Patients receive O6-benzylguanine IV over 1 hour, then, 1 hour later, carmustine IV is administered over 1 hour. Treatment is repeated every 6 weeks for up to 1 year in the absence of disease progression or unacceptable toxicity. Cohorts of 3-6 patients each receive escalating doses of carmustine until the maximum tolerated dose (MTD) is reached. The MTD is defined as the dose level at which fewer than 2 of 6 patients experience dose limiting toxicity (DLT). If myelosuppression is the DLT, stratum 1 is closed and patients are accrued to stratum 2. If neutropenia is the DLT in stratum 2, patients receive filgrastim (G-CSF) subcutaneously beginning on day 2 and continuing until blood counts recover. Patients are followed every 6 months for 4 years, then annually thereafter.