An engine test unit for the evaluation of Diesel exhaust filters with analytical equipment to measure particulates, oxygen, hydrocarbon, carbon monoxide, nitrogenoxides concentrations, temperature and pressure trends is described as well as the test procedures presently applied.Engine test results with different types of Diesel particulate filters -non activated and catalytically activated - up to 400 hrs. operation time are presented. With base metal catalysts, reductions in “soot”-ignition temperatures of about 100 °C could be attained under optimal conditions. A correlation between oxygen concentration in the exhaust gas and the “soot”-ignition temperature is demonstrated. Combined catalytic systems (precious metal and base metal catalysts) permitted hydrocarbon and carbon monoxide conversions up to 90 % - including a decrease in odour intensity - in addition to particulate reduction.