Xenobiotic substances are oxidatively metabolized in the hepatic tissue by microsomal monooxygenases of the cytochrome P-450 class and by flavomonooxygenases. The N-oxidation of amines in animals is a function of the hepatic flavomonooxygenases. Hepatic monooxygenase activities toward amines have become of particular concern 1 3 owing to the fact that people are increasingly subjected to numerous pharmacologically active nitrogen compounds (nicotine, tranquilizers, antihistamines, narcotics, hallucinogens, tropic alkaloids, ephedrine and derivatives, etc.) and the N-oxidation of arylamines and arylamides is a prerequisite in the conversion of these agents into their ultimate carcinogenic derivatives. © 1979, American Chemical Society. All rights reserved.