Several cyclic GPIIb/IIIa receptor antagonists were labeled with 99mTc by the preformed chelate approach using chelators such as H4L1 [4,5-bis(mercaptoacetamido)pentanoic acid], H4L2 [3,4-bis-(mercaptoacetamido)benzoic acid], H3L3 [2-(mercapto)ethylaminoacetyl-L-cysteine], H4L4 [N-(mercaptoacetyl)glycylglycylglycine], H4L5 [N-[2-(mercapto)propionyl]glycylglycylglycine], and H4L6 [N-[2-(mercapto)propionyl]glycylglycyl-gamma-aminobutyric acid]. In this approach, the [99mTc]chelator complexes are formed first, followed by the activation of the carboxylic group on the complex by formation of its tetrafluorophenol (TFP) ester and the conjugation of the TFP ester with an amino group of a cyclic GPIIb/IIIa receptor antagonist. The 99mTc-labeled cyclic GPIIb/IIIa receptor antagonists were characterized by radio-HPLC (high-performance liquid chromatography); differences in lipophilicity of the [99mTc]chelator-peptide conjugate are attributable to the effects of both the cyclic peptide and the chelator.