Reacts strongly with cytokeratins 5 and 6 and weakly with cytokeratin 4. The antibody does not cross-react with cytokeratins 1, 7, 8, 10, 13, 14, 18 and 19. It labels mesothelioma, and epithelial basal cells in prostate and tonsil. No reactivity with other mesodermally derived tissues, such as muscle and connective tissues, has been observed. The antibody is a useful aid for classification of epithelioid mesotheliomas.