The glucose and glycogen content of the vitreous body and retina of rabbits’ eyes were estimated in pressure ischaemia and insulin hypoglycaemia. During 1 h of ‘pressure ischaemia’ two thirds of the substrate required for maintaining anaerobic glycolysis was supplied from the vitreous body. It was demonstrated by a model experiment that the energy reserves of the vitreous body were consumed by the retina exclusively. One of the factors limiting the recovery time of the retina is the decline of anaerobic glycolysis and not the exhaustion of the glucose reserve. A possible correlation with the recovery time of the ERG is discussed. There is no relation between the replenishment of the carbohydrate reserve and the normalisation of the ERG.