Corrosion of steel reinforcement is one of the main causes of damage in concrete structures. Often the corrosion of reinforcement steel is influenced by cracks in the concrete. Cracks in concrete structures are often produced due to loads, shrinkage or thermal gradients. Once a crack is formed, it disrupts the spatial continuity of concrete and leads to the corrosion of steel by the macro-cell mechanism. The steel at the crack undergoes localized corrosion, while the steel away from the crack remains passive. This paper presents the results of an experimental program which aims to investigate the response of steel, embedded inside cracked concrete and with an established macrocell, to external polarization. The results of linear polarization, performed on cracked concrete specimens containing a segmental steel bar with external electrical connections, are presented. A simple circuit-based model, which allows for predicting the polarization response of the macro-cell is presented. The results of the model indicate that there a spatial variation in the applied current relative to the crack. It is shown that the applied current primarily flows through the active steel located near the crack. © 2006 by NACE International.