The first year's effort was concentrated on validation of the sample collection and analytical techniques and a survey of the PNA content of U.S. diesel fuels. A collection system consisting of a precooler, a glass fiber particulate filter, and a Chromosorb-102 trap was used to collect PNA's from diesel exhaust. PNA's are removed from the collection system by solvent washing and soxhlet extraction, concentrated, and analyzed by thin layer chromatography. Attempts to validate the sample collection system using C(14) tracers were not successful. Radio tracers also indicate that PNA-destroying reactions occur even after collection and extraction from the sample system. Similar losses of PNA's do not occur with synthetic exhaust. The fuel analyses showed that ASTM 1-D diesel fuels are nearly free of PNA compounds. PNA levels in ASTM 2-D diesel fuels ranged from near zero to values that reach the average concentration reported in motor gasolines.