Histologic diagnosis: Previously treated brain tumor patients with any histologic diagnosis who have recurrent or progressive disease after radiation or chemotherapy, including bone marrow transplant. For patients with brainstem tumors the requirement for histologic verification may be waived. However, for patients with brainstem tumors treated with hyperfractionated radiotherapy a biopsy, a PET scan or NMR spectroscopy is strongly recommended prior to study entry to rule out radionecrosis as a possible cause of MRI changes. A biopsy, PET scan, or NMR spectroscopy is required for patients treated with radiosurgery prior to study entry.