Lung function, bronchial reactivity, serum antibody levels, bronchoalveolar lavage (BAL) fluid and the magnitude of exposure to airborne microorganisms during farm work were studied in 10 healthy farmers with no respiratory symptoms. Lung function and bronchial reactivity were not altered. An increase in the amount of antibodies against several microorganisms could be demonstrated but precipitating antibodies were observed only in two subjects. In the BAL fluid the nonsmoking farmers had elevated proportion of lymphocytes and elevated levels of albumin, fibronectin and angiotensin-converting enzyme while the levels of hyaluronan and procollagen III N-terminal peptide were within normal limits. The lung function, bronchial reactivity, serum antibody levels and BAL findings were not correlated with the exposure to airborne microorganisms. We conclude that healthy farmers, exposed to mold dust, may exhibit signs of alveolitis including albumin leakage, accumulation of inflammatory cells and alveolar macrophage activation.