DISEASE CHARACTERISTICS: Histologically proven oligodendroglioma or oligoastrocytoma with at least 25% oligodendroglial elements Recurrent or progressive disease following radiotherapy At least 3 months since prior radiotherapy Measurable disease by MRI or CT scan Lesion must have a diameter of at least 1 cm No progressive neurological deficits from the present recurrence No new neurological deficits interfering with daily activities No tumor causing midline shift or brain stem compression due to which a rapid deterioration is to be expected in case of no response No signs of increased intracranial pressure No extracranial disease