The initial deactivation occurring during conversion of methylbutunol on basic alkali-faujasite catalysts was studied by microGC. Both the product selectivity and the formation of water during the first minutes of run permit to conclude on the deactivation process and on the nature of the adsorbed inhibiting products that were also identified by in situ thermal activation in O2 or N2 of used catalysts, followed by mass spectrometry. Interestingly, the level of activity at steady state after thermal regeneration in O2 is significantly higher than on the fresh catalyst.