We investigated normal oral epithelium and 20 oral squamous cell carcinomas with antibodies against oncogene products (p21, EGF-R) and intermediate filaments (cytokeratins 4, -10/11, -13, -18, Vimentin). Antigen expressions in oral epithelium and squamous cell carcinomas were associated in different patterns with epithelial maturation. Dedifferentiation of the squamous cell carcinomas was accompanied by quantitative changes in the oncogene products and a more complex pattern of the cellular intermediate filament equipment.