1 The accumulation of glucose in the brain produced by the administration of phosphatidylserine liposomes into mice has been studied by measurement of the cerebral contents of glycolytic intermediates and high-energy compounds. 2 With a normal supply of oxygen to the brain, inhibition of glycolysis is indicated mainly at the phosphofructokinase step. The ratio of glucose-6-phosphate to fructose-1,6-diphosphate increased, whereas the levels of pyruvate and especially lactate decreased. 3 Under conditions of cerebral ischaemia, the administration of phosphatidylserine delays glycogen mobilization and ATP use. As a consequence of decreased energy utilization, the brain adenylate energy charge remains at a high level. 4 It is concluded that the phosphatidylserine-induced glucose accumulation in the brain is due to reduced energy expenditure and therefore to a decrease in carbohydrate consumption. The inhibition of glycolysis by the high level of adenylate energy charge is probably the control mechanism explaining the decreased carbohydrate utilization.