We performed a follow-up study of 61 patients who had an acute episode of farmer's lung (54 men and seven women). Twenty-four subjects had ceased all contact with the barn, while 37 had continued farming. Pulmonary function tests for all subjects showed an initial improvement after the acute episode: 92.4 +/- 36.9 percent of predicted for carbon monoxide diffusing capacity (Dco) after one year, compared to 61.5 +/- 28.5 percent at diagnosis (p less than 0.01); and 6.01 +/- 1.50 L for total lung capacity (TLC) after three years, compared to 5.35 +/- 1.42 L (p less than 0.05). Subsequently, pulmonary function decreased over time. Five years or more after the acute episode, pulmonary function tests in subjects who had continued farm work were not worse than those of subjects who had ceased contact for Dco (68.1 +/- 21.4 percent of predicted vs 80.6 +/- 27.7 percent, respectively [p greater than 0.1]) and for TLC (5.55 +/- 1.31 L vs 5.90 +/- 0.84 L [p greater than 0.2]). This study shows that during a long-term follow-up, subjects with farmer's lung who stayed on the farm have subnormal values for pulmonary function but comparable values to those who left their farm.