The present investigation was undertaken to study the carbohydrate metabolism of the mesencephalic nucleus of the trigeminal nerve in detail: The latest histochemical methods were applied to the rat brain. The nerve cells of the nucleus showed variable reactions in their cytoplasm for enzymes: The reactions were moderate through the modified Takeuchi-Kuriaki method; either strong or negative through Friede’s method for amylophosphorylase; moderate or strong for aldolase, succinate dehydrogenase and cytochrome oxiclase; weak or moderate for glucose-6-phosphate dehydrogenase and weak for 6-phosphogluconate dehydrogenase. The neuropile showed weak or moderate reactions through the modified Takeuchi-Kuriaki method. It exhibited the slight reactions for aldolase, and for glucose-6-phosphate, 6-phosphogluconate and succinate dehydrogenases as well as the weak reaction for cytochrome oxidase. Some satellite cells showed strong amylophosphorylase reactions through Friede’s method, moderate ones through the modified Takeuchi-Kuriaki method, and moderate aldolase reactions, while the reactions for succinate dehydrogenase and cytochrome oxidase appeared to be weak. Weak reactions were observed in the nuclei of the nerve cells for these enzymes. There was no perinuclear concentration of succinate dehydrogenase or of cytochrome oxidase.