To determine whether barbiturate administration can improve oxygenation, oxygen availability (aO2) and local cortical blood flow (ICBF) were measured in cats before and during middle cerebral artery occlusion (MCAO) using 10 platinum electrodes distributed over the cortex. Halothane/N2O anesthesia was used during the surgical preparation and N2O with a relaxant thereafter. After 15 to 30 min of MCAO, 50 mg/kg of pentobarbital was infused slowly. Measured from electrodes in severely ischemic cortex, aO2 increased if the blood pressure was maintained with dopamine. Control animals in which no pentobarbital was given showed no change in aO2 over the same period of time. In areas of cortex not affected by middle cerebral artery occlusion the aO2 did not change from control values despite a decrease in blood flow from 72.7 +/- 49.8 to 48.9 +/- 26.7 ml/min/100 g. Thus, pentobarbital appears to decrease ICBF and metabolism proportionally in well perfused cortex so that aO2 remains constant, while improving the flow to metabolism ratio in poorly perfused cortex so that aO2 rises.