Preliminary evaluations indicated that the Perfect Circle Retronox device caused substantial reduction in total oxides of nitrogen emissions from passenger vehicles. Evaluation of the effectiveness of the device was initiated. The vehicles were tested both in baseline and device equipped configurations by the 1972 Federal emission test procedure. The Retronox system demonstrates significant effectiveness in reducing oxides of nitrogen. In general these emissions can be reduced by over 50%. There also appears to be a smaller yet consistent reduction in hydrocarbon and carbon monoxide possibly resulting from increased fuel-air mixing hence more homogeneous delivery to the individual cylinders. It is anticipated that installation of the system will result in decreased fuel economy. Little adverse effect on driveability was noted or anticipated.