1. It having previously been shown that the injection of the non‐metabolizable sugar, 3‐methylglucose, into normal rats provokes the release of adrenaline with consequent hyperglycaemia, the effect of 3‐methylglucose upon the metabolism of glucose was investigated. In rats, whose adrenal glands had been denervated by transplantation, 3‐methylglucose reduced the oxidation of glucose by 46%. A reduction of this magnitude cannot be accounted for unless the oxidation of glucose by the brain is depressed.2. The lowering of the blood glucose concentration of adrenalectomized rats by insulin was prevented by the prior administration of 3‐methylglucose.3. 3‐Methylglucose retarded the movement of a glucose load from the blood into the tissues.4. The results of these experiments are consistent with competition between glucose and 3‐methylglucose for the glucose transfer system at cell surfaces.5. The similarity between the effects upon cerebral metabolism of hypoglycaemia and the interference by a non‐metabolizable sugar with glucose transport into the brain, is discussed.