We tested clinical significance of hemocirculatory and metabolic values and ratios as determined by positron emission tomography (PET) in twenty-three patients with cerebral gliomas. Regional cerebral blood flow (rCBF), blood volume (rCBV), oxygen extraction fraction (rOEF), and metabolic rates of oxygen (rCMRO2) and glucose (rCMRGl) were measured prior to treatment using PET with 15O2, C15O, 15O2, and 18F-fluorodeoxyglucose tracers. For the quantitative analysis, regions of interest were delineated on tumor regions including peak activity, the contralateral gray and white matter. The regional values and the ratios of tumor/gray matter and tumor/white matter were compared to performance status (PS) according to the five functional grades system which are defined by the Japan Society for Cancer Therapy, tumor progression-free time (PFT), survival time (ST) from the time of the PET study, regardless of type of therapy. As with rCMRGl, the tumor values and the ratios of tumor/gray matter and tumor/white matter correlated significantly with PS (tumor/gray: p less than 0.05, tumor/white: p less than 0.01). Both the gray rCBF and the tumor/gray rCBF ratio had close relation with PS and/or PFT (p less than 0.05). The gray matter rCMRO2 and the tumor/gray matter rCMRO2 ratio related significantly (gray matter: p less than 0.01, tumor/gray: p less than 0.05) to each clinical parameter of PS, PFT, and ST. These indicate that values and ratios as determined by PET can be useful in predicting the prognosis of glioma patients.