Certain types of cells show a dramatic change in cell morphology cultured in the presence of transforming growth factor beta (TGF-β). To identify cellular components or factors leading to morphological changes, we investigated if any members of cytoskeletal proteins and cell-adhesion molecules were redistributed in TGF-β-treated Swiss 3T3 fibroblasts by indirect immunofluorescence and Western-blot analysis. Changes in cell morphology became apparent within 12h of the addition of TGF-β and new RNA and protein synthesis was necessitated by the changes. While TGF-β induced reorganization of microfilaments as reported in earlier studies, one of the actin isoforms, alpha actin of smooth muscle, was induced to form stress fibers in Swiss 3T3 cells. It was observed that myosin light chain was relocated from cell periphery to cytoplasmic filamentous structures by TGF-β treatment, with an increased amount. In addition, the cell-shape change was accompanied by an increase in the level of vinculin and tyrosine phosphorylation at focal adhesions. These results suggest that new protein synthesis is required for the cell-shape change, and acto-myosin filaments and focal adhesion proteins are involved in the alteration of cell morphology induced by TGF-β in Swiss 3T3 fibroblasts.