Disturbances of the cerebral blood flow were induced by compressing the tube connected to the carotid arteries or depressing the perfusion pressure by a modification of the cat brain perfusion method devised by Geiger et al. In these experiments the amount of cerebral blood flow was rapidly and drastically decreased and then restored to normal flow rate, and changes taking place in EEG during these experiments were studied. The results are briefly sum-marized as follows. 1. When the cerebral blood flow is rapidly and drastically decreased, within several to 10 odd seconds EEG turns to low voltage, then high voltage slow activities appear followed by flattening. When the cerebral blood flow is restored there appear bursts of high voltage slow activities at first, then fast activities gradually make their appearance, but the high voltage slow activities gradually diminish, finally returning to the original EEG These changes coincide well with those changes in EEG clinically observable as in the case of circulatory disturbance of the brain. 2. Aspects of the EEG changes differ according to the rate of decrease in the cerebral blood flow, and in the decrease of about 20-24% cerebral blood flow, EEG shows apparently no appreciable changes, but the frequency autoanalyzer reveales a slight decrease in the fast activities and an increase of slow activities. 3. In the instance where the cerebral blood flow is decreased 21-35%, EEG increases high voltage slow activities. 4. Where the cerebral blood flow decrease amounts to over 37% or it has transiently ceased, EEG takes the foregoing course and then is flattened. 5. Under the diminished conditions of cerebral blood flow, the decrease in the fast activities and the increase in the slow activities are found. The faster the EEG activity, the greater is its decrease, and the slower the EEG activity, the greater is its increase. 6. At the recovery stage of the cerebral blood flow, the rate of increase in the faster activities is high and slow activities are diminished 7. At the time when the cerebral blood flow is decreasing and also at the recovery stage when there appear high voltage slow activities, some of EEG's take the pattern of spike and wave complex.