The anodic dissolution behavior of three samples of magnesium anodes, with different electrochemical efficiency, was studied in two test aqueous solutions: 3% NaCl and saturated CaSO4-2H(2)O-Mg(OH)(2). Polarization curves and electrochemical impedance spectroscopy (EIS) were used. It was found that activation processes takes place at the metal-electrolyte interface. These processes can be represented by two parallel electric equivalent circuits, arranged in series, and in series with the resistance of the solution. It is proposed that the physical meaning of the two parallel circuits can be associated to a charge transfer process and to the presence of a layer of corrosion products on the surface of the metal. (c) 2005 Elsevier Ltd. All rights reserved.