This study is a longitudinal comparison of the health of children exposed to markedly different concentrations of sulfur dioxide (SO2 and moderately different concentrations of particulate sulfate (SO4). The four groups of subjects lived in two areas of one smelter town and in two other towns, one of which was also a smelter town. In the area of highest pollution, children were Intermittently exposed to high SO2 levels (peak three-hour average concentration exceeded 2,500 μg/ m3 and moderate particulate SO2 levels (average concentration was 10.1 μg/ m3 When the children were grouped by the four gradients of pollution observed, the prevalence of cough (measured by questionnaire) correlated significantly with pollution levels (trend chi-square = 5.6, p = 0.02). No significant differences in the incidence of cough or other symptoms occurred among the groups of subjects over three years, and pulmonary function and lung function growth over the study were roughly equal among all the groups. These results suggest that intermittent elevations In SO2 concentration, in the presence of moderate partic ulate SO4 concentration, produced evidence of bronchial irritation In the subjects, but no chronic effect on lung function or lung function growth was detected.