Kappa opioid receptor (KOR) PET imaging remains attractive to understand the role of KOR in health and diseases, and to help the development of drugs especially for psychiatric disorders such as depression, anxiety and addiction. The potent and selective KOR antagonist RTI-97 labelled with carbon-11 was previously demonstrated to display specific KOR binding in mouse brain by ex vivo autoradiography studies. Herein, we evaluated [11C]RTI-97 in rat by in vitro autoradiography and by in vivo PET imaging. The radiosynthesis of [11C]RTI-97 was optimized to obtain high molar activities. Despite a low cer-ebral uptake, the overall results showed an heterogeneous repartition and specific KOR binding of [11C]RTI-97 in brain, and a high and specific accumulation of [11C]RTI-97 in pituitary in accordance with KOR expression.