These experiments have shown that human mesothelial cells as compared to fibroblasts are more sensitive to induction of structural chromosomal aberrations by exposure to asbestos fibers. In addition, it has been shown that malignant mesothelioma cell lines produce TGF-beta and PDGF-2 chain message while normal primary mesothelial cell cultures respond to mitogenic stimuli from the protein products of these messages. These findings suggest the possibility of an autocrine mechanism for the generation of mesothelioma. Two dimensional gel analysis of normal human bronchial epithelial cells after TPA or TGF-beta treatment has indicated several protein alterations which might correlate with squamous differentiation. The magnitude of the alterations is not great, implying that this technique may not display the most critical changes. It is of interest that Northern blot analysis indicates that a 2 hour treatment of human bronchial epithelial cells with TPA but not TGF-beta can induce an increase in IL-1 beta.