A molecular probe for use in imaging of pancreatic islets is provided. The molecular probe comprises a polypeptide represented by the following formula (1), (2), or (3), or a polypeptide having homology with the foregoing polypeptide,Z-HGEGTFTSDLSXQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH2 (1) (SEQ ID NO. 1)Z-HGEGTFTSDLSKQMEEEAVRLFIEWLXNGGPSSGAPPPS-NH2 (2) (SEQ ID NO. 2)B-HGEGTFTSDLSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH2 (3) (SEQ ID NO. 3)where, in formulae (1) and (2), "X" represents a lysine residue, the amino group of the side chain of the lysine residue being labeled with a radioactive nuclide, and "Z-" indicates that the α-amino group at the N-terminus is not modified, or is modified with a modifying group having no electric charge in formula (3), "B-" indicates that the α-amino group at the N-terminus is labeled with a radioactive nuclide and in formulae (1), (2), and (3), "-NH2" indicates that the carboxyl group at the C-terminus is amidated.
