An attempt was made to analyze the changes of EEG secondary to the intracarotid injection of 50 to 100 mg of sodium amobarbital: 33 trials on 20 patients. 1) There appeared to be a marked change in all cases; limited or dominant ipsilaterally to the side of administration. 2) The latter was found in 22 out of 33 trials, and noted at the records of the frontal leads. 3) The change was composed of high amplitude and low frequency or of low amplitude and high frequency or of the mixed of both, occurring at 3 to 6 seconds after the onset of the injection and gradually disappearing to regain the normal state within 30 minutes. 4) These changes, especially the high amplitude and slow waves immediately after the injection at the same side were markedly noticed when the injection was in large dosage and in high speed. 5) There was no difference in such changes given arise by either side of administration in the same patient. 6) It is to be noted that there were no hazardous complications at the intracarotid injection of 10 % sodium amobarbital under sufficient attention.