in a study of byssinosis and small airway diseases, pulmonary function measurements including helium (7440597) and oxygen (7782447) flow volume curves were made on 470 cotton mill employees exposed to various dust levels. the employees in these cotton mills had been screened previously for pulmonary abnormalities, and some employees had moved to work areas with lower dust levels. results showed that there was no significant increase in bronchitis or byssinosis in the dust areas nor were there any significant decreases in the percentages of normal forced vital capacity (pfvc) or forced expiratory volume in 1 second (pfev1) in the dusty areas. these results differ from those reported from mills in which no previous pulmonary testing had been conducted. a strong smoking/tenure/dust exposure interaction on pfvc and pfev1 was found, with the long tenured, high dust exposure, smokers having the lowest pfvc and pfev1. there was no significant increase in small airways abnormalities with increased dust and smoking, but the mean change in the density dependence ratio is too small to have clinical significance