From 1973 to 1974, a longitudinal study of pulmonary function in 113 Utah copper smelter workers reported significant declines in FVC and FEV1 related to sulfur dioxide exposure. In 1980, we performed a 7-yr follow-up study, finding significant increases in FVC and FEV1. The 66 follow-up participants were similar to those 47 lost to follow-up with regard to age and initial pulmonary function. Subgroups of smelter workers with initial higher exposures to sulfur dioxide and FEV1 less than 90% predicted did not show an accelerated rate of decline. To reconcile these differences between the 2 studies, we reevaluated the spirometry curves from 1973 and 1974. All had short expiratory times, with none 6 s or longer, whereas all of the curves from the spirograms obtained in 1980 exceeded 6 s. In addition, from 1980 to 1983, we performed a longitudinal study of 48 of the original workers, finding small annual mean declines for FVC of 6 ml and FEV1 of 5 ml. Personal exposures to sulfur dioxide were not significantly different in 1982 than in 1976; thus, we were unable to corroborate the findings of the initial longitudinal study.