A nested case-control study was carried out on a previously studied cohort. Members of the cohort were resurveyed in the first year of the study. All participants received a routine physical examination, chest x-ray, electrocardiogram if over 40 years of age, routine laboratory tests, methacholine challenge, intradermal skin testing, and bronchoalveolar lavage. Cases for the swine confinement farmer cohort were selected if they had FEF50 of 60 percent or less of predicted for age, sex, height, and race. Three referents for each case were randomly selected from all swine confinement farmers not selected as cases, non-confinement farmers, and blue collar workers. Measurements were repeated in the fourth year, finishing in the fifth year of the study. The study determined: the extent to which epidemiological studies underestimated pulmonary responses and impairments among agricultural workers; the environmental risk factors significantly related to cases; whether atopy and heightened airway reactivity were significantly associated risk factors. The subproject was not renewed in 1992.