 (1990) compared the effects of fetal versus adult exposure to 3-MC on both induction of aryl hydrocarbon hydroxylase (AHH) activity in lung and dependence of lung tumorigenesis on the Ah genotype.A single ip injection (in inducible fetal lung supernatants) of 100 mg/kg of 3-MC to the mothers resulted in a maximal 50-fold induction of AHH activity by 8 hr, which persisted for 48 hr.The same injections to adult F1 mice revealed only a 4- to 7—fold increase in lung AHH activity, compared to the large fetal induction ratio.