Forty-one to 104 evaluable patients with temozolomide-resistant anaplastic glioma will be enrolled in this study. Total accrual on this study will not exceed 116 patients. The patients will receive daily temozolomide on 5 consecutive days (days 1-5) along with bolus infusions of O6-BG on days 1, 3, and 5 and a continuous infusion of O6-BG beginning immediately after the first bolus infusion and continuing until immediately prior to the last bolus injection. Patients will be evaluated for AEs during the course of therapy. Patients may receive treatment at the same dose level until appearance of significant treatment-related toxicities, disease progression or withdrawal of consent.