There is no standard treatment for patients with recurrent gliomas, and their prognosis remains poor. 2-Chlorodeoxyadenosine is a purine analogue that has significant activity in many low-grade lymphoproliferative disorders. The authors conducted a phase II study to determine the efficacy of 2-chlorodeoxyadenosine in patients with recurrent gliomas. Patients with a histologically confirmed primary brain tumor with evidence of progression after radiation therapy were eligible. Protocol treatment consisted of 2-chlorodeoxyadenosine 7.0 mg/m2 intravenously on days 1 through 5 every 28 days. For those with a history of prior nitrosourea therapy, the dose of 2-chlorodeoxyadenosine was reduced to 5.6 mg/m2 on days 1 through 5. Treatment was continued until progression or a maximum of 12 cycles. Fifteen patients with recurrent astrocytomas or oligoastrocytomas of all grades were entered in the study. Treatment was well tolerated. Major toxicities were myelosuppression and neurotoxicity. No responses were seen. The authors conclude that although 2-chlorodeoxyadenosine is well tolerated, no demonstrable activity in patients with recurrent gliomas was established.