This paper describes the results of an exhaust emission testing program conducted on thirty-five 1979 passenger cars. The primary purpose of this program was to examine the emission performance of high-mileage vehicles. Secondary objectives included an assessment of the condition and performance of the emission-related components and adjustments and information for development and improvement of I/M programs. The work was performed by Automotive Testing Laboratories (ATL) at the Transportation Research Center in East Liberty, Ohio. The results of this program indicate that these vehicles are capable of maintaining low emission levels although high levels are also possible due to emission control component failure, engine wear, deterioration and tampering.