To test the hypothesis that asymptomatic farmers with serum precipitins to farmers' lung disease antigens also have an immune reaction involving the lungs, we did bronchoalveolar lavage (BAL) in 3 groups of dairy farmers. Group 1: 7 patients with acute farmers' lung disease. Group 2: 10 asymptomatic farmers with serum precipitins to Micropolyspora faeni. Group 3: 9 normal farmers without serum precipitins. Group 1 patients had a large number of cells (90.4 +/- 20 X 10(6)) (mean +/- SEM) with 72 +/- 5.8% lymphocytes in their lavage fluid. Their lavage also had high immunoglobulins A and G/albumin ratios. Six subjects in Group 2 had an increased number of cells (54.1 +/- 14.1 X 10(6)) and a high percentage of lymphocytes (52.5 +/- 6.6%) in their BAL. Two subjects in Group 3 had similar alterations in their lavage fluid: 60.0 and 69.6 X 10(6) cells with 20 and 37.5% lymphocytes, respectively. The other subjects in Groups 2 and 3 had normal lavages. Proliferative responses of BAL lymphocytes to phytohemagglutinin was similar in each group. Circulating immune complexes were increased only in subject with acute farmers' lung disease (Group 1). These results show that some normal farmers have signs of an alveolitis.