Previous studies by us and by others have shown that the body weight of rats fed a zinc-deficient diet is significantly lower than that of pair fed controls, but marked hyperplasia and parakeratosis are seen intra-orally in the buccal epithelium. No histologic changes occur in palatal epithelium. This investigation was undertaken to assay lactate dehydrogenase (LDH) activity in the buccal and palatal epithelium in rats fed a zinc-deficient diet. Weanling male Simonsen rats were fed a diet containing 1.2 ppm zinc for a 30-day period. Pair fed controls were fed the same diet containint 40 ppm zinc. LDH levels were determined by ultramicrochemical assay. In the buccal epithelium, a more than twofold increase over that of controls was observed in zinc-deficient rats, but there was no change in the palatal epithelium. Thse results support the conclusion of others of an organ-specific sensitivity of LDH to zinc deprivation. No increases in LDH activity in zinc-deficient rats, as observed in the hyperplastic buccal epithelium in this study, have previously been reported.