This study used electrochemical impedance spectroscopy (EIS) to characterize composite metal oxide electrodes in atmospheres containing NO, NO2, and O-2. Symmetrical cells with electrodes of (La1-xSrx)(s)MnO3 [(x, s)=(0.15, 0.9) and (0.5, 0.99)] and doped ceria [Ce0.9Gd0.1O2 and Ce1-xGdxO2 (x=0.1, 0.2)] were subjected to EIS while varying the temperature (from 300 to 600 degrees C), the composition of the atmosphere, and the gas flow. The impedance spectra were fitted to equivalent circuits, and common arcs were identified and sought related to physical and chemical processes. The electrodes had a much lower polarization resistance (R-p) when NO or NO2 was present in the atmosphere at low temperatures (300-400 degrees C) than in air. The impedance spectra for electrodes in 1% NO in Ar were dominated by a low frequency arc at high temperatures (500-600 degrees C). This arc seemed to be a type of conversion arc, which is related to a gaseous intermediate (possibly NO2), formed from NO, through which the electrode reaction occurs. Indications were found that the electrodes are not electrochemically active toward NO around open-circuit voltages.