Sequential positron emission tomographic scans with [18F]-2-fluorodeoxyglucose (PET-FDG) were performed on 14 patients with malignant gliomas. All patients had prior brain irradiation. Five patients received adjuvant eight-drugs-in-one-day chemotherapy (experimental subjects) and 9 did not (control subjects). Ratios between the maximal tumor regional cerebral metabolic rate for glucose (rCMRGlu) and the contralateral white matter rCMRGlu, the glucose uptake ratio, were determined. Percent changes in the ratio 1 day after chemotherapy in experimental subjects, and 30 days after the baseline scan in controls, were of prognostic significance. In both groups, patients with the largest percent changes in rCMRGlu had the shortest survival. In contrast, the baseline glucose uptake ratio did not predict length of survival.