In order to investigate non-linear and non-stationary electrochemical systems, this series of two papers describes a new measurement method for electrochemical impedance spectroscopy (EIS), using specially designed broadband excitation signals. During one single experiment. the impedance, the level of the disturbing noise, the level of the non-linear distortions, and the level of the non-stationary behaviour are simultaneously measured. Part I of the paper presents the measurement strategy and validates it on a linear and a non-linear electrical circuit. In part II the described measurement strategy is applied to the pitting corrosion of aluminium (99.5 wt.%) immersed in an aerated sodium chloride solution. (C) 2004 Elsevier Ltd. All rights reserved.