OUTLINE: Patients are stratified according to prior nitrosourea administration (yes or no). (Prior nitrosoureas stratum closed) An initial cohort of 3 patients per stratum is treated with intravenous O6-benzylguanine followed approximately 1 hour later by intravenous carmustine every 6 weeks. Additional cohorts of 3-6 patients are treated with escalating doses of carmustine until dose limiting toxicity (DLT) is observed. The maximum tolerated dose is defined as the dose at which no more than 1 of 6 patients experiences DLT. Courses are repeated every 6 weeks in the absence of disease progression or unacceptable toxicity.