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Ruthenium-containing catalysts have good activity and selectivity for the reduction of the nitric oxides in automobile exhaust. Although designed to be operated under reducing conditions, these catalysts lose Ru by volatilization when subjected to lean transients. Attempts were made to stabilize these catalysts against volatilization by forming stable ruthenates. This paper deals with durability testing of stabilized ruthenate catalysts on a laboratory bench set-up, dynamometers, and vehicles. Post-mortem analysis of the durability-tested catalysts are presented showing the extent of stabilization. The results show that the Ru loss from ruthenate catalysts in present vehicle systems is in excess of acceptable limits. These losses can be minimized further, but at a cost of reduced selectivity in the NO reduction. Substantial further improvements are needed to achieve the required performance characteristics. Another problem is the poisoning by S, Pb and P.