The electron-microscopic changes in the buccal epithelium were investigated in male Sprague-Dawley rats placed at weanling age for a 45 days period on a zinc-deficient diet and their controls on complete diet. Nutritional zinc deficiency caused hypertrophy and hyperplasia of the buccal epithelium and conversion from the normal ortho to parakeratosis. The prickle and granular cell layers revealed increase in cell size. The nuclei were enlarged, mitotic activity was increased and cell organelles were more concentrated with apparent dilatation and distinction of the rough endoplasmic reticulum. Marked perinuclear aggregation of tonofilaments together with the intracytoplasmic desmosomes were of the most striking findings. The membrane-coating granules showed increased number per cell, while the displacement of these granules to the periphery was decreased. These results indicated that zinc deficiency leads to increase capacity of the buccal epithelium for protein synthesis and, to dyskeratosis. This stresses the importance of zinc in the process of epithelial maturation