The heavy use of 9 9 m Tc in nuclear medicine and the recent development of 1 8 8 Re radiopharmaceuticals have encouraged the comparative study of Tc and Re coordination compounds. In this work, the electrochemistry of [M v O 2 (amine) 2 ] + (M = Tc,Re; amine = ethylenediamine, 1,3-diaminopropane, diethylenetriamine, triethylenetetramine) complexes is studied by cyclic voltammetry and the results are compared. The voltammograms and the results are compared. The voltammograms of these compounds, obtained at different pH values, show that [ReO 2 (amine) 2 ] + cations are thermodynamically stable even when protonated. On the other hand, analogous Tc compounds are not so stable and easily decompose if existing as [Tco(OH) (amine) 2 ] 2 + .