The purpose of this effect is to gather information on catalyst-equipped passenger cars which have exceeded their defined 'useful life'. The following areas were to be addressed: (1) Emission performance in as-received condition, (2) Extent of malperformance in the emission control system, (3) Capability of restorative maintenance in reduction of emission levels, (4) Effectiveness of both old and new catalysts on emission levels. A total of eight catalyst-equipped passenger cars were procured from private owners in the St. Louis area. Vehicles of each of the three major domestic manufacturers were chosen to constitute the test fleet. The actual vehicles were sought to obtain a general representation of popular models and engines with the final selection based on odometer reading. Each vehicle was subjected to a prescribed series of tests, inspections and maintenance actions.