Beginning in 1996 the exhaust emissions of off-highway heavy-duty diesel engines between 130-560 kW (175-750hp) will be regulated by the EPA, (1). Along with the emission regulations comes the difficulty of establishing a set of standard test procedures which allow engine manufacturers and regulatory agencies to compare emissions data based on similar test methods. In order to remedy this problem, the International Organization for Standardization (ISO) has come up with an exhaust measurement procedure, ISO 8178, that can be applied worldwide to off-highway heavy-duty diesel engines, (2). The ISO 8178 procedure is based on steady-state operating modes combined with weighting factors that together represent a cycle for a specific engine application. The ISO 8178 test procedure allows the exhaust emissions to be sampled with either a full flow dilute or raw sampling system. However, the preferred sampling systems are the raw gaseous and mini dilution tunnel (MDT) particulate measurement methods. The main concern of these sampling systems is the demonstration of equivalency to the full flow dilution system that is currently used for the certification of on-highway heavy-duty diesel engines.Using an in-house full flow dilution system and a recently built raw gaseous emissions bench along with a pre-existing MDT, this research was conducted to find the correlation between the two sampling systems. For the gaseous emissions of HC, NOx) and CO the correlation between the raw and full dilution sampling systems was within 7.0%, 3.0%, and 1.0% respectively. The correlation between the MDT and full dilution particulate sampling systems was within 2.5%. Additional investigation was performed in the area of MDT transfer tube length and its effect on particulate measurement. An experiment was performed to quantify the effect of a wide range of water vapor concentrations on the measurement of NOx.