INTRODUCTION Concern for air pollution has shifted from major pollution sources@ first subjected to control measures@ to include those of lesser magnitude as the major sources have come under control. Diesel engine exhaust is still a minor factor in pollution in the United States. But because the diesel engine produces both smoke and odor in the exhaust@ attention to this problem area is justified. Polynuclear Aromatic Hydrocarbons (PNA) do not appear to occur naturally in the environment but have been associated with combustion processes. (1@ 2)* Ray and Long (1) state that PNA is associated with soot formation and inefficient combustion. Bailey@ et al(2) states that PNA in diesel engines is associated with overfueling. A Public Health Service(3) study indicated that hand fired coal burning combustion sources are the most important source of BaP emissions in the United states. Much lower emissions were estimated for all other combustion sources including motor vehicles. An important investigation of the automotive vehicle contribution to BaP levels in the atmosphere has been completed by Colucci and Begeman.(4) They showed that vehicular contributions to total PNA levels could account for between 5 and 42% based on correlations with lead measurements. In another study@ these authors(5) showed that BaP in the fuel can survive the combustion processes in a gasoline engine (up to 36%). Gross(6) in a study for the CRC-APRAC@ showed that PNA emissions from gasoline engines were influenced by (a) emission control systems@ (b) PNA in fuel@ and (c) oil consumption rate. Work has been started to determine the effect of operating conditions on PNA emissions and to establish the repeatability of the 3. Work has been started to determine the effect of operating conditions on PNA emissions and to establish the repeatability of the overall procedure. Future work will concentrate on measurement of PNA emissions from other types of diesel engines and on identifying the effects of specific operating conditions@ blowby@ deposits@ lube oil@ and fuels. *Numbers in parenthesis designate References at end of report.