Zeolites can deactivate by coke laydown and by poison deposition. Here we consider a simple reaction, the cracking of cumene, over a simple zeolite, type Y, as deactivated by coke deposition and the presence of sodium. We show that the effect of coke level and sodium level can be treated in a unitary manner. This allows the relative magnitudes of coking and poisoning to be quantitatively compared. By coupling this information with what is known about the structure of poisons on active sites, details can be obtained regarding the structure of coke on the active site.