The conversion of 1-butene over Pt-ZSM5 was studied in the presence and absence of hydrogen. In the absence of hydrogen, the catalytic activity of the metal was rapidly poisoned and in the steady state the catalyst showed identical properties as the parent ZSM5. In the presence of hydrogen, the skeletal isomerization of butene was not affected, but the rate of oligomerization/cracking was enhanced. From the by-products butadiene, propane, ethane and methane, ethane and propane originated mainly from oligomerization/cracking on the acid sites and not from hydrogenolysis on Pt. The contribution of the metal to the overall by-product formation was small. Thus, an adaptation of the acid rather than of the metal sites is necessary to improve the performance of the bifunctional catalyst.