INTRODUCTION: In this study, we assessed the whole-body biodistribution and radiation dosimetry of the new glutamatergic ligand (11)C-ABP688. This ligand binds specifically to the metabotropic glutamatergic receptor of subtype 5 (mGluR5). MATERIALS AND METHODS: The study included five healthy male volunteers aged 20-29 years. After intravenous injection of 240-260 MBq, a series of four to ten whole-body positron emission tomography/computed tomography scans were initiated, yielding 60-80 min of data. Residence times were then calculated in the relevant organs, and the software packages Mirdose and Olinda were used to calculate the absorbed radiation dose and the effective dose equivalent. RESULTS: Of the excreted (11)C activity at 1 hour, approximately 80% were eliminated via the hepato-biliary pathway and 20% through the urinary tract. The absorbed dose (mGy/MBq) was highest in the liver (1.64 E (-2) +/- 5.08 E (-3)), gallbladder (8.13 E (-3) +/- 5.6 E (-3)), and kidneys (7.27 E (-3) +/- 2.79 E (-3)). The effective dose equivalent was 3.68 +/- 0.84 microSv/MBq. Brain uptake in the areas with high mGluR5 density was 2-3 (SUV). The agreement between the values obtained from Mirdose and the Olinda was excellent. CONCLUSION: (11)C-ABP688 is a very promising ligand for the investigation of mGluR5 receptors in humans. Brain uptake is high and the effective dose equivalent so low that serial examinations in the same subject seem feasible.