Regional cerebral blood flow, blood volume, fractional oxygen extraction, and oxygen consumption were measured by positron emission tomography in 4 stroke patients prior to and 6 months following omental transposition surgery. Preoperatively, 3 patients showed the typical picture of established infarction with a matched reduction in flow and oxygen metabolism and a normal oxygen extraction fraction in the symptomatic hemisphere. One patient showed a chronically impaired perfusion reserve with a proportionally greater reduction in flow than oxygen metabolism and a compensatory rise in oxygen extraction ratio. No change in the physiological parameters was demonstrated in the postoperative studies.