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Abstract: Introduction: Two 7-fluoroimidazobenzodiazepines (AH114726 and GEH120348), analogs of flumazenil, were labeled with fluorine-18 and evaluated as alternative radioligands for in vivo imaging of the GABAA/benzodiazepine receptor by comparing them to [11C]flumazenil in rhesus monkey. Methods: Radiotracers were prepared from the corresponding nitro-precursors in an automated synthesis module, and primate imaging studies were conducted on a Concorde MicroPET P4 scanner. The brain was imaged for 60 (12×5min frames) or 90min (18×5min frames), and data was reconstructed using the 3D MAP algorithm. Specificity of [18F]AH114726 and [18F]GEH120348 was confirmed by displacement studies using unlabeled flumazenil. Results: [18F]GEH120348 and [18F]AH114726 were obtained in 13–24% yields (end of synthesis) with high chemical (>95%) and radiochemical (>99%) purities, and high specific activities (2061±985Ci/mmol). The in vivo pharmacokinetics of [18F]AH114726 and [18F]GEH120348 were determined in a non-human primate and directly compared with [11C]flumazenil. Both fluorine-18 radioligands showed time-dependent regional brain distributions that correlated with the distribution of [11C]flumazenil and the known concentrations of GABAA/benzodiazepine receptors in the monkey brain. [18F]AH114726 exhibited maximal brain uptake and tissue time-radioactivity curves that were most similar to [11C]flumazenil. In contrast, [18F]GEH120348 showed higher initial brain uptake but very different pharmacokinetics with continued accumulation of radioactivity into the cortical regions of high GABA/benzodiazepine receptor concentrations and very little clearance from the regions of low receptor densities. Rapid washout of both radiotracers occurred upon treatment with unlabeled flumazenil. Conclusion: The ease of the radiochemical synthesis, together with in vivo brain pharmacokinetics most similar to [11C]flumazenil, support that [18F]AH114726 is a suitable option for imaging the GABAA receptor. [Copyright &y& Elsevier]