The role of cathodic cover opening ratio on water management was investigated for micro air-breathing polymer electrolyte membrane fuel cells (PEMFCs). The results demonstrate the possibility to manage water content in micro-PEMFC using cover opening ratio variation. By measuring the internal resistance of a cell in various cover configurations (0.33 Omega cm(2) to 4.0 Omega cm(2)), the influence of cover opening ratio on water management was shown. Indeed, for a cell situated in a 10% relative humidity atmosphere and operated at 0.5 V, the addition of a 5% opening ratio cover allowed to reach similar current densities (270 mA cm(-2)) to those recorded for the same potential at 70% relative humidity without cover. Although the starting current density for a cell operated at 60 degrees C without gas humidification was extremely low (15 mA cm(-2)), the total closure of the cover allowed to maintain the water produced and accumulated by the cell at the cathode, and current density of 800 mA cm(-2) were reached after height minutes of operation. The influence of the opening ratio on back-diffused water was also evaluated and the maximum of back-diffused water was observed for a cell operated with a 5% cover opening ratio and represented 33% of the total water product at 150 mA cm(-2). A new method of anodic water evacuation, which does not increase the cell volume and which does not require any control tool was carried out and experimentally evaluated. (C) 2009 Elsevier B.V. All rights reserved.