Nonstoichiometric nickel-copper spinel manganites were found to be highly active for the reduction of nitric oxide by carbon monoxide at low temperature (300 degreesC). The activity increases with the level of nonstoichiometry of the oxides and almost linearly with their specific surface area. Moreover, this activity was found to depend strongly on the copper content, nickel manganites being almost inactive. The influence of the surface state of the oxides was also investigated. Cuprous cations are thought to play the determining role in the catalytic cycle.