The respiratory effects of trona (533960) dust were evaluated in an epidemiological study. A total of 230 individuals (including 125 workers from a 1976 NIOSH study, and 32 with trona dermatitis) volunteered to participate in the study. They included 142 workers from underground and 88 workers from surface jobs at a company involved in trona mining. Referents were 125 nonexposed men. Exposure determinations included total work years, exposure categories, and cumulative trona dust exposure index. Each worker was asked to code his job according to level of trona or soda-ash exposure. Results showed no significant differences between underground and surface mean values, although surface spirometry values were lower. There were no differences in mean percentage of predicted spirometry values according to high, medium, or low exposure categories. Workers in the low category were significantly older and had a significantly greater duration of exposure. In workers tested before and after the workshifts, the forced expiratory volumes per second (FEV1) declined, and were significant in the surface workers and nonsmokers, and approached significance in those of the high exposure category. Only one of the 43 workers in the shift study had a 1% decline in the percentage of predicted FEV1 in both longitudinal and shift studies. A cross sectional study of annual changes in FEV1 by age, and work years, according to smoking habits showed a decline in FEV1, but followup showed a mean increase if they were nonsmokers or exsmokers. Of the study population 23% had chronic cough (33% smokers, 21% nonsmokers, 33% with dyspnea), 48% had nasal drainage, and 25% showed signs of mucous membrane inflammation. Respirable dust levels were 98mg/m3 versus the recommended threshold limit value of 10mg/m3. Underground levels were significantly higher than surface levels. The authors conclude that ventilatory function is relatively normal in workers exposed to trona dust, but significant declines are seen after a work shift, with increasing age, and in smokers.