The long-term stability of the oxygen exchange properties of the IT-SOFC cathode materials La0.6Sr0.4CoO3-delta and La0.58Sr0.4Co0.2Fe0.8O3-delta vs. chromium poisoning is investigated at 600 degrees C by in-situ measurements of the chemical surface exchange coefficient of oxygen k(chem) using the dc-conductivity relaxation method. The as-prepared samples show high values of k(chem), which decrease moderately during the treatment in a dry atmosphere during 1000 h without and with the presence of a Cr-source. Humidification of the carrier gas results in a strong decrease in k(chem) of both materials. Post-test surface analysis of the degraded specimens by X-ray photoelectron spectroscopy identifies Cr- and Si-poisoning as well as Sr- and O-enrichment in depth ranges of about 100 nm as the origin of the degradation in a humid atmosphere. These results can be correlated with the strong enhancement of the gas phase transport of volatile Cr- and Si-species in the presence of H2O(g). It can be concluded that La0.6Sr0.4CoO3-delta (and to a lesser extent La0.58Sr0.4Co0.2Fe0.8O3-delta) cathodes retain a relatively high stability of the chemical surface exchange coefficients of oxygen at 600 degrees C in dry atmospheres, even in the vicinity of Cr- and Si-sources. However, significant performance degradation of (La, Sr)(Co, Fe)O3-delta-based cathodes has to be expected in humid atmospheres. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.027206jes] All rights reserved.