After studying disturbing actions of various alkylphosphates such as ethylparathion, methylparathion, EPN, TEPP, Pestox 3, malathon, diazinon and dipterex on cholinesterase of the brain, liver, spleen and muscles in mice, the author observed the reactivating effects on cholinesterase by administering PAM, PATD, PPATD, PPAPD, PAD, DAM, and MINA to these animals. The results are as follows. 1. In the organs of the animals administered with alkylphopshates in the amount about half LD(50), cholinesterase in various organs is decreased to 30-60 per eent of the normal level. It has been found that muscle cholinesterase is markedly disturbed in the ease of TEPP administration, while the disturbance of brain cholinesterase is markedly less in the administration of Pestox-3. 2. The brain cholinesterase disturbed by alkylphosphates can be brought back to a certain degree with administration of oxime cempounds. Especially in ethylparation poisening the effect is just as good as thaf of PAM, brining back almost to the normal level. 3. The recovery rate of the brain cholinesterase parallels most closely with the theapeutic effect, judging from the mortality rate. 4. The behavior of cholinesterase differs according to the combination of alltylphosphates and oixme compounds and to different organs, but with an exception of Pestex-3, cholinesterase recovers in some organ. Only in the case of DAM and MINA there can be observed no fluctutions at all exepting muscle cholinesterase. 5. The reactivating action of oximes on the vesceral cholinesterase is only transient. 6. PAD is less effective on alkylphospate poisonning than PAM, and the concurrent use of PAD with any one of quarternary oximes does not enhance the recovery of cholinesterase activity.