Pancreatic β-cell mass (BCM) is a major determinant of the quantity of insulin that can be secreted. BCM is markedly reduced in type 1 diabetes because of selective autoimmune destruction of β-cells. Accurate assessment of BCM in human diabetes is limited to autopsy studies, which usually suffer from inadequate clinical information; thus, the development of noninvasive means of BCM measurement could be important in intervention therapy. The goal of this study was to develop such noninvasive methods for measuring BCM featuring target-specific imaging probes and to investigate whether this technique is feasible, accurate, and predictive of BCM in normal and diabetic states. Using a β-cell–specific monoclonal antibody IC2, modified with a radioisotope chelator for nuclear imaging, we showed that highly specific binding and accumulation to β-cells occurs after intravenous administration of the probe, with virtually no binding to exocrine pancreas or stromal tissues. Furthermore, we observed a direct correlation between accumulation of the probe with BCM in diabetic and normal animals. Nuclear imaging of the animals that received an injection of the radioactive probe showed major difference in signal intensity between normal and diabetic pancreases. The results from this study set the route for further development of imaging probes for measuring BCM that would aid in diagnosis and treatment of diabetic patients in the clinic.