Numerous inclusions were diffusely observed in the neurons and glial cells in the cerebral cortex of a patient with progressive dementia. These inclusions were initially produced by rough ER in the cells and gradually enlarged destroying the rough ER membranes. The nature of these inclusions was neutral mucopolysaccaride including protein histochemically. In the nuclei of the nerve cells and glial cells, some types of intranuclear virus-like inclusions were found. The first type was papova virus-like structure with high electron density measured 30--35 nm in diameter. The second type was paramyxovirus-like structure with granulo-fibrilar shape. The third type was large hexogonal core with high electron density measured 100 nm in diameter. These intranuclear virus-like bodies were not specific in the present case; however, it was speculated that intranuclear virus-like inclusions might have a deep relation to change the function of the nuclei and produced large intraplasmic inclusion bodies.