Cytokeratin 7 is a basic filament protein, which is exprimed by many epithelial cells, especially those of the ductal and glandular types. The antibody doesn't react with squamous epithelia but with transitional cell epithelia of the urinary tract. Epithelia of the lung and breast are positive while colon and prostate remain unstained. The antibody is helpful for the differentiation of colon and ovarian cancer cells in ascites. Cytokeratins are a group of water soluble filament proteins, which are components of the cytoskeleton of the epidermis and other epithelial cells. Gel-electrophoretic investigation revealed 20 different Cytokeratins, characterised by different molecular sizes and pI-values. They can be subdivided into basic and acid subfamilies. The nomenclature according to Moll et al. (1982) is most commonly used. Basic Cytokeratin, 54 kD, CK 7 (Moll).