Alumina-supported nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum are active at 100 °C for butene isomerization in the absence of molecular hydrogen, and for an isotopic exchange reaction between gaseous hydrogen and hydrogen atoms associated with the support. Relative isomerization activities have been determined qualitatively and, with the exception of platinum, the activity sequence is independent of the phase of alumina used as support. Nevertheless, the alumina support appears to be an essential constituent of the catalyst if butene isomerization is to be achieved. Mechanism is not studied in detail, but it is likely that hydrogen atoms which migrate from the support to the metal initiate butene isomerization at the metal surface.