Intracarotid injection of 50 to 100 mg of 5 to 10 % sodium amobarbital was given to 30 cases of epileptics, and change of the abnormal EEG was followed. 1) Unilateral focal cortical epileptogenic spikes were abolished by the ipsilateral administration, but not by the contralateral. 2) Amongst the cases of bilaterally synchronous spike and wave complex, two types of marked responses were obtained at the administration. One group manifested an abolishment of the complex from all leads of both hemispheres by administration on one side, but a transient inhibition of the spike component from the ipsilateral hemisphere by administration on the other side. This appears to indicate the complex originates from unilateral cortical focus which is located at the first side. This group may correspond with the secondary bilateral synchrony. 3) Another group manifested a transient inhibition of the spike component from ipsilateral hemisphere without abolishment of the complex at either side of administration. This may correspond with the primary bilateral synchrony, the so-called "ceutrencephalic origin". 4) No activation of characteristic abnormal activities in epileptics was found at the intracarotid injection of sodium amobarbital.