Pore-free microelectrodes (20-100 mu m diameter, 100 nm thick) of mixed-conducting perovskites are prepared on dense pellets of Y-doped BaZrO3 (4-15% Y) as proton-conducting electrolyte. The oxygen reduction reaction is investigated in gas-symmetric cells using AC impedance spectroscopy. The electronic resistance owing to the non-negligible hole conductivity of acceptor-doped BaZrO3 in oxidizing atmosphere can - even though much larger than the ionic resistance - be much lower than the resistance of the oxygen exchange reaction. This results in a substantial impact of electronic leakage current on the impedance spectroscopic investigations of the oxygen reduction process. Solutions to this problem are demonstrated. The impact of this effect for porous electrodes is discussed. (C) 2013 Elsevier B.V. All rights reserved.