The available literature on various side-effects occurring at theadministration of Antabuse all deals mainly with the development of severe psychotic symptoms. as for the causes of such side-effect systemic poisoning or the cerebral organic disturbances accompaning it or the activation of dormant factor can be pointed out, but in the present investigation the auther studied mild side-effects that usually appear transiently; namely drowsiness, malaise loss of appetite, sweating, headache, fever, and oppressive feeling by means of electroencephalogram. In 37 cases given Antabuse severe psychotic symptoms appear in one case, and mild sideeffect in 15 cases. Of them abnormal encephalographic waves appeared in 12 cases. One case indicated the existence of organic damages, and two cases the organic damages reactivating dormant epileptic factor or inducing epilepsy. The electroencepharogram of epilepsy in the case not revealing severe clinical symptoms was also reactivated; and in 4 cases the electroencephalogram of epilepsy or abnormal wave close to it appeared. The electroencephalogram was not reactivated in two cases with organic damages. In the other two cases the so-called transitional wave appeared. From these, the fact that 7 out of 12 cases had organic damages or revealed abnormal waves suggesting the existence of such damages indicates that the toxicity of Antabuse is virulent and that during the intoxication it will generally inflict damages to the brain.