Vimentin is the major subunit protein of the intermediate filaments of mesenchumal cells, and has a molecular weight of 57kD. Immunohistochemical staining for Vimentin is thus characteristic of sarcomas (of neural, muscle and fibroblast origin) compared to carcinomas which are generally negative. Melanomas, lymphomas and vascular tumors may all stain for Vimentin. Vimentin antibodies are thus of value in the differential diagnosis of malignant tumors, generally used with a panel of other antibodies including those recognizing cytokeratins, lymphoid markers, S100, desmin and neurofilaments. The antibody stains the 57kD vimentin band in immunoblots performed on a lysate of normal human lymphocytes. It does not stain mouse or rat vimentin.