An important parameter in normalizing activities of porous electrocatalysts is real surface area of the catalyst. In this study CO stripping voltammetry was applied for the determination of the surface area of PtRu catalysts in a membrane electrode assembly. The difficulties in applying this method are summarized and a practical solution for the "accurate" voltammetric CO charge determination is suggested. The influence of adsorption time, potential, sweeping range and sweep rate on voltammetric CO charge determination is studied. It is shown that the CO charge determined in this way is independent on the sweep rate applied. (c) 2007 Elsevier Ltd. All rights reserved.