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Purpose: Glucagon-like peptide-1 receptor (GLP-1R) is a molecular target for imaging of pancreatic beta cells. We compared the ability of [Nle,Lys(Ahx-NODAGA-Cu)NH]-exendin-4 ([Cu]NODAGA-exendin-4) and [Nle,Lys(Ahx-NODAGA-Ga)NH]-exendin-4 ([Ga]NODAGA-exendin-4) to detect native pancreatic islets in rodents. Procedures: The stability, lipophilicity and affinity of the radiotracers to the GLP-1R were determined in vitro. The biodistribution of the tracers was assessed using autoradiography, ex vivo biodistribution and PET imaging. Estimates for human radiation dosimetry were calculated. Results: We found GLP-1R-specific labelling of pancreatic islets. However, the pancreas could not be visualised in PET images. The highest uptake of the tracers was observed in the kidneys. Effective dose estimates for [Cu]NODAGA-exendin-4 and [Ga]NODAGA-exendin-4 were 0.144 and 0.012 mSv/MBq, respectively. Conclusion: [Cu]NODAGA-exendin-4 might be more effective for labelling islets than [Ga]NODAGA-exendin-4. This is probably due to the lower specific radioactivity of [Ga]NODAGA-exendin-4 compared to [Cu]NODAGA-exendin-4. The radiation dose in the kidneys may limit the use of [Cu]NODAGA-exendin-4 as a clinical tracer. [ABSTRACT FROM AUTHOR]