Abstract: Provided herein are compounds useful for diagnostic imaging and/or therapeutic purposes. Each compound comprises a ligand for the chemokine receptor CXCR4, which has a binding affinity for the CXCR4 receptor, measured as IC50 in the presence of 125I-CPCR4, of 250 nM or lower. The ligand is a cyclic oligopeptide moiety having a motif B-Arg or B-(Me)Arg within the cyclic moiety, wherein B is a basic amino acid, a derivative thereof, or phenylalanine, provided that the motif is B-Arg when B is a N?-methyl derivative of a basic amino acid, and provided that the cyclic oligopeptide moiety has a sequence other than cyclo[D-Tyr-Arg-Arg-NaI-Gly] or cyclo[D-Tyr-Orn-Arg-NaI-Gly].