Five different diesel fuels, having been made available by the mineral oil industry within the framework of a research program of the Coordinating European Council (CEC/PF-26), were examined in addition to this program by the Klöckner-Humboldt-Deutz AG by means of the 13-mode test in accordance with the former US legislation and the ECE regulation No. 49 and by US Transient Tests. The results have been compared with results based on commercial European diesel fuel. There has been observed the emission behaviour of an 8-cylinder NA engine with a “state of the art” direct fuel injection system by particularly taking into consideration the particulate emission and the particulate components.The gaseous emissions, particularly CO and HC, are unfavourably influenced by low cetane numbers being associated with increased aromaticity in the diesel fuel. The emission of particulates is increased by low cetane numbers and additionally, to a somewhat lesser extent, by high boiling portions of the fuel. This increase is nearly exclusively taking place on penalty of condensed portions of unburnt fuel when taking into account the various particulate fractions in a differentiated manner. A large fuel influence has been observed for the emission of polycyclic aromatic hydrocarbons.From the results obtained, there is to be derived the requirement to combine a legally specified minimum quality for diesel fuel with legally specified limit values for the emission of particulates.