The dynamic performance of a laboratory fuel cell system based on a 20 kW H-2/air proton exchange membrane (PEM) stack was investigated on test cycles compatible with automotive applications, with particular reference to the effect of different air management strategies on cell voltage uniformity and fuel cell system efficiency. The air management strategies were varied by imposing different stoichiometric ratio values as function of stack current, and were studied on two test cycles characterized by current variation rates ranging from 2 to 50 A/s, with maximum stack current of 240 A. Stack temperature and reactant pressure during the tests were maintained below 330 K and 150 kPa, respectively. The best compromise between fuel cell system efficiency and dynamic response in terms of cell voltage regularity was obtained with an air management strategy characterized by stoichiometric ratio values slightly superior to those optimized for steady state conditions. This management strategy determined an efficiency decrease in steady state conditions of maximum 3% for the sub-system stack + compressor in the range 0-200 A. The individual cell voltage uniformity was continuously monitored by a statistical indicator (coefficient variation C-v), which was always lower than 3% also at 50 A/s, indicating a satisfactory dynamic stack operation. (C) 2008 Elsevier Ltd. All rights reserved.