Tc-99m labeled derivatives of N-Me-Arg-Gly-Asp containing cyclic peptide GP IIb/IIIa receptor antagonists are potential radiopharmaceuticals for the diagnosis of thrombosis. The design and synthesis of these peptides are described. These compounds are incorporated in rapidly growing thrombi under both arterial and venous conditions in canine models. Thrombi are clearly visible in images acquired at 50 min.