The influence of injection pressure (IP), start of injection (SOI) and exhaust gas recirculation (EGR) on the aerosol exhaust particle size distribution emitted by a state-of-the-art Heavy Duty Diesel engine was experimentally investigated. Increasing IP was found to reduce the accumulation mode particle number and favour the formation of nuclei mode particles. The application of EGR produced the suppression of the nucleation mode and an increase in the accumulation mode particle number. Advanced SOI reduced slightly the accumulation mode without variation of the count median diameter (CMD). The impact of the engine parameters on the size classes of the distributions and the sensitivity to progressive variations of the factors were examined. A correlation study showed that there is a relationship between the particle number and the CMD of the size distributions obtained at equal engine operating conditions, independently of the engine strategy applied. (C) 2005 Elsevier Ltd. All rights reserved.