In this study, we present the synthesis and characterization of the octadentate bispidine ligand, H(2)bispox(2) and its complexes with medicinally useful radiometal nuclides (In-111(3+) and Lu-177(3+)), including their X-ray diffraction single crystal structures with the stable isotopes. (InCl3)-In-111 radiolabels the ligand quantitatively at ambient conditions ([L] = 10(-5) M, room temperature, pH 7 and 15 min) and the in vitro human serum stability assays demonstrated high stability of the [In-111(bispox(2))](+) complex over 5 days. Moreover, the beta(- )emitter Lu-177 radiolabels the ligand at 37 degrees C in 30 min (pH 8). These initial investigations reveal the potential of the octadentate bispidine ligand H(2)bispox(2) as a useful chelator for In-111 and Lu-177-based radiopharmaceuticals.