The purpose of this study is to determine and to compare the role of cytoskeletal proteins in epithelial cells during cell transformation by chemical and biological carcinogens. The effects of ethionine, a liver cell carcinogen, are evaluated in vitro and initial studies suggest deviations in cytoskeletal architecture concomitant with altered membrane fluidity in the course of transformation. In vivo experiments, using the Moloney virus-induced lymphoma as a model, are utilized to elucidate the mechanism of the differentiation block in the thymus resulting in generalized malignant lymphoma. Studies concentrate on thymic tissue and isolated thymic cells with special emphasis on the thymic epithelial cell and its microfilament/microtubule distribution.