We used a questionnaire combined with medical history and spirometric studies to compare symptoms and respiratory function in two groups of subjects living in the French province of Doubs. A group of 250 dairy farmers was compared with 250 control subjects, matched with regard to sex, age, height, and smoking habits. The prevalence of acute bronchial infections and dyspnea was identical in the two groups. Among dairy farmers, 30 (12 percent) had chronic bronchitis vs 15 (6 percent) in the control group (p less than 0.05). Chronic bronchitis was more common in patients aged over 40 years (p less than 0.001) and in nonsmokers (p less than 0.001). All respiratory function parameters measured (expressed as a mean percentage of values measured in comparison with theoretic values) were lower in the dairy farmer group than in the control group. With regard to degree of bronchial obstruction, the difference between the two groups was more marked in patients aged 40 years and over and in nonsmokers. Dairy farmers' occupation is a risk factor of chronic bronchitis and bronchial obstruction, in particular in patients aged 40 years and over and in nonsmokers.