SummaryAutoantibodies to nuclear and cytoplasmic constitutents and to denatured γ‐globulin have been studied in patients with different types of chronic fibrosing lung disease. The prevalence of these antibodies is increased in cryptogenic fibrosing alveolitis but the incidence in extrinsic allergic alveolitis is similar to previous published reports on random populations and a control group included in this series of asbestos workers with normal chest radiographs. In asbestosis there was a lesser increase in ANF and rheumatoid factors but no significant increase in antibodies to cytoplasmic constituents. No evidence of organ‐specific autoantibodies to lung have been demonstrated in any group. The presence of non organ‐specific autoantibodies cannot necessarily be attributed to a non‐specific consequence of all types of chronic destructive pulmonary fibrosis because of their differential distribution in different lung diseases.Because ANF and RF but not precipitins to organic dust are positive in some 60% of patients with cryptogenic fibrosing alveolitis, and precipitins but not autoantibodies are found in chronic extrinsic allergic alveolitis, tests for these two groups of antibodies are complementary in the investigation of patients with widespread chronic radiographic shadows. Tissue antibodies were absent in 40% of patients with cryptogenic fibrosing alveolitis and a more detailed search for other types of antigen should be made in the