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Resumen del autor: With the increasing growth of several areas in the modern society, become raising the necessity to generate and carry electrical energy to the great downtons. Because of that it was necessary to heigten the generation and transport of electrical energy to the big towns. To carry the energy we usally use power towers with steel structure foundation with zinc coating protection (galvanic coating). This foundation is undergrounded on the soil and because of that it may cause a high rate of corrosion, usually detected by a conventional potential measurement, utilizing a CuSO4 reference electrode. It is belivied that corrosion resulted from the action of stray currents that flow throught the ground to close the loop between neigboring towers. Stray currents originate in the lightning rod cables of the power line towers, induced by the strong eletromagnetic and electric fields of the energized power lines. The intensity and direction of those currents were measured, indicating substantial values of both AC and DC components. The potential of the tower ground system, measured in the perpendicular direction of the main axis of the power line, was plotted as a function of the distance to the tower base. The results clearly indicated the propensity to corrosive attack in the anodic towers as reflected by the slope of the plot, whereas no signs of corrosion could be found in the reverse slope, confirming the visual inspection of the foundation. The profile of the potential plots could be changed providing the electric insulation of the lightning rod cable.