Changes of the electrolyte in the motor area of the cerebral cortex were experimentally studied in dogs during convulsions which were caused by the intravenous injection of metrazol. The results were as follows: 1) Chloride content increases at the preconvulsive stadium and also at the acme and reaches to its maximum at the repeated convulsive stadium. At the postconvulsive stadium it decreases nearly to the normal, but still remains a little higher than the normal 2) Sodium content decreases at the preconvulsive stadium and recovers gradually to the normal as the time elapses. 3) Potassium content shows no distinguished change. 4) Calcium content reaches the highest at the preconvulsive stadium and then decreases gradually to the normal as the time elapses. 5) Magnesium content at the preconvulsive stadium is the same as the normal and increases rapidly at the acme and at the repeated convulsive stadium but finally decreases below the normal. 6) From these facts stated above, it is considered that the changes of the electrolyte in the cerebral tissue during the convulsion are caused by the secondary changes due to convulsion.