More stringent emission legislation has been a driver for changes in the design of Heavy Duty Diesel engines since the 1980s. Optimization of the combustion processes has lead to significant reductions of exhaust emission levels over the years. However, in the year 2002, diesel engines in the USA will have to meet an even more stringent set of emission requirements. Expectations are that this will force most engine builders to incorporate Exhaust Gas Recirculation (EGR).Several studies of the impact of EGR on lubricant degradation have shown increased levels of contamination with soot particles and acidic components. Both of these could lead to changes in lubricant requirements. The industry is developing a new specification for diesel engine lubricants, PC-9, using test procedures incorporating engines with EGR.This paper discusses the development of one of these new engine test procedures, the Mack T-10, a test primarily intended to evaluate lubricant performance in the areas of piston ring and liner wear, and bearing corrosion. A two-phase test procedure was developed in which the engine is run for 75 hours at operating conditions that promote lubricant degradation followed by 225 hours at conditions that generate liner wear. It has been demonstrated that the 300 hour test is capable of discriminating lubricants with known performance.