Platinum/carbon nanotubes (Pt/CNT) electrocatalysts are prepared. The CNTs are pre-treated in order to obtain reactive sites for the adherence of Pt metal particles. The electrocatalysts are characterized by scanning electron micrograph (SEM), transmission electron micrograph (TEM) and X-ray photoelectron spectrum (XPS) measurements. It is found that the catalysts contain both Pt(O) and Pt(IV) species. A high Pt loading of 32.5% on CNTs is obtained when the catalysts are prepared with ethylene glycol and Pt salt. The electrocatalysts are used for the oxygen reduction reaction in polymer electrolyte membrane fuel cells (PEMFCs) and the performance of PEMFC is analyzed with respect to catalyst synthesis and Pt loading. Cyclic voltammetric studies show that the Pt utilization in the fuel-cell electrodes is around 44%. Catalysts obtained with mild nitric acid-treated CNTs give a better performance of 680 mV at 500 mA cm(-2) and 600 mV at 800 mA cm(-2) than catalysts prepared with ethylene glycol and Pt salt. (C) 2004 Elsevier B.V. All rights reserved.