In this work, the electron transfer reactions of horse spleen ferritin at tin-doped indium oxide electrodes were investigated for the first time. Cyclic voltammetry reveals that ferritin adsorbs from phosphate solution into a layer composed of two adsorbed states, the relative packing density of the states depending strongly on ionic strength. Upon reduction, the initial layer reconstructs into a new one with faster electron-transfer kinetics. Reduction of the adsorbed layer in the presence of ethylenediaminetetraacetic acid results in the disappearance of any further voltammetric response indicating that transport of iron from the protein shell had been induced electrochemically.