Biopsies from 13 oral leukoplakias and from normal tissue specimens in the contralateral region of each patient were examined histologically and microradiographically. Microradiographs of freeze-sectioned and freeze-dried sections were made and quantitative photometric analyses of the distribution of the dry mass concentration in different epithelial cell layers of both normal and pathologic specimens were performed. In each microradiograph, the thickness of the stratum corneum was determined. The results indicated that in oral leukoplakia two main changes occur in the epithelial surface layer, i.e. an increase of the thickness of the surface epithelial cell layer, and a formation of an epithelial surface zone of cell layers with different degrees of keratinization and varying dry mass concentrations.