Background and Objective: Radiotracer diagnosis of insulinoma, can be done using somatostatin or glucagon-like peptide 1 (GLP-1). Performance of GLP-1 antagonists tends to be better than of agonists. Methods: We investigated the uptake of the antagonist exendin (9-39), radiolabeled with technetium-99m. Two different sites of the biomolecule were selected for chelator attachment. Results: HYNIC-beta Ala chelator attached to serine (C-terminus) of exendin, was associated with higher tumor uptake than to aspartate (N-terminus). Conclusion: The chelator position in the biomolecule influenced receptor uptake.