Seven healthy male volunteers were exposed through a face mask to SO₂ (12-13 ppm), NO₂ (14-17 ppm), and the mixture of both gases for 1 hour. Interval between each exposure was approximately 1 week. Immediately before and after the exposure, FEV_1.0, C_aw (body plethysmo-graphic method) and D_LCO (single breath technique) were measured. There was a subject whose C_aw/FRC responses were relatively high as compared with other subjects in all the exposures. In 4 subjects, relatively large reductions in C_aw/FRC after the exposure to the mixture were observed as compared with its changes by exposure to either SO₂ or NO₂ alone. After the exposure to SO₂-NO₂ mixture, the mean of the reduction in C_aw/FRC was 0.05 sec^-1. cmH₂O^-1. that was statistically significant, and, although it tended to decrease, the average change in D_LCO was not significant.