As part of an ongoing programme of Exhaust Gas Recirculation (EGR) wear investigations, this paper reports a study into the effect of Exhaust Gas Recirculation, and a variety of interacting factors, on the wear rate of the top piston ring and the liner top ring reversal point on a 1.0 litre/cylinder medium duty four cylinder diesel engine. Thin Layer Activation (TLA - also known as Surface Layer Activation in the US) has been used to provide individual wear rates for these components when engine operating conditions have been varied.The effects of oil condition, EGR level, fuel sulphur content and engine coolant temperature have been investigated at one engine speed at full load. The effects of engine load and uncooled EGR have also been assessed. The effects of these parameters on engine wear are presented and discussed.When EGR was applied a significant increase in wear was observed at EGR levels of between 10% and 15%. The wear increase was mirrored by an increase in the carbon content in the cylinder which had a fundamental effect on the piston ring and liner wear and on the oil quality. Therefore, wear occurring at any point in time was a function of the soot loading of the oil and soot loading of the combustion chamber, rather then simply the level of EGR. Corrosion induced wear with EGR did not appear to be significant with current fuel.This has significant implications for Euro IV, or similar emission levels, which are achieved through the use of EGR. To meet these emissions, soot levels will be significantly lower than those of the test engine. This will substantially reduce the soot level in the cylinder and reduce the oil ageing effect. It is therefore possible that future low emission engines, using high levels of full load EGR, may not produce the levels of soot seen in this study and therefore may have no EGR wear problems for the piston ring and liner.