The drug-metabolizing enzymes of olfactory and respiratory epithelium of cattle were determined. The data of nasal tissues were compared to those of bovine liver. Both oxidative and nonoxidative enzyme activities were investigated. Many compounds including testosterone were used as substrates for the P450-dependent monooxygenase activities. The results demonstrated that the P450 content and all the activities assayed including reduced nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome P450 reductase were much higher in the olfactory than in the respiratory mucosa and for some activities (hexamethyl-phosphoramide and dimethylnitrosamine N-demethylase, aniline hydroxylase, and ethoxycoumarin O-deethylase) the values in the olfactory tissue were even markedly higher than those of liver. Also the activities of some nonoxidative enzymes such as glutathione S-transferase, uridine 5'-diphosphate (UDP)-glucuronyl-transferase, and epoxide hydrolase were higher in the olfactory than in the respiratory mucosa but lower than in liver. The results taken together suggest that the olfactory and respiratory epithelium of cattle, which contain in addition to a wide array of nonoxidative enzymes multiple forms of P450, can be useful and easily available tissues to study the biotransformation processes of odorants.

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