While there are a number of reports dealing with the effect of irradiation on patients with tumor of the brain, few studies of the histologic changes so produced have been made. Alpers and Pancoast1studied a series of twenty-two cases of glioma in which specimens were available before and after treatment. Like Bailey,2they found medulloblastoma to be sensitive to roentgen rays. Alpers and Pancoast reported changes in ependymoma following roentgen irradiation (increase in connective tissue stroma, thickening of the blood vessels and increase in necrosis). No appreciable change was observed in oligodendroglioma, astrocytoma or glioblastoma. Brody and German3concluded that fibrosis follows roentgenotherapy in cases of medulloblastoma. Deery4reported a study of fifty cases of glioma in which preirradiation and postirradiation specimens were available. Some of the tumors of each of the three types (medulloblastoma, glioblastoma and astrocytoma), constituting most of the series, showed "striking