Ten per cent metrazol solution was experimentally injected in cats and the changes of choline-esterase (ChE) at the maximum stage of convulsion was histochemically investigated by Koelle modification. 1) The ChE of nerve cells mostly increased in normal cases relatively in peripheral part of protoplasma, while in convulsion cases it was considered to be even in central part of protoplasma. 2) ChE is increased in each area of the caudate nucleus by convulsion. 3) The increase is especially remarkable in the large cells of the caudate nucleus. 4) The dorsolateral side of the caudate nucleus (Cd., Cm.) has more increase of ChE than the ventromedial side by convulsion, and Cm. has the most increase, then in the order of Cd., Cl. and Cv. to the least. 5) In cases without convulsion, there is no difference of ChE distribution among these areas, and even the large cells have no marked increase of ChE.