A planar cell design for free-breathing fuel cell is studied. The cathode side of the cell was directly open to ambient air in a way that oxygen needed by the fuel cell reaction was provided by diffusion through the cathode side gas diffusion backing, i.e. the cell had no cathode side flow channels. The aim of the study was to demonstrate the feasibility of the cell concept by experimentally evaluating its performance with polarisation and current transient measurements. The orientation of the cell did not significantly affect the performance of the cell and signs of flooding were not observed. The maximum power density achieved in the polarisation measurements was similar to124 mW cm(-2). The current transient measurements revealed that with a small base load the cell is capable of producing momentarily current densities up to 500 mA cm(-2). The maximum transient power density achieved was similar to194 mW cm(-2) at transient current density of 450 mA cm(-2). According to the results it seems that this kind of cell design is feasible for small-scale applications, such as portable computers. (C) 2003 Elsevier B.V. All rights reserved.