Summary: The petrography and mineralogy of a series of gabbroic xenoliths, consisting essentially of varying proportions of olivine, clinopyroxene, ortho-pyroxene, and plagioclase, are described from Gough Island. These are compared with xenoliths from other oceanic localities. Four new analyses of xenoliths and six of pyroxenes are presented, together with some partial analyses of plagioclases. It is concluded that the xenoliths are derived from the mantle above the magma source area. The composition of the mantle in this region is thought to be that of an olivine-tholeiite.