In a fuel cell stack, the current-free spot induces the variation of potential along the end faces of the bipolar plates clamping the defective cell. Numerical model shows that measuring these voltage shapes one can identify the presence of the spot and locate position of the spot center. Possible development of spot tomography in stacks based on this technique is discussed. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.