RESUMEN
Xixin [Asarum heterotropoides Fr. Schmidt Var mandshuricum ( Maxim ) kitag] is a Chinese drug which has a little toxicityas recorded in ancient Chinese medical books. It was demon-strated in this article that the toxicity of Xixin was caused by itsessential oil. When the mice were administered with Xixin oil and its decoction without oil in equal doses separately, the mortality rate for the oil group was 70%, whereas no death was observed in the group of decoction without oil. By synchronous recording the EKG and EEG of cerebral cortex, hippocampus and reticular formation of midbrain in the rabbits, it was revealed that the EKG underwent following changes after the administration of Xixin oil: fast wave of low amplitude→slow wave of high amplitude→slow wave of low amplit ude→burst-suppression pattern→electrical silence. EEG vanished after the electrical silence of cerebral cortex,hippocampus and midbrain reticular formation.The LD50 and ED50 of Xixin oil was calculated 27.0?0.4ml/kg and 18.3?0.8ml/kg respectively,safety coefficient 1.47, being significantly less than control drug sodium amytal.