Through measurement of Cu2+ species via electron paramagnetic resonance (EPR) we detected changes in the distribution of Cun+ sites in Cu-ZSM-5 samples used in the selective catalytic reduction of NO with C3H8 in the presence of H2O at 673 K. In samples used under dry or wet operation for short periods of time, Cu2+ species were evenly distributed between square planar and square pyramidal environments. Operation under wet conditions for periods of the order of tens of hours caused a third Cu2+ species to be formed, presumably located in a recessed location in the zeolite. At the same time, irreversible deactivation was manifest, suggesting an association between those events. Neither structural changes nor dealumination of the zeolite were detected in our studies, indicating that deactivation was caused only by changes in the distribution of Cun+ sites.