1. Changes in brain and hind-limb blood flow and metabolism have been studied in six dogs before and after the acute shunting of portal vein blood into the systemic circulation.
2. An initial increase in brain blood flow, oxygen and glucose consumption was found.
3. More prolonged shunting caused a fall in flow and in oxygen and glucose utilization by the brain.
4. Although peripheral blood flow and oxygen consumption were reduced by shunting glucose consumption was increased throughout the period of shunting.
5. The possible mechanisms of these changes is discussed, together with their relevance to the causation of encephalopathy in patients after portacaval shunts.