Sulfuric acid (H2SO4) aerosols are common in both ambient and occupational environments. This study examined the numbers and selected in vitro functional properties of alveolar macrophages recovered from rabbits undergoing inhalation exposure to 0.5 mg/m3 submicrometer (0.3 micron) H2SO4 for 2 hr/day. Bronchoalveolar lavage was performed on Days 3, 7, and 14 during the exposure period (specifically, 24 hr after either 2, 6, or 13 exposures). Total cell numbers and macrophage counts were increased on Day 3, but returned to control levels by Day 7; no change in polymorphonuclear leukocytes was observed at any time point. Macrophage substrate attachment was not affected by exposures to H2SO4, but random mobility was severely depressed at Days 7 and 14. The numbers of phagocytically active macrophages and the level of such activity were increased on Day 3, but became depressed by Day 14. These results demonstrate significant alterations in important functional properties of alveolar macrophages due to short-term intermittent exposures to H2SO4 aerosols; these changes have implications for the ability of the lungs to maintain adequate defense against deposited viable and nonviable particles.