Lu-5 recognizes all subtypes of cytokeratins in cryofixed and paraffin sections and is ideally suited as a first order pan-epithelial marker. The epitope recognized by Lu-5 is a formalin-resistant marker of great value in tumor diagnosis, located on the surface of cytokeratin filaments. It has been preserved during vertebrate evolution and can be shown in all species from amphibia to man. The epitope is present in most cytokeratin polypeptides of both the acidic (type I) and basic (type II) subfamily but does not occur in other cytoskeletal proteins. The epithelial specificity and the broad tissue and species cross-reactivity provide an excellent probe for the differential diagnosis of epithelial versus mesenchymal tumours, large cell lymphomas and neural tumours. The antibody produces a brilliant staining even at high dilutions. Application: IHC (f, p)