This work concerns exhaust gas cleaning for heavy-duty diesel engines by means of NOx storage and reduction technology. A full-scale engine rig has been constructed and stationary NOx reduction tests performed.In the NOx storage and reduction approach, NOx is stored on a BaO surface as Ba(NO3)2 under long lean conditions and desorbed and reduced under short rich conditions. The rich conditions are created by injection of diesel fuel into the exhaust stream. The stationary NOx reduction tests have been performed at nine load points on an engine rig. They have shown that a stationary NOx reduction of between 25-53% is achievable at most load points depending on the temperature.The high oxygen content in the exhaust gas leads to the oxidation of the injected hydrocarbons and thus to a high fuel penalty. To lower the fuel consumption, the mass flow through the catalyst has been reduced under the regeneration periods. This was done using a bypass system with a pneumatic valve control. The extent of the reduced catalyst flow has been examined.