The effects of sulfur oxide pollutants on respiratory function, particle deposition, and bronchial clearance were explored in a series of three studies, two on donkeys and one on humans. In the first study, the effects of one-hour inhalation exposures to 0.3 - 0.6 micrograms H2SO4 and (NH4)2SO4 aerosols in the donkey were studied in terms of alterations in pulmonary flow resistance and dynamic compliance, and changes in the regional deposition and tracheobronchial mucociliary clearance of an inert test aerosol. In the second study, the effect of chronic inhalation exposures to sulfuric acid mist upon mucociliary clearance from the lungs was studied, using the donkey as an analogue for man. Four animals were exposed one hour per day, five days per week, for six months; two to a concentration of 102 micrograms/cu m, the other to 106 micrograms/cu m. In the final study, the mucociliary particle clearance and respiratory mechanics of twelve healty nonsmokers exposed to 1/2 micrometer H2SO4 at 0 (control), 100, 300, and 1,000 micrograms/cu m for one hour per day for four days were examined.