Analysis of experimental EIS data in terms of equivalent circuits is the common approach used in most commercial software dedicated to EIS method. However, one-to-one assignment of impedance elements to particular electrochemical/physical processes causes difficulty, at the exception of the impedance calculated for one-step reactions. The example of EE reaction is dealt with in this article for the purpose of illustrating non-intuitive and sometimes unexpected features of equivalent circuits derived for a two-step electrochemical reaction involving only soluble diffusing species and electrons. (C) 2014 Elsevier B.V. All rights reserved.