The nose is a structurally and functionally complex organ. There are many conspicuous differences in the gross and microscopic anatomy of this organ among mammalian species. Because the nasal airways can be a target for many inhaled toxicants, it is important that toxicologic pathologists understand the normal nasal anatomy in laboratory animals commonly used in inhalation studies. In this brief review, species differences in gross anatomy, in nasal airway epithelia, and in the distribution and composition of the mucous secretory product are emphasized. In addition, the variance in surface epithelium throughout the nasal airway of one species is illustrated. The nasal surface epithelium varies in a) the types of cells present in various intranasal locations in the same species; b) the types of cells in different species in the same relative location; and c) the abundance and distribution of stored secretory product in different intranasal regions and in different species. This structural diversity translates into various functional differences and possibly into dissimilarities in the response to inhaled toxicants. Responsible estimates of risks of nasal toxicants to human health must be made with a knowledge of the differences and similarities of the structural components in human and animal nasal airways.