--Disease Characteristics-- Histologically proven refractory or recurrent brain neoplasms Glioblastoma multiforme Anaplastic astrocytoma Gliosarcoma Anaplastic oligodendroglioma Mixed anaplastic glioma Unequivocally progressive primary brainstem tumors following primary therapy Measurable disease --Prior/Concurrent Therapy-- Biologic therapy: Not specified Chemotherapy: At least 4 weeks since prior chemotherapy At least 6 weeks since prior nitrosoureas or mitomycin Endocrine therapy: Not specified Radiotherapy: Prior radiotherapy allowed Surgery: Prior surgery allowed --Patient Characteristics-- Age: Not specified Performance status: ECOG 0-2 Karnofsky 60-100% Hematopoietic: Granulocyte count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 2.0 mg/dL SGOT no greater than 4 times normal Renal: Creatinine no greater than 2.0 mg/dL Pulmonary: FEV1 greater than 1 L if symptomatic pulmonary disease present Other: No other concurrent malignancies Not pregnant or lactating Negative pregnancy test Fertile patients must use effective contraception