Biopsies from normal and inflamed human gingiva were frozen and sectioned and then incubated for the demonstration of DPNH and TPNH diaphorases, succinic, lactic, glutamic, isocitric, malic and glucose‐6‐phosphate dehydrogenases. Aerobic enzyme activity was found to be maximal in the basal cell layer decreasing to the surface of both the keratinizing oral and the non‐keratinizing crevicular epithelium. Anaerobic enzyme activity was found to be maximal in the upper prickle cells. No difference in formazan deposition was seen in the oral and crevicular epithelium of normal and inflamed specimens. The enzyme activity of desquamating cells of the crevicular epithelium, however, showed a slightly different pattern. In addition to a general perinuclear formazan deposition in active epithelial cells, areas at the cell periphery corresponding to desmosomes showed an accentuated formazan deposition with all the enzyme systems investigated. The similarity of this distribution of formazan in sections incubated for endogenous reducing activity was tested. The significance of these findings is disc