The emission reduction potential of high boost and high injection pressures was investigated on a 4-cylinder small bore diesel engine at high rates of exhaust gas recirculation. For this reason an external boosting system was built up, which allowed to generate the desired boost pressure independent from the engine's operating point. In order to simulate conditions comparable to a real turbocharged engine, also the influence of the turbine on the exhaust back pressure was considered. The whole measurement campaign was carried out at two load points (low- and mid-load), which represent characteristic engine operating points of the Urban Driving Cycle (UDC).On the one hand could be shown, that there is an enormous potential in the reduction of particulate matter (PM) up to 75 % and of carbon monoxide (CO) up to 15 % at the mid-load point by increasing the boost pressure. In combination with a high injection pressure the PM emissions could be further reduced up to 95 % compared to a single-stage turbocharged engine. However the increase in boost pressure resulted in a slight disadvantage in the emissions of unburned hydrocarbons (HC).On the other hand the increase in boost pressure resulted only in a disadvantage in the PM emissions up to 65 % at the low-load point. This deterioration could however be compensated by increasing the injection pressure, so that a total reduction in the PM emissions up to 80 % was achieved.The CO emissions could be reduced up to 35 % by increasing the boost pressure with a simultaneous advantage in the HC emissions of about 10 %.All results were achieved without a disadvantage in the brake specific fuel consumption.