In order to study the viral etiology of human brain tumors, attempts were made to isolate cytopathogenic agents from human brain tumors by the tissue culture of tumor tissues and by the mixed culture of tumor tissues with HeLa cells. Five glioblastomas, a mixed form of glioblastoma and fibrosarcoma, two astrocytomas, two ependymomas, two meningiomas, an oligodendroglioma, a spongioblastoma pola...