Abstract The general fine structure of the hamster cheek pouch epithelium is described. A thin homogeneous basement membrane about 360 A in width separates basal cells from dense, randomly arranged collagen fibres in the adjacent lamina propria. The basal cells and stratum spinosum contain a profusion of fine granules and tonofibrils. Desmosomes appear throughout the various cell layers. Numerous well-preserved mitochondria with transverse cristae are identified in the basal cells, stratum spinosum and stratum granulosum of the cheek pouch epithelium. In the stratum corneum they occur less frequently and when seen, appear disintegrated. Small, very dense granules about 0.1 μ in diameter are seen in the cytoplasm of the upper stratum spinosum and stratum granulosum cells. Their function is unknown. Densely compacted tonofibrils appear to be the principal intracellular constituent of the cornified layer.