A simple fatigue model for perovskite ferroelectrics is developed based on electric field driven point defect drift. At room temperature significant point defect cluster growth only occurs if diffusion is enhanced by an electrically supported drift mechanism. In order to achieve a significant charge carrier drift considerable parts of the depolarizing field have to be temporarily unscreened. These unscreened local environments can only occur under a bipolar duty cycle just before complete reversal of the domain system. The case of the oxygen vacancy as an ionic defect is modeled. (c) 2006 Elsevier B.V. All rights reserved.