The aim of this report is to scrutinize the thin-film rotating disc electrode (TF-RDE) method for investigating the electrocatalytic activity of high surface area catalysts. Special emphasis is given to the oxygen reduction reaction (ORR) on carbon-supported platinum catalysts. On the basis of measurements on four different Pt catalyst samples with various average particle sizes, it is demonstrated in detail how the intrinsic properties of the catalyst, i.e., the mass activity (A/g(Pt)) and the specific activity (A/m(Pt)(2)), are evaluated. The potential sources of error are critically discussed and guidelines for the measurements are given. Furthermore, the specific ORR activities determined for the different catalyst samples are analyzed and compared to polycrystalline Pt. The previously reported effect of the particle size on the specific activity for the ORR is interpreted on the basis of the shift in the potential of zero total charge and the concomitant alteration of the adsorption properties. (C) 2007 Elsevier Ltd. All rights reserved.