Vascular glioblastomas become liquefied when contaminated with spores of the non-pathogenic Clostridium butyricum M 55. The spores are administered by intracarotid injection. The oncolysis is complete one week after injection. The glioblastoma is converted into a brain abscess which is then operated on appropriately. Forty nine patients have been treated in this manner. The rate of recurrence, however, remained uninfluenced.