Polymorphic epithelial mucin (PEM), the protein product of the gene muc-1, is a surface glycoprotein that is produced by a range of normal epithelial cells, but has been shown to be expressed at high levels in a range of adenocarcinomas. It has not been investigated extensively in head and neck related tissues, and not at all in head and neck squamous cell carcinomas (HNSCC). This immunohistochemical investigation using two monoclonal antibodies to muc-1 represents a baseline study of 18 HNSCC. In 13 cases, the glycoprotein was expressed at varying levels, usually in keratinizing foci. Although less prominent, expression was also present to some degree in nine of 23 control specimens of non-neoplastic mucosa, mostly at an epithelial level early in the parakeratinization process. Both antibodies showed a pattern of staining. The cellular basis for muc-1 expression is speculative at present and although it is at a lower level than in adenocarcinomas, it may help to provide further insight into epithelial cell differentiation in squamous cell carcinomas.