Parabiosis was performed between an ep-mouse, having had convulsive seizures, and a CF(1)-mouse, one of normal other species, and biochemical changes in the brain induced by this procedure were investigated. The results of this experiment were as follows: 1. Water content in the brain of the ep-mouse was larger than in the one of the CF(1). It was decreased 6 days after the procedure to the level between the contents in the ep-and the CF(1)-mice of preparabiosis period. At the 12 th postparabiosis day, both contents were decreased to regain the preparabiosis level of the CF(1). The variation in the course was due to the change of the free water content but not due to the bound water content. 2. Total sodium content in the ep-mouse was remarkably large in contrast to the one in the CF(1)-mouse. It was gradually decreased to the level of the CF(1) at the 12 th postparabiosis day. 3. Total potassium content in the ep-mouse was also markedly large in contrast to the one in the CF(1)-mouse, and it followed the tendency of the variation as sodium content.