The results of impedance measurements on stainless steel 304L by classical and dynamic electrochemical impedance spectroscopy (DEIS) have been presented. The investigation was focused on a transition of steel from passive state to the initial stage of pit formation. Based on the evolution of electrical parameters of the equivalent circuit it has been stated that the most probable mechanism of pit creation is the film-breaking model. (c) 2004 Elsevier Ltd. All rights reserved.