The Ki-67 nuclear antigen is associated with cell proliferation and found throughout the cell cycle; though not in G0 phase (1,2). The assessment of Ki-67 proliferation in breast cancers has shown the Ki-67 labelling index is an important predictor of survival (3). Cytokeratin (CK) 7 is expressed in epithelial cells of the ovary, lung and breast. Rabbit monoclonal CK7 (Clone BC1) is often used in conjunction with CK20 and CDX-2 in distinguishing pulmonary, ovarian and breast carcinomas (CK7 ) from most colon carcinomas (CK7-) (4). Clones EP17 and EP30 recognize CK8 and CK18, both of which recognize low molecular weight intermediate filament proteins. In normal tissues, CK8/18 recognizes all simple and glandular epithelium (5). In neoplastic tissues, CK8/18 may prove useful for the identification of most adenocarcinomas and some squamous cell carcinomas. CK8/18 expression patterns may also aid in the classification of tumors of unknown origin and poorly differentiated carcinomas (5-7). CK8/18 rabbit monoclonal may be useful as a staining mask in a multiplex stain with mouse monoclonal antibody Ki-67.