Glutamic acid, γ-aminobutyric acid and glial fibrillary accidic protenin positive cells in the hippocampus of E1 mice and ddY mice were examined immunohistochemically. The shape of glutamic acid positive cells in CA1, CA2, CA3 and CA4 of hippocampus were expanded compar-ed to that of ddY mice. There was a space between cells and cells containing glutamic acid and the nucleus of such cells was larger in the CA1 of E1 mice than that of ddY mice. The glutamic acid cells were irregular and the nucleus was larger in the gyrus dentantus of E1 mice than that of ddY mice. There was an intermittence in the process of glutamic acid cells in the area of of str. radiatum of E1 mice. γ-Aminobutyric acid-posititve cells seemed to be expanded in CA1 of CA2, CA3, and CA4 and gyrus dentatus and there was space between such cells in the CA1 of E1 mice. Large γ-aminobutyric acid positive cells, which were located close to the gyrus dentatus in ddY mice, were not found in E1 mice. The number of γ-aminobutyric acid-positive cells was lower in E1 mice than in ddY mice. A greater number of glial fibrillary acidic protein postive cells was found in the area of the hippocampus in E1 mice than in ddY mice. These results suggest that E1 mice are genetically epileptic mice.