1. Microsomal and cytosolic drug-metabolizing enzyme activities of respiratory mucosa of male and female monkeys have been determined and compared to those of monkey liver. The results demonstrated that cytochrome P-450, NADPH-cytochrome P-450 reductase and some monooxygenase activities, especially ethoxycoumarin O-deethylase activity, were present in respiratory epithelium, although at lower levels than in liver.

2. Activities of non-oxidative enzymes—namely, epoxide hydrolase, UDP-glucuronyl-transferase, glutathione S-transferase, DT-diaphorase, carbonyl reductase, benzaldehyde and propionaldehyde dehydrogenases—were also detected in respiratory tissue, some at higher levels than in liver.

3. The enzymic activities found in monkey nasal mucosa are not very similar to those in corresponding human tissue where, for example, UDP-glucuronyltransferase activity is not detectable. This indicates that monkey is not necessarily the best animal model for studies of the human upper respiratory tract.