Two hundred nine male farmers engaged in swine production, born in 1913 or later, and alive in 1985 received mailed questionnaires on respiratory symptoms, medical history, and exposure to contaminated air in swine confinement buildings. The response rate was 76%. The prevalence of three or more symptoms of bronchitis was higher than that in welders who had completed the same questionnaire--Mantel-Haenszel odds ratio 5.26 (1.9-14.8) for smoking subjects. The number of reported symptoms was strongly influenced by smoking habits (p less than .01) and by exposure (p less than .01), and by a positive interaction between these (p less than .01, two-way analysis of covariance). Air in swine confinement buildings is contaminated with bacterial endotoxins and organic dust, and it is concluded that it may pose a risk for airways diseases such as chronic bronchitis.