[en] Ten healthy nonsmokers inhaled H₂SO₄ at 0 (control), 110, 330, and 980 μg/m³ for one hour via nasal mask in random sequence on four separate days. Respiratory mechanical function was assessed before and after the H₂SO₄ exposure. A /sup 99m/Tc tagged Fe₂O₃ aerosol was inhaled approx. 10 min before each H₂SO₄ exposure. Thoracic retention of the deposited radioactivity was monitored using collimated scintillation detectors. A tracheal probe was used to determine the tracheal mucociliary trnsport rates (TMTR's) of local concentrations of activity. Bronchial mucociliary clearance was markedly altered in a dose dependent pattern in six of the individuals and in the group as a whole. The four individuals whose clearance times were not significantly affected by these H₂SO₄ exposures were each given an additional test with a 1000 μg/m³ H₂SO₄ exposure preceding the tagged Fe₂O₃ aerosol. Three of them responded. Thus, 9 of 10 subjects had substantial changes in bronchial clearance times following H₂SO₄ exposures