The enzymes relating to phosphoric acid metabolism, oxido-reduction system and carbohydrate metabolism were histochemically demonstrated in the Purkinje cells, right bundle branch, left bundle branch, and atrioventricular node. Generally, the enzyme activity in the tissue cells of the conduction system (CS) was lower than in the tissue cells of the heart muscle (HM). Only phosphorylase activity of the conduction system was higher than that of the heart muscle. The polyglucose particles synthesized by phosphorylase and brancher were larger and more numerous under the electron microscopic level in the CS. The activities of glucose-P isomerase, phosphoglucomutase and ribose-5-phosphate (R-5-P) isomerase were newly demonstrated in CS and HM. The activities of glucose-6-P-dehydrogenase (G-6-P DH) and R-5-P isomerase in the CS were the same as or slightly lower than their activities in the HM. The activities of G-6-P and succinate dehydrogenase in the CS were apparently lower than those in the HM. Acid-P and alkaline-P activities were very slight or almost negative in both CS and HM. Higher phosphorylase activity and considerable ATP, G-6-P DH and R-5-P isomerase activities in the CS are related to anaerobic metabolism and to the chemical energy from ATP and NADPH.