The effect of chemotherapy with procarbazine, CCNU, and vincristine in an anaplastic oligoastrocytoma was monitored by repeated positron emission tomography (PET) with C-11-methionine (C-11-MET). Chemotherapy caused a continuous decline of active tumor volume at a rate of approximately 2.4% per day, resulting in complete remission that persisted until the end of follow-up at 3 years. Thus, the authors conclude that C-11-MET PET may be useful for monitoring chemotherapy in gliomas and deserves further study.