In connection with the chronic bronchitis key program of the German Research Society 1501 workers in a Munich engineering plant with foundry were examined from 1965 to 1970. With increasing exposure to dust at the work place, bronchitic symptoms such as coughing and sputum become significantly more frequent. Obstructive ventilation disturbances do not increase. Heavy smokers show an overwhelmingly greater frequency of bronchitic symptoms than those exposed to excessive dust. The increase in bronchial obstruction in relation to the consumption of tobacco is remarkable. The effect of age seems to be rather less than that of smoking and greater than that of dust.