This paper presents results from a study on speciation of the emission profiles and on the ozone forming potential of heavy-duty diesel exhaust under steady state engine operation. Very limited attempts have been made at determining the ozone forming potential of heavy duty diesel exhaust emissions. In this study a proportional sample of the dilute exhaust was drawn from a CFV-CVS system using a temperature controlled sampling line. The particulate matter was collected on a 70 mm Teflon coated glass fiber filter (TX40HI20WW), the semi-volatiles on XAD-2 copolymer resin and volatiles in Tedlar bags. The samples were analyzed by gas chromatography after conditioning and chemical extractions.The initial phase of the study was directed towards developing techniques and establishing protocols to determine the ozone forming potential of heavy-duty diesel exhaust. A pre-chamber naturally aspirated engine was tested on steady-state modes 1, 3, 5, 7 and 8 of the ISO 8 mode cycle. Mass emission rates and grams of ozone (potential) are presented for the volatiles, semi-volatiles and the particulate bound organics and also for the total exhaust. Emission rates of individual species within the volatiles, semi-volatiles and particle bound organics are also presented.The maximum ozone forming potential (263.0 mg ozone/Bhp-hr) was attributed to exhaust emissions under steady state, rated speed and 50% load conditions with the 27.7% aromatic content fuel. The highest mass emission rates of hydrocarbons (402.89 mg/Bhp-hr) were also obtained at rated speed and 50% load conditions.