The initial stage of status spongiosus in Ammon's horn of two brains with panencephalopathic type of Creutzfeldt-Jakob disease (PE-CJD) was examined electron microscopically. The results obtained in this examination were as follows: initial formation of large vacuoles or cavities seemed to be the result of distension within cell processes, mainly astrocytes, and these vacuoles and cavities might gradually form status spongiosus. A very important finding in the present study was that all kinds of glial cells showed degenerative changes. It is concluded that glial insufficiency might be one of the pathogenetic mechanisms effective in panencephalopathic Creutzfeldt-Jakob disease.