The promoting effect of metal cations addition to SO42--ZrO2 in n-butane isomerization is studied. Several metal cations (Pt, W, Ni, Co, Fe, Cr) supported on SO42--ZrO2, or in an inert material mechanically mixed with SO42--ZrO2, produce an increase in the rate of n-C-4 isomerization. Cu has an inhibiting effect. The metals or their oxides provide the dehydrogenation capacity that can produce C-4 alkenes, which in turn can influence the mechanism of isomerization. These C-4 alkenes can be added to the pool generated by the strong Lewis acid-base pair of SO42--ZrO2 leading to an increase in the isomerization rate.