A role for transforming growth factor-beta 1, (TGF-beta 1) has been proposed in lung development and in the pathogenesis of pulmonary disease. However, previous studies have not delineated the cells expressing TGF-beta 1 in normal adult lung, nor compared its gene expression with that of other TGF-beta isoforms. We used digoxigenin-labelled riboprobes to localize TGF-beta 1 and TGF-beta 3 gene expression in normal adult human and mouse lung. This procedure was technically simple, providing excellent resolution. TGF-beta 1 and TGF-beta 3 messenger ribonucleic acid (mRNA) transcripts were detected in a wide variety of cells. In human lung, mRNA for both isoforms was localized to bronchiolar epithelium and alveolar macrophages. TGF-beta 1, but not TGF-beta 3 mRNA was detected in mesenchymal and endothelial cells. In murine tissue, TGF-beta 1, mRNA was localized to bronchiolar epithelium, Clara cells, mesenchymal cells, pulmonary endothelium and alveolar cells, including macrophages. TGF-beta 3 mRNA was similarly distributed but not detected in endothelium. In summary, using a nonisotopic technique in lung tissue, we have detailed the cells expressing the transforming growth factor-beta 1 and beta 3 genes in human and murine lung. There was widespread expression of these cytokines in normal lung consistent with autocrine or paracrine roles in regulating cellular turnover, immune defence and matrix protein metabolism.