The prevalence of nonspecific respiratory symptoms in workers exposed to asbestos (13322143) during asbestos mining and processing were examined. An assessment was made of lung function and radiological changes in these workers. Emphasis was placed on establishing a relationship between the concentration of airborne dust, the length of exposure and the total exposure with the pulmonary impairment which the worker suffered. The study was conducted at two mines, two factories producing asbestos cement products and one factory manufacturing asbestos textiles and friction materials. Examinations were made of 1,242 asbestos workers and a comparison group o 1,950 workers. Each respiratory symptom analyzed was more common in males than in females and in smokers than in nonsmokers. In 41 of 897 men, asbestos bodies were recorded. The presence of asbestos bodies was not related to age, duration of exposure or to the total exposure level. All the symptoms found were much less related to asbestos fiber years than to total particle years of exposure. Radiological findings indicated that only the prevalences of small opacities increases more or less consistently with the duration of exposure to asbestos, asbestos fiber years and total particle years. Some evidence was found of a harmful effect of simultaneous smoking and exposure.