OBJECTIVES: I. Determine the dose of O6-benzylguanine that completely suppresses AGT levels in patients with recurrent malignant glioma. II. Evaluate the safety and tolerance of increasing duration for up to 2 weeks of continuously infused O6-benzylguanine at a dose that will completely suppress tumor AGT activity combined with intracranially implanted polifeprosan 20 with carmustine implants (Gliadel wafers) in this patient population.