Guinea pigs will be exposed acutely to combinations of SO2 and NaCl aerosol at high and low relative humidity (RH), to which the following variables will be added: cold, heavy metal catalysts, increased ventilation. Pulmonary mechanics will be measured to determine the response. The experiments will be repeated in healthy volunteers. Guinea pigs will be exposed semi-chronically to combinations of SO2 and NaCl at high and low RH. Flow resistance will be measured periodically. The lungs will be removed at autopsy and studied by light and electron microscopy. The effects of ozone and irritant aerosols on the enzymatic composition, function, and structural appearance of respiratory mitochondria will be studied. Studies will be done on rabbits.