The influence of occupational work exposure and host factors on the incidence of dyspnea and wheezing as reported in questionnaires was examined in 1,301 new employees in aluminum electrolytic potrooms. The incidence appeared to decrease after 2 yr of exposure, and the estimated probability of development of symptoms was nearly 20% after 4 yr. A total of 105 subjects developed dyspnea and wheezing. Of 78 symptomatic subjects who were interviewed, 76% experienced improvement or absence of symptoms when off work. In 523 subjects who were assigned to specific levels of exposure at the end of follow-up, a dose-response gradient was found between the development of symptoms and fluoride exposure. Increased risk with increasing amounts of tobacco was also observed, but childhood allergy and a family history of asthma were not significantly related to the outcome variable. We conclude that both total fluoride exposure and smoking are related to asthmatic symptoms in potroom workers, and the suggestion of a dose-response gradient was found for both variables. However, a causal relationship between fluorides and symptoms should be investigated further by specific bronchial provocation testing and by research for specific antibodies and other immunologic markers.