Much attention has been paid to the emissions from diesel transit coaches culminating in the 1990 EPA bus standard.(1)* A primary pollutant that has been singled out for advanced controls is diesel particulate. In order to meet the low levels of particulate emissions in the standard, diesel particulate filters are one of the principle methods being studied. To this end, the Ministry of Transportation and Communications of Ontario and Engine Control Systems Ltd. entered into a cooperative development program for a low cost, simple and retrofitable diesel particulate control system.(2)The paper outlines the various components of the system and the results of field testing.