2 cases of hereditary palmoplantar keratoderma (Unna-Thost type and keratosis palmoplantaris striata s. linearis type) are reported. In the former, moderate hyperkeratosis and a partial decrease in the stratum granulosum were histologically seen. Keratohyalin granules in the uppermost cell layer of the stratum granulosum were positively stained with the Pauly reagent, though the stratum granulosum consisted of three of four cell layers in the hematoxylin-eosin-stained specimen. Electron microscopically, keratohyalin granules in the lower two or three cell layers of the stratum granulosum were less electron-dense than normal and were granular in appearance, but those in the uppermost cell layer were normal in electron density and in appearance. This case indicates that human keratohyalin granules could consist of a less electron-dense component and an electron-dense amorphous component, and the Pauly-positive substance could be electron-dense and amorphous, and the basophilic material in the hematoxylin-eosin specimen could be less electron-dense and granular under electron microscopy. In the latter, remarkable orthokeratotic hyperkeratosis and hypergranulosis were observed. Electron microscopically, three kinds of keratohyalin-like granules were observed: (1) less electron-dense granules, the electron density of which was equivalent to that of the peripheral region of the nucleus; (2) normally electron-dense amorphous granules attached to the first type of granule, and (3) extremely less electron-dense granules with a finely granular appearance. The diameter of this finely granular material was around 21 nm and a fibrous structure was also observed in or attached to this granule.