Cheek pouches were removed from 9 BIO 87.20 adult-male hamsters, pinned out on cork sheets and fixed, then divided into segments and processed. Mallory stain showed complete orthokeratinization of the pouch epithelium with regular keratohyaline granules. With scanning electron microscopy, the morphology of the walls was similar, with ridged areas alternating with flatter areas. In all areas, blunt projections and larger dome-shaped elevations were found. The superficial surfaces of all stratum corneum cells were covered by an interconnecting network of ridges surrounding depressions; their deep surfaces were covered by a complementary array of protuberances separated by narrow grooves. On superficial surfaces in some areas, cell boundaries consisted of double ridges separated by a gap; cell imprints were delineated by single ridges or depressions and involved several cells, suggesting that the cells in these areas were not stacked in vertical columns. Elsewhere, the linear ridges were paralleled by depressions, suggesting that the cells were stacked in columns. The morphology of cell boundaries and imprints on the undersurface of the desquamating squames were complementary to those of the opposing surface. Transmission electron microscopy supported the findings. Although most of the cells of the stratum corneum were electron dense and contained only tonofilaments and interfilamentous material, less electron-dense cells which contained only tonofilaments and small keratohyaline granules were occasionally found.