As the distribution pattern of cytokeratin (CK), filaggrin and involucrin has recently been suggested to discriminate between benign and malignant epithelial growths, biopsies of healthy oral mucosa, leukoplakias without and with dysplasia and squamous cell carcinomas were examined immunohistochemically using a panel of 4 monoclonal antibodies (AB) against different cytokeratin polypeptides (34 beta E12, KL1 and Pkk1) and filaggrin as well as a polyclonal AB to involucrin. Major and statistically significant differences were observed in the profiles of CKs (except Pkk1), filaggrin and involucrin between leukoplakias without and with epithelial dysplasia. However, the alteration in the expression of CKs, filaggrin and involucrin proved to be not a constant feature in leukoplakias with dysplasia as a considerable portion (20-25%) of them revealed the profiles of CKs, filaggrin and involucrin similar to those of benign leukoplakias, and vice versa. Immunostaining of these antigens did not define the diagnosis of dysplasia in leukoplakias more precisely than grading in conventional histology can do so far. However, immunohistochemical sensitivity in detecting a broad range of variation in the abnormal maturation patterns of keratinocytes in leukoplakias with dysplasia can be used to divide these lesions into subgroups to elucidate their prognosis in follow-up studies.