The relationships of smoking and dust exposure to serum alpha 1-antitrypsin concentrations were studied in 1,131 male workers who were PiM phenotypes and who were employed in 4 different environments. In each work group, current smokers had higher concentrations than nonsmokers or ex-smokers. Among current smokers, concentrations were highest in those who smoked the most and for the longest time. Within the smoking categories the concentrations in most instances were greatest in workers exposed to the greatest dust concentrations. A significant positive relationship with duration of employment was found only in 1 work group. The independent effects of smoking and dust exposure persisted when the analysis was repeated using only nonatopic workers who were free of chest symptoms. Although both the biologic significance of these variations and the underlying mechanisms require clarification, the findings suggest that extrinsic factors, such as smoking and industrial dust exposure, may influence serum alpha 1-antitrypsin concentrations.