The correlation between cerebral glucose utilization and brain surface potassium concentration (BS-K+) was studied during reperfusion following bilateral cerebral ischemia in the gerbil. Cerebral glucose utilization rate was measured by the 14C-2-deoxyglucose method and BS-K+ was continuously monitored by a potassium sensitive membrane electrode. BS-K+ increased from 3.0 +/- 0.6 mM (mean +/- S.D.) before ischemia to 58.7 +/- 17.3 mM 30 minutes after the occlusion of both common carotid arteries. The rate of decline of BS-K+ after release of occlusion differed between animals. Glucose utilization rate in the cerebral cortex immediately under the potassium electrode was low but homogeneous in 7 animals while in 5 animals the metabolic pattern was heterogeneous with areas of both low and high glucose metabolism. The former animals exhibited a fast recovery of potassium flux while the latter animals showed a slow recovery. Glucose utilization rate and potassium half recovery time were linearly correlated. These studies suggest that the reason that potassium flux may not recover rapidly in postischemic brain tissue is due to the lack of sufficient energy for a rapid re-establishment of the ion gradient across the cell due to the inefficient energy production of anaerobic glycolysis.