The effect of Ni and V in the hydrothermal deactivation of an ultrastable Y zeolite with and without rare earth elements is presented and discussed. Although in the presence of steam, vanadium itself is the main factor responsible for zeolite loss of surface area, for the rare earth containing sample the presence of nickel increased the vanadium effect. Temperature-programmed reduction of these zeolites further support this observation by showing an increased amount of mobile readily reducible vanadium species while nickel and rare earth interact. The same deleterious effect of nickel was also observed in rare earth containing FCC catalysts after hydrothermal deactivation. (c) 2005 Elsevier B.V. All rights reserved.