We have examined the adsorption of carbon monoxide and nitric oxide on model Rh/lanthana and Pt/lanthana catalysts using temperature-programmed desorption (TPD). First, the surface of lanthana can be reduced in carbon monoxide by forming the carbonate which decomposes above 650 K. Reduced lanthana adsorbs significant amounts of carbon monoxide and nitric oxide, both of which desorb in a similar temperature region to that found for rhodium and platinum. Substantial amounts of the nitric oxide on reduced lanthana react to form nitrogen and nitrous oxide. The addition of rhodium and platinum significantly promotes the reduction of lanthana, and a significant fraction of the carbon monoxide adsorbed on freshly deposited metal films forms carbon dioxide. Based on suppressed adsorption of nitric oxide on thin metal films, it appears that the metals are oxidized and the lanthana reduced immediately following deposition. The TPD curves on the reduced Rh/lanthana and Pt/lanthana appear to be a simple sum of the desorption from reduced lanthana and small metal particles, so that there is no evidence for new adsorption states which might indicate changes in the metal properties due to the presence of lanthana.