Ion transport out of and into the Nafion(R) coating on an electrode during the electrochemical processes was studied using an electrochemical quartz crystal microbalance (EQCM). After saturated loading of [Os(bpy)(3)](2+), the first cyclic voltammogram (CV) initiated from the lower limit showed an anodic peak around 0.85 V vs. AgAgCl which, according to a previous study by Anson’s group, corresponds to ejection of the [Os(bpy)(3)](3+) complex from the Nafion(R) coating. However, the frequency change-potential (Delta f-E) curve obtained by EQCM showed an increase in the mass on the first positive scan. These contradictory results can be explained by the movement of water molecules in a direction opposite to that of [Os(bpy)(3)](3+) complexes. After a number of successive cycles, a steady state voltammogram was obtained. In this case the mass change was attributed mainly to the movement of the hydrated electroinactive counter-cations of the supporting electrolyte. The hydration numbers for two of the supporting electrolyte cations are in good agreement with the published results.