Investigations on the use of an exponential relaxation technique for studying corrosion systems are reported. It is shown that the polarisation resistance and the double layer capacitance of corrosion systems can be obtained by the small amplitude exponential relaxation technique (laert). It is demonstrated, that the rate of corrosion can be measured by the large amplitude exponential relaxation technique (laert). This technique yields ‘accelerated Tafel plot’ only when the charging current is negligible, which is seldom so. Methods for correcting for double layer charging are described. Double layer capacitance as a function of potential is obtained fromlaert. Therefore it can be used for studies on inhibitors. The utility oflaert for corrosion systems with only one of the conjugate reactions under activation control is established. The effect of series resistance (R_e) is discussed and anin situ method for its determination is described. A procedure for correcting the experimental data for errors due toR_e is given.