyme systems are suggested for alkylated DNA repair.