Metallopeptides with a sequence of a biologically active alpha-melanocyte stimulating hormone (.alpha.-MSH), gamma-melanocyte stimulating hormone (.gamma.-MSH), or bombesin sequence of length n residues, wherein a residue including a nitrogen atom and sulfur atom each available for complexation to a metal ion is inserted at any position from between the two and three position to the C-terminus side of the n position, or alternatively is substituted for the residue at any position from the three position to the n position, with a metal ion complexed thereto, with any proline (Pro) residue which is either of the two residues on the immediately adjacent N-terminus side of the inserted or substituent residue comprising a nitrogen atom and sulfur atom available for complexation to a metal ion is substituted with a homolog.