Ultramicrochemical methods were used to assay lactic dehydrogenase (L.D.H.) activity in non‐ inflamed attached gingival tissue of dogs. Precautions were taken to insure the clinical and histological non‐inflamed status of the gingivectomy specimens. Frozen dried sections were dissected under a stereomicroscope into representative morphologically distinct fragments which ranged in weight from 12 to 240 nanograms (10−9grams). Quantitative results for the various strata of epithelium, connective tissue and whole epithelium were calculated. The mean L.D.H. activity was reported in micromoles per gram of dry tissue weight per minute at 37°C: surface layer, O; granular layer, 303; spinous layer, 613; basal layer, 801; connective tissue, 42; and whole epithelium, 574. These results are in agreement, for the most part, with L.D.H. activity assayed in other oral masticatory mucosal tissue, such as rat palate, which is less susceptible to chronic inflammatory process than is gingival