Abstract: A method for the rapid determination of corrosion rates on a metallic material immersed in an electrolyte employs an electrochemical cell including at least one electrode of the material whose corrosion rate is to be determined and at least one other electrode also immersed in the same electrolyte. External forcing and measuring circuits are provided by means of which a first potential may be impressed across the immersed electrodes and the resulting current flow measured; the same circuits are also employed to impress a second potential and to measure the resulting current. Both said first and second potentials are so selected that they lie within the characteristic of the corroding cell governed by the exponential Tafel relationship. The freely corroding current for the test electrode is then determined by extrapolating the Tafel curve to zero impressed potential. The freely corroding current is then manipulated graphically or mathematically to give the corrosion rate in appropriate units.