The modern Diesel engine is one of the most versatile power sources available for mobile applications. The high fuel economy and power of the Diesel engine has long made it the choice for heavy-duty applications worldwide. Over the coming years, global emissions legislation applied to heavy-duty Diesel (HDD) engines will become more and more stringent, necessitating the use of advanced emissions control technologies. In particular, the coming exhaust gas emissions legislation focuses on particulate matter (PM) emissions and emissions of nitrogen oxides (NOx).A filtration device can control PM emissions, and a possible technology for the abatement of NOx emissions involves NOx absorber catalysts. This paper describes investigations into the activity and system behaviour of a prototype HDD exhaust system based on NOx absorber technology. The system consists of a “single leg” containing NOx absorber catalyst that is bypassed during rich regeneration of the NOx absorbers. NOx conversions obtained on both SET and FTP cycles were 79% and 67% respectively. The effect of system design and hardware changes on the NOx performance is discussed. Initial investigations into the sulfation and desulfation behaviour of the NOx adsorber system are also reported.