AbstractThe prenatal development of rodent nasal mucous membrane has been examined histochemically (lactate dehydrogenase, succinate dehydrogenase, glucose‐6‐phosphate dehydrogenase, alkaline phosphatase, PAS and PAS with diastase digestion). Localization and intensity of the enzyme systems studied were distinctly different in respiratory and olfactory areas. These differences were demonstrable by at least the second half of gestation in the animals studied. Findings in Jacobson's organs were parallel to those in olfactory areas. Each of the pathways of carbohydrate metabolism examined was present in respiratory epithelium. However, intensity was less, appeared later and was more variable in intracellular localization than that found in olfactory areas. Based on enzyme staining olfactory epithelium seemed metabolically more active than respiratory mucosa. Apical portions of olfactory epithelium stained most intensely for oxidative enzyme systems, particularly the glucose‐6‐phosphate dehydrogenase system. These areas of high activity were thought to represent apices of supporting cells rather than receptor cells. This localization of a pentose phosphate shunt enzyme system was related speculatively to ion transport in these cells. Alkaline phosphatase was relatively slight in respiratory areas during the ages studied. The basal portions of olfactory epithelium stained positively for alkaline phosphatase. Since hydrolytic enzymes have been thought to be important in the mechanism of olfaction, its demonstration in these tissues suggests that this portion of the olfactory mechanism is present by midgestation in the rodents