To assess short term toxicity of aerosols generated from acidic (pH=3) and neutral (pH=6) sodium sulfite (Na2S2O5) solutions, 3 groups of rats were exposed to airborne concentrations of 50 mg/m-3 sulfite aerosol in a whole body exposure chamber. Acidic aerosols also contained 15-20 mg/m-3 SO2 gas. Two groups were exposed for 3 h to an acidic or a neutral aerosol, and the last group was exposed for 24 h to an acidic aerosol. Each aerosol had a mass median aerodynamic diameter of 1.1 μm and GSD of 2.1. After 3 h of exposure to neutral sulfite aerosol, the nasal epithelium had evidence of mild injury, whereas after 3 h of exposure to acidic aerosol, necrosis of the anterior nasal epithelium appeared. After 24 h of acidic sulfite aerosol exposure, necrosis of the epithelium throughout the nasal turbinates occurred accompanied by an infiltration of neutrophils. This injury by acidic sulfite aerosols correlated with very low activity of sulfite oxidase in rat nasal tissue. Although no histologic changes were found in the lung parenchyma, alveolar macrophages isolated from rats exposed to 24 h of acidic sulfite aerosol showed a reduction in their oxygen consumption by 50 %. Therefore, acidic sulfite aerosols cause marked injury to the nasal epithelium but have subtle effects on the lung parenchyma.