A group of 92 farmers had clinical evaluation, pulmonary function tests, and bronchoalveolar lavage (BAL). There were 12 patients with acute farmers' lung disease (FLD) (group 1) and 37 farmers who had had acute FLD, of whom 22 were still on their farm (group 2) and 15 had ceased contact (group 3); others were normal dairy farmers, 23 serology positive to Micropolyspora faeni (group 4), 20 serology negative (group 5), and 42 normal controls (group 6). Of the 134 subjects, 59 had an increase in alveolar lymphocytes (greater than 22% lymphocytes in BAL) (12 in group 1, 19 in group 2, six in group 3, 14 in group 4, five in group 5, and three in group 6). Within each group there was no correlation between BAL lymphocytes (% and absolute number) and most pulmonary function tests. It is concluded that although an increase in BAL lymphocytes is always seen in acute FLD it may also be seen in the absence of clinically evident disease and that BAL lymphocytosis does not correlate with physiological changes in FLD.