The nasal epithelia in several species contains fairly high levels of drug metabolising enzymes, and in many cases the site specific toxicities of chemicals are due to their metabolic activation in the nasal tissues. This article reviews some of the current literature on the metabolic capacities of nasal epithelia, in particular the distribution and characteristics of cytochrome P-450 isozymes. In addition to the role of these nasal enzymes in metabolism of inhaled xenobiotics, other possible biological roles for these enzymes are also discussed.