Malignant oligodendrogliomas have been shown to be responsive to chemotherapy. The authors administered systemic chemotherapy to seven patients with oligodendroglioma or anaplastic oligodendroglioma, and to 14 with mixed oligodendroglioma-astrocytoma. Fourteen patients underwent chemotherapy before and seven after irradiation. The PCV (procarbazine, methyl-1-(2-chloroethyl)-1-nitrosourea (CCNU), and vincristine) chemotherapy was administered every 6 weeks (42-day cycles) for two to five cycles as follows: CCNU, 110 mg/sq m on Day 1; procarbazine, 60 mg/sq m/day on Days 8 to 21; and vincristine, 1.4 mg/sq m/day on Days 8 and 29. Complete or partial (greater than 50% reduction in tumor mass) responses at 20 to 100+ weeks after treatment were noted in 11 (79%) of the 14 patients treated before irradiation, including two with anaplastic oligodendroglioma and nine with mixed tumors. Complete responses were seen in two patients, one with anaplastic oligodendroglioma and one with a mixed tumor. Partial responses were seen in three of seven patients treated after radiotherapy. Stabilization of tumor growth followed PCV chemotherapy in four patients (two treated before and two after radiotherapy). Tumor growth progressed in two patients during therapy despite an initial response and in two patients despite therapy. The authors conclude that mixed oligodendroglial tumors as well as anaplastic oligodendrogliomas are responsive to PCV chemotherapy.