Glutathione (GSH), a major extracellular antioxidant, has been found in high concentrations in the epithelial lining fluid of the lower respiratory tract. The GSH concentrations in nasal fluid, in normal and pathologic conditions, were investigated and found to be very low. A GSH aerosol (600 mg daily for 10 days) increased GSH levels in the nasal mucosa and induced a statistically significant improvement in nasal obstruction, rhinorrhea, and ear fullness. Thus, GSH administered by aerosol could be a means of defending the epithelial respiratory cells against a toxic oxidant.