The second stage of the PROCONVE emission legislation, which is effective since model year 1992, was met by various of the Brazilian carmakers through the application of open loop three-way catalysts.As a result of intensive test and development programs, different open loop three-way catalyst designs were selected for ethanol and gasohol fueled vehicles, so as to reach the required emission reduction performance at optimized costs. For the ethanol fueled vehicles, the new washcoats developed allowed precious metal formulations without rhodium. The durability of these systems is supported by the properties of the fuel, since ethanol is basically free of sulphur and lead.For the gasohol fueled vehicles, a Pd/Rh formulation is applied, along with washcoats which guarantee an emission reduction performance in a broad range of A/F engine operation conditions.The paper reports the evaluation results of these catalysts on engine benches as well as on vehicle dynamometers, using the US-FTP 75 test procedure. The evaluation was performed with fresh catalysts, with catalysts aged on the engine bench as well as with catalysts aged on vehicles in the AMA durability cycle for more than 80.000 km driving. A detailed physico-chemical characterization was performed on the catalysts after usage to identify the deactivation mechanisms. The results of these studies show that the exhaust aftertreatment concepts chosen are viable means to meet the goal of the second stage of the PROCONVE program. The experience gained will be a solid basis for the development of systems including powertrains and catalytic aftertreatment to meet the third stage of this program.