This study focuses on the even harmonic current response for a reversible electrochemical system, which is subjected to a large amplitude square wave voltage signal. On the basis of both theoretical considerations and low frequency experiments it is shown that the even harmonic contributions to the overall response are essentially non-existent over the entire range of dc-potentials, provided that an almost perfect square-wave perturbation is employed. These results are important for the continuing investigation of the large amplitude square wave voltammetry. (C) 2003 Elsevier Science B.V. All rights reserved.