The interrelation between leukocyte count, cigarette smoking, and pulmonary function results was examined in two work populations: 1,826 white male workers in a pulp and paper mill and 1,620 white male workers in an aluminum smelter in British Columbia. These workers took part in epidemiologic health studies that consisted of a medical-occupational questionnaire, spirometric measurements, and leukocyte count. Measurements of the air contaminants in the work environment were also carried out simultaneously by personal and area sampling. No significant increase in the prevalence of respiratory symptoms and lung function abnormalities was found between the exposed and nonexposed workers in each work population. Similarly, no difference in leukocyte count was found between exposed and nonexposed workers. Leukocyte count was found to be significantly higher among current smokers than nonsmokers and former smokers in each population. In both populations, there was an inverse correlation between leukocyte count and one-second forced expiratory volume and forced vital capacity of the workers irrespective of the smoking habit. This finding suggests that the leukocyte response to external stimuli may be another determinant of lung function measurements.