The glucose metabolism of the retina was studied in vivo, by determining glucose, oxygen and lactate a-v differences for choroidal and retinal blood in pigs at different levels of intraocular pressure. At normal intraocular pressure the choroidal a-v differences were 0.07 and 0.11 mmol/l for glucose and oxygen respectively. The corresponding figures for the retina were 0.44 and 2.15. At increased levels of intraocular pressure the choroidal and retinal glucose and choroidal oxygen a-v differences increased, thus at least partly compensating for reduced blood flow. A major part of the oxygen and glucose consumed by the retina was delivered by the choroid. The total amount of oxygen extracted from choroidal and retinal blood could only account for complete oxidation of 37% of the extracted glucose. The results obtained in determinations of lactate a-v differences indicate that part of the remaining glucose is used for anaerobic glycolysis.