Complete cerebral ischemia lasting 20 and 30 min was produced in dog brains. Before and after complete ischemia early and middle latency auditory evoked potentials were recorded simultaneously. In all cases of complete ischemia for 30 min amplitudes of evoked potentials were diminished during the reperfusion period of 8 to 12 hours. In some cases evoked potentials reappeared only temporarily. After complete ischemia of 20 min duration, the amplitude of evoked potentials varied within a wide range. They could reach nearly normal values.