OUTLINE: This is a dose escalation study of O6-benzylguanine (O6-BG). Patients in the first cohort receive O6-BG IV over 1 hour followed by continuous infusion of O6-BG for 2 days prior to surgery. Patients undergo surgical resection and receive up to 8 polifeprosan 20 with carmustine implants (Gliadel wafers) in the resected tumor cavity. Cohorts of 14 patients receive escalating doses of O6-BG until 11 out of 14 patients in a cohort have complete suppression of AGT levels. Once the dose of O6-BG that completely suppresses AGT has been established, subsequent patients receive O6-BG IV beginning at least 1 hour prior to surgery followed by the established continuous infusion dose beginning on the day of surgery. The infusion continues for up to 14 days postoperatively. Cohorts of 6-12 patients receive lengthened durations of continuous infusion O6-BG until the maximum tolerated dose (MTD) is determined or the length of the infusion reaches 14 days. The MTD is defined as the dose preceding that at which 3 of 6 or 5 of 12 patients experience dose limiting toxicities. Patients are followed at 3, 6, 9, and 12 months, and then until death.