The concentration of extracellular potassium, [K+]e, was measured in parietal cortex and basal ganglia of rats during and after ten minutes of complete cerebral ischemia. The post-ischemic normalization of [K+]e was considerably delayed in parietal cortex compared to basal ganglia, but in both regions, [K+]e reached its normal concentration within 4 min of the end of the ischemia. Also, in both regions blood flow was elevated at the time of maximal [K+]e decrease. Our findings suggest that the normalization of [K+]e and cerebrovascular resistance after ischemia are related by positive feed-back, possibly via the stimulation of Na+-K+-ATPase.