The single and combined effects on catalyst stability, activity and selectivity of iron and calcium metal-organic contaminants deposited on a fluidized catalytic cracking (FCC) catalyst via a cyclic deactivation treatment have been studied. It has been found that iron contamination decreases catalyst activity by two different mechanisms. At low iron concentration the deactivation is mainly due to the direct poisoning of acid sites while at higher iron concentration the deactivation is mainly due to pore blocking. Moreover, iron clusters formed on FCC catalyst particles catalyze dehydrogenation reactions which lead to a higher coke selectivity. Calcium contamination is also at the origin of a large deactivation of the FCC catalyst which occurs by neutralizing acid sites and in a large extension by lowering the hydrothermal stability, at the origin of an important collapse of the zeolitic component. The combined contamination by iron and calcium does not show synergetic effects. Nevertheless, the fact that coke formation increases with iron can enhance the catalyst temperature in the industrial regenerator, leading to a further negative effect of calcium via zeolite destruction. (C) 2013 Elsevier B.V. All rights reserved.