Anode-supported solid oxide fuel cells (SOFCs) based on Ni-yttria-stabilized zirconia (YSZ) anodes, YSZ electrolytes, and lanthanum strontium manganite (LSM)-YSZ cathodes were studied with respect to durability in humid air (similar to 4%) typically over 1500 h. Operating temperature and current density were varied between 750 and 850 degrees C and 0.25-0.75 A/cm(2), respectively. The introduction of humidity affected the cell voltage under polarization of the cell, and this effect was (at least partly) reversible upon switching off the humidity. Generally, the studied cells were operated in humid air under technologically relevant conditions over more than 1500 h. Improvements at the cathode/electrolyte interface made it possible to obtain highly stable cells, which can be operated under high current density and at 750 degrees C in humid air, conditions that cause significant cell voltage degradation in dry air on cells with LSM/YSZ-based cathodes. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3459904] All rights reserved.