In this work, the effect of the depletion of oxygen in the cathodic chamber of a MFC operating in steady-state conditions has been studied To do this, several aeration-oxygen depletion cycles were repeated with a bring-back period of 1 day between them to let the system to re-establish its normal operation conditions During the depletion of oxygen from the cathodic chamber of a MFC operation results were found to progressively decay with the decrease of the oxygen concentration available to be reduced on the cathode, but electricity (42 mW/m(2)) was still produced for a nil dissolved oxygen concentration, due to the consumption of nitrates. The re-start up of the aeration in the cathodic chamber after a depletion stage improved the cell performance, but it did not recover completely its initial regime The repetition of aeration-oxygen depletion cycles led to a significant deterioration in the MFC performance, especially in the electricity produced just after the re-start of the aeration However, it did not affect to the long-term performance of the MFC during the oxygen depletion stage, and neither to the values of the oxygen and nitrates uptake rates measured during the aerobic and oxygen depletion stages. respectively (C) 2010 Elsevier Ltd All rights reserved