The article reports on the results of a 780 h life test of high temperature MEA with PBI-H3PO4 membrane. The MEA was loaded by current density 0.2 A cm(-2) for 763 h at 160 degrees C in hydrogen-air feed. The load was discontinued 14 times during the life test including three complete shut downs. In the course of the life test MEA characteristics were studied by electrochemical methods. Pt particle size growth was evaluated by ex situ measurements of electrochemical hydrogen adsorption/desorption with the cathode catalyst sampled after the life test and with pristine catalyst. Possible changes of electrochemically active surface area (ESA) of carbon support were monitored by electrochemical impedance studies (EIS) performed in the course of the MEA life test. Average Pt particle diameter was found 3.8 and 7.8 nm for pristine catalyst and for catalyst sampled after the life test, respectively. ESA of carbon support remained unchanged, membrane resistance decreased by similar to 20%, hydrogen crossover increased by a factor of 14, although remained insignificant. Voltage loss rate in the life test was similar to 25 mu V h(-1). The major cause of the MEA degradation was identified as a loss of Pt ESA by particle size growth. (C) 2009 Elsevier Ltd. All rights reserved.