Parabiosis was performed between an ep-mouse, having had convulsive seizures, and a CF(1)-mouse, one of the normal other species, and biochemical changes as to cholinesterase activity and acetylcholine content in the brain induced by this procedure were investigated. The results of this experiment were as follows: 1. Cholinesterase activity was significantly low in the brain of the ep-mouse compared with the CF(1)-mouse. This difference was averaged by parabiosis formation, and both activities were decreased to the preparabiosis level of the ep-mouse at the 12 th postparabiosis day. 2. Total acetylcholine content was definitely large in the brain of the ep-mouse compared with the CF(1)-mouse, but it was rapidly recovered to the preparabiosis level of the CF(1)-mouse. In contrast to it, the content in the CF(1)-mouse remained unchanged throughout the postparabiosis period.