The hippocampal formation of the rat brain was studied by the Falck-Hillarp method and Karnovsky method after administration of dithizone, alloxan, and oxine. The purpose of this experiment was to clear the relation between cholinergic, adrenergic terminals and zinc in the mossy fiber synaps. The acetylcholinesterase and catecholamine reaction increased in oxine and dithizone administration. On the other hand, when dithizone and oxine were administrated, zinc decreased in the mossy fiber synaps. From this result, the relation between zinc in mossy fiber synaps and acetylcholinesterase, catecholamine in the hippocampus were discussed.