To study the role of transforming growth factor-beta 1 (TGF-beta 1) in the pathogenesis of pulmonary fibrosis we have examined lung biopsies from nine patients with systemic sclerosis and interstitial lung disease, eight with 'lone' cryptogenic fibrosing alveolitis, two with cystic fibrosis, two with extrinsic allergic alveolitis, two with Langerhans' cell histiocytosis, one with lymphangioleiomyomatosis, one with giant cell interstitial pneumonia, and one adenocarcinoma of the lung. In cryptogenic fibrosing alveolitis, both 'lone' and associated with systemic sclerosis alveolar macrophages, bronchial epithelium and hyperplastic type II pneumonocytes expressed intracellular TGF-beta 1. Extracellular TGF-beta 1 was found in the fibrous tissue immediately beneath the bronchial and hyperplastic alveolar epithelium. In normal lung, however, the alveolar epithelium and alveolar interstitium were negative for both forms of TGF-beta 1. There was strong expression of TGF-beta 1 in hyperplastic mesothelium and its underlying connective tissue and in Langerhans' cells in the two cases of histiocytosis. In the organizing pneumonia in cystic fibrosis, the intraalveolar buds of granulation tissue reacted strongly for the extracellular form of TGF-beta 1 and the overlying hyperplastic epithelium expressed the intracellular form. In lymphangioleiomyomatosis, the aberrant smooth muscle cells strongly expressed intracellular TGF-beta 1 and the extracellular form was expressed in the adjacent connective tissue. In giant cell interstitial pneumonia, the numerous alveolar macrophage including the multinucleate forms, expressed intracellular TGF-beta 1, as did the hyperplastic alveolar epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)