DISEASE CHARACTERISTICS: Radiological diagnosis of probable high grade glioma, or biopsy proven high grade glioma, undergoing neurosurgery (biopsy or tumor resection) with interactive MRI guided control Must have an enhancing cerebral lesion No radiological diagnosis of metastases due to multiple lesions

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 50-100% while on steroids Life expectancy: Not specified Hematopoietic: WBC at least 3,000/mm3 Granulocyte count at least 1,500/mm3 Platelet count at least 100,000/mm3 Prothrombin time no greater than 1.5 times upper limit of normal (ULN) Active partial thromboplastin time no greater than 1.5 times ULN Hepatic: Bilirubin no greater than 2 mg/dL AST and ALT no greater than 2 times ULN Renal: Creatinine less than 1.5 mg/dL Cardiovascular: No severe cardiac disease Pulmonary: No severe pulmonary disease Other: No other significant life threatening disease No known glucose-6-phosphate dehydrogenase deficiency or porphyria No other active malignancy No intractable seizures Not pregnant or nursing Effective contraception required of all fertile patients

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: Not specified Endocrine therapy:

Concurrent steroids allowed Radiotherapy: Concurrent radiotherapy allowed Surgery: See Disease Characteristics Other: At least 48 hours since prior MRI scan with contrast No concurrent active agent or investigational drug No concurrent use of other study treatment Concurrent antiseizure medication allowed