The conventional method of catalyst endurance testing on vehicles is unsuitable for large-scale catalyst development, since the time and cost are prohibitive. This paper reviews a series of experiments comparing the effects of two methods of engine test-bed aging on catalyst deterioration with the normal vehicle endurance test. The test-bed engines caused a higher rate of catalyst deterioration than the vehicle, and there are indications that this effect is related to the intake mixture strength of the engine.From these experiments, a technique for accelerated catalyst aging was derived. The reactor is aged on a test bed for three periods, each of 100 h. At the 0, 100, 200, and 300 h stages, the reactor is removed from the test bed and transferred to another engine for detailed tests of catalyst performance. A 1975 CVS test on a vehicle is also included in each set of experiments. Results from some of the catalytic reactors, tested by this technique, are presented.