Mineral fiber-induced pleural mesothelioma in the rat is a suitable model for asbestos-induced mesothelioma in humans. A proposed mechanism for the genesis of mesotheliomas is the initiation of an autocrine pathway leading to unregulated growth of the mesothelium. To understand if changes in the expression of mRNA of critical growth factors and receptors occur in target mesothelial cells, it is first necessary to characterize the pattern of expression of these genes in normal mesothelial cells. Rat mesothelial cells were isolated from the parietal pleura and strains of these cells were propagated in vitro. The cells were diploid, had epithelial gross morphology and ultrastructure, and coexpressed keratins and vimentin. Northern blot analysis demonstrated that the cells expressed transforming growth factor beta 1 and fibroblast growth factor. Transcripts for transforming growth factor alpha, platelet-derived growth factor A-chain, and platelet-derived growth factor B-chain were not detected. Receptors for platelet-derived growth factor, epidermal growth factor, and insulin were detected. Although normal mesothelial cells express receptors for these growth factors, no production of their corresponding ligands by these cells could be detected, suggesting that autocrine stimulation of growth via the production of such factors may be specific to transformed mesothelial cells.