Transmission electron microscopy (TEM) microstructural characterization and microchemical analysis are two tools which can help relate proton exchange membrane (PEM) processing and resulting structure to fuel cell performance as well as structural changes to performance loss. A necessary first step is the preparation of specimens suitable for TEM characterization that maintain the spatial relationships among the various macro- and microcomponents of an entire PEM fuel cell. By carefully keeping the structure intact during the sample preparation, valuable information regarding the relationships among the many components of the fuel cell can be preserved. Previous TEM studies of PEM fuel cells have only been conducted on parts of the cell. No single preparation technique has resulted in keeping the entire fuel cell intact to image the entire cross section. In the present work, diamond knife ultramicrotomy has successfully been used to create thin sections suitable for TEM of entire PEM membrane electrode assemblies both before and after use in a fuel cell test stand. (C) 2003 The Electrochemical Society.