Subdividing the cheek, palate and ventral tongue into seven anatomically identifiable regions enabled us to assess relationships that were previously obscured by the great heterogeneity of rat oral epithelium. Capillaries were visualized by an alkaline phosphatase azo dye method in oral mucosa of four 3-month old male rats. Basal layer length per unit surface length showed a statistically significant relationship with the thickness of the epithelial cell layer in all seven regions. Linear regression of mean regional length of basal layer on mean thickness of the cellular layer in the seven regions was statistically highly significant. This was true also for mean capillary length. Thickness of the cellular layer, length of the basal layer and capillary length were similar in a palatal ruga and a thick region of cheek, suggesting that epithelial thickness rather than the type of mucosa influences the magnitude of these values. Proportional reductions in all three variables were observed in a second region of cheek and a region of ventral tongue, supporting this suggestion.