First-row transition metals were tested in a flow reactor as promoters of sulfated zirconia for the isomerization of n-butane at 373 K and 0.005 bar n-butane partial pressure. The activity of each of the sulfated zirconia samples increased through a maximum and then decreased with time on stream. In order of increasing activity measured at the maximum, the effect of the promoters increased from right to left in the periodic table : zinc, nickel, cobalt, iron, and manganese. Iron and manganese increased the activity by 2-3 orders of magnitude. The causes of the promoter action are not elucidated; the promoters may play noncatalytic roles as initiators.