The author had studied the action of some narcotics (urethane, chloralhydrate, barbital, luminal-Na, sulfonal, morphine hydrochl., ether and chloroform) on choline esterase and the influence of these on acetylcholine content in the central nervous system and the result is as follows: 1) These drugs inhibited the action of choline esterase. 2) The intensity of the action of these drugs (except ether and chroloform) on esterase had following order, i.e. morphine>barbital>chloralhydrate>sulfonal> urethaue>luminal. Except of sodium salt of luminal the action of those drugs is approximately proportional to their molecular weight. 3) The relation of the inhibitory action between these drugs (added luminal, brovarin) and choline esterase is linear. 4) The acetylcholine content in the central nervous system of the mouse was increased by these drugs.