The decapeptide Arg-Gly-Asp-Ser-Cys-Arg-Gly-Asp-Ser-Tyr, which contains two Arg-Gly-Asp (RGD) moieties in its sequence, has been successfully labeled with radioactive rhenium (Re-188) yielding a single, stable oxorhenium complex. This complex is being evaluated for possible application in oncology as a target-specific radiotherapeutic agent, because its radioactive technetium-99m analogue has already been applied for the scintigraphic detection of malignant melanoma in humans. For structural characterization purposes, the complex of the decapeptide was synthesized at the macroscopic level using nonradioactive rhenium (Re-185/Re-187). NMR and mass spectral analysis of the nonradioactive oxorhenium complex revealed that the decapeptide coordinates to the oxorhenium core through the N-amide of Asp3, the N-amide of Ser4, and the N-amide and S-thiolate atoms of Cys5 to form a complex of the ReO[N3S] type.