A survey was made of 1317 men aged 40 to 65 years who were working full time in the Detroit area. A questionnaire, chest roentgenogram, and spirogram were obtained on each person. These men were divided into 4 categories: (1) no industrial exposure, 175; (2) industrial but no silica exposure, 598; (3) silica exposure for more than 20 years, normal chest roentgenogram, 404; (4) silica exposure for more than 20 years, roentgenogram showed silicosis, 140. Bronchitis, which was defined as the production of at least 1 teaspoon of sputum daily for the preceding 6 months, occurred in 17.4% at the age of 40 to 44, rising to 24.7% at the age of 60 to 64. The over-all prevalence of bronchitis in each of the above groups was 34.8, 22.6, 15.6, and 31.5%, respectively. The influence of increasing age, occupation, dust exposure, and cigarette smoking is considered. Cigarette smoking appears to be the most important factor in the etiology of chronic bronchitis in this selected group of the male population.