Despite the absorption of inhaled oxidant gases by the nasal cavity, little effort has been made to characterize the effects of these oxidants on the nasal mucosa. This study defines the effects of ambient concentrations of ozone on the character and amount of mucosubstances in epithelium of nasal mucosa. Bonnet monkeys were exposed to 0.00 or 0.15 ppm O3 (8 hr/day) for 6 or 90 days, anesthetized, and exsanguinated. Nasal cavities were fixed with Karnovsky's fixative, decalcified, and processed for light microscopy, and sections were stained with alcian blue (pH 2.5)/periodic acid-Schiff or high iron diamine. Volume densities of secretory material in nasal epithelium were determined with the use of a Quantimet 900 image analyzer. After 6 days' exposure there were significant increases in both acidic and neutral glycoconjugates stored in transitional and respiratory epithelium. After 90 days there was significantly less mucosubstance than at 6 days. Only in the transitional epithelium did the total and sulfated mucosubstance remain greater than that of controls. Nasopharyngeal epithelium was minimally affected after 6 days of O3 and unchanged after 90 days. It is concluded that exposures to ambient levels of O3 induce significant changes in the stored secretory product of nasal epithelium.