OUTLINE: Patients are stratified by histologic type (anaplastic astrocytoma and glioblastoma multiforme vs brain stem glioma vs medulloblastoma and primitive neuroectodermal tumors vs ependymoma vs low grade glioma vs others). Patients receive phenylacetate as a continuous intravenous infusion on days 1-28. Courses of treatment are given continuously without rest. Treatment continues in the absence of disease progression or unacceptable toxicity. Patients are followed weekly.