Mixed metal oxides are discussed as possible substitutes for noble metals in automobile catalytic converters. The catalytic activity for CO oxidation of LaMnO3 and La0.5Sr0.5MnO3 catalysts was examined.The ability of these catalysts to provide lattice oxygen and to sustain the oxidation reaction, even in the absence of molecular oxygen, has been confirmed. Measurements were performed of the reversible oxygen uptake on the two catalysts.