Noninvasive beta cell mass (BCM) quantification is a crucial tool to understand diabetes development and progression. [(111)In]exendin is a promising agent for in vivo beta cell imaging, but tracer testing has been hampered by the lack of well-defined rodent models.Biodistribution and pancreatic uptake of [(111)In]exendin were compared in rats and mice. In selected models, the amount of [(111)In]exendin accumulation in the pancreas and other organs was determined using a model of alloxan-induced beta cell loss. GLP-1R expression levels were analyzed by RT-PCR and immunohistochemistry.Namely Brown Norway rats showed beta-cell-specific tracer accumulation and favorable pancreas-to-background ratios for noninvasive BCM determination. Mice displayed receptor-mediated [(111)In]exendin uptake in endocrine and exocrine pancreas, in spite of very low GLP-1R expression in exocrine tissue.Rats display better characteristics for in vivo BCM determination than mice and are suggested as a more adequate model for humans.