NADH and succinate oxidase activities of inside-out submitochondrial particles treated with excess oligomycin are inhibited by lanthanides (La3+ and Dy3+). Inhibition by both oligomycin and oligomycin plus lanthanides is completely relieved by an uncoupler. The respiratory control, measured as the stimulation of NADH or succinate oxidation caused by the addition of uncoupler to the oligomycin-treated particles, is thus increased in the presence of lanthanides. The coupling effect of lanthanides is completely prevented and rapidly reversed by excess of EDTA. La3+ increases the extent of the aerobic energy-linked succinate-supported NAD+ reduction catalyzed by the oligomycin-treated submitochondrial particles. Lanthanides seem to be a useful tool to increase the energy coupling capacity of the submitochondrial particles.