Forty cases of nasopharyngeal neoplasia were analyzed using immunohistochemical staining employing keratin antibodies. Using this probe the tumors were classified as being keratin-positive or negative. In this study, all squamous cell carcinomas labeled with keratin antibodies whether they were classified as keratinizing or nonkeratinizing by usual staining methods. In contrast, lymphoid and mesenchymal tumors of the nasopharynx did not label with keratin antibodies. Thus, the presence of keratin proteins as detected by immunohistochemical means on paraffin-embedded tissues appears to be a useful, reliable, and sensitive method for aiding in the accurate diagnosis and classification of nasopharyngeal neoplasms.