This paper presents a control approach to the air feed of a fuel cell based on a single input single output sliding mode control. Fuel cells are electrochemical devices that generate electrical energy from chemical reactants and are good candidates for clean energy generation, since the waste product is water. An efficient operation of fuel cells depends on a good control strategy for the air supply system. The controller obtains its nonlinear behaviour through a variable structure strategy, whose tuning is proposed by making use of a low-order linear model of the process. This structure allows the real-time implementation of a robust control law that is able to deal with the nonlinearities and uncertainties without the need of heavy computation load for the controller algorithm, while allowing a fast sampling rate according to the needs of these power systems. The performance of the control scheme proposed is successfully evaluated on a medium-size PEM cell fuel. (C) 2009 Elsevier Ltd. All rights reserved.