Corrosion of reinforcing steel in concrete structures is a major durability issue worldwide. For monitoring and diagnosis, non-destructive test methods have been developed. Polarization measurements have become a widely used method for corrosion rate monitoring of reinforced concrete both in the laboratory as well as on site. However, in case corrosion inhibitors have been implemented in the concrete, some questions remain concerning the applicability and the interpretation of the polarization measurements. The purpose of this paper is to examine the influence of corrosion inhibitors on the Stern-Geary constant. In this work experiments were performed on carbon steel in simulated concrete pore solutions with and without the presence of corrosion inhibitors. Results have shown that corrosion inhibitors do change the Stern-Geary constants, and that it is preferable to determine Stern-Geary constants experimentally prior to each corrosion rate measurement.