INTRODUCTION This report concludes the second year of a research program to chemically identify the odor components of diesel exhaust. The study is sponsored jointly by the Coordinating Research Council and the National Air Pollution Control Administration@ U.S. Public Health Service@ as part of their continuing support of programs designed to obtain a detailed technical understanding of diesel exhaust and its odor. During the first year of the program@ we developed an experimental approach1 which involved sensory characterization as an integral part of the study. We also developed methods for collecting large volumes of diesel engine exhaust by condensation at 0?? extracting the organic portion of the exhaust condensate@ and separating the odorous components of the extract from the non odorous (and major) portion by liquid chromatography. The odorous species separated into two major odor fractions with roughly equal odor intensities - oily-kerosene and smoky-burnt. At the completion of the first year's study we were developing methods for resolving both of these odor fractions into single species for odor description and chemical identification. A two-stage gas chromatography (GC) approach demonstrated promise for the final resolution. 1. Chemical Identification of the Odor Components in Diesel Engine Exhaust@ final report July 1969. CRC Project CAPE-7-68. HEW CONTRACT PH 22-68-20.