Abstract— Sections of seven typical grayish-white leukoplakias from the gingiva of the hard palate. the inside of the lip, and of the cheek have been studied by means of ultra-soft X-ray historadiography. Conspicuous differences in keratinization were observed in the different biopsies. Apart from orthokeratinization and regular parakeratinization, two types of incomplete parakeratinization were observed. Historadiographs of paraffin sections have been compared with hematoxylineosin and van Gieson-Hansen stained adjacent sections. The highest dry weight was found in orthokeratosis and regular parakeratosis. In incomplete parakeratosis flattened cells of the keratinized layer showed, in most cases, considerably higher dry weight than unflattened cells. No correlation was found between the thickness of the stratum granulosum and the radiopacity of the stratum corneum. The investigation indicates that the process of keratinization of oral mucosa is not only a chemical process but comprises a loss of water and/or water-soluble substances as well.