Twenty-six patients with gliomas of WHO-grades two to four were examined with dynamic positron emission tomography (PET) and 18F-2-fluoro-2-deoxy-D-glucose (FDG). FDG rate constants and derived glucose metabolic rates (MRdyn) were determined in solid tumor tissue and in tumor-free brain tissue. In addition, glucose metabolism was also calculated from single scans recorded 30 to 40 min after injection (MRstat). All three rate constants, K1, k2, and k3, were significantly correlated with MRdyn in tumor-free brain. In contrast, in gliomas only k3 was significantly correlated with MRdyn. The ratio of k3 in tumors to k3 in tumor-free brain was also significantly related to histological tumor grade. The results indicate that FDG uptake in brain tumors is governed by FDG phosphorylation and is rather independent from the variation of FDG transport. A comparison between glucose metabolic rates calculated by an autoradiographic approach (MRstat) with the calculation based on individually fitted rate constants (MRdyn) revealed a very close correlation in spite of a moderate systematic difference in absolute values.