Expression of cytoskeletal proteins has been shown to be dependent on the differentiation status of the tissue. In the present study, expression of two cytoskeletal proteins normally present in terminally differentiated keratinocytes, namely cytokeratin types 10/11 and involucrin, were studied in different stages of tumour progression in the oral mucosa. Results showed that cytokeratins 10/11 and involucrin strongly correlated with the differentiation status of cells. High expression was observed in non-dysplastic hyperplastic epithelium as compared to normal, dysplastic and neoplastic epithelium. In addition, various grades of dysplasia showed an inverse correlation with expression of these proteins. Statistical analysis of the results also showed a negative correlation between the differentiation of upper spinal cells and the stage of tumour progression. It therefore appears that the proteins studied may be useful as markers for epithelial carcinogenesis.