PURPOSE AND SCOPE With the growing attention on atmospheric pollution@ it has become increasingly desirable to obtain a detailed technical understanding of the chemical nature of those components of diesel exhaust which relate to odor. Coordinating Research Council@ and the National Air Pollution Control Administration@ U.S. Public Health Service have had an interest in this problem for many years@ as shown through their support of a variety of research programs. Most of the work to date has been oriented toward determining the chemical composition of diesel exhaust and studying the odor using olfactory techniques.1-3 Recently@ it became apparent that a greater understanding of the chemistry of diesel exhaust particularly related to odor was needed and research efforts in this direction were undertaken. Part of this effort has been in support of the present program at Arthur D. Little@ Inc.@ the purpose of which is to chemically identify the odor components of diesel exhaust. The objectives of the total program@ a part of which is described in this report@ are: (1) to determine the relative contribution of individual chemical species in diesel exhaust to the intensity and character of the exhaust odor; and (2) to describe these species in terms of chemical parameters. Broken down into several steps@ the program becomes: Step 1 Using olfactory techniques@ characterize the odor components in diesel exhaust with respect to their type@ intensity@ threshold values@ character@ and possible contribution to human irritation@ Step 2 Separate the odor components from the exhaust@ Finally@ it is recommended that similar programs be undertaken for the other odor notes so that suitable guidelines can be developed for removal of the major portions of the components of odor in diesel engine exhaust. 1. Diesel Exhaust Composition and Odor@ Scott Research Laboratories@ Final Report on Contract No. PH 86-67-134@ and earlier references cited therein. 2. An investigation of Diesel Powered Vehicle Odor and Smoke@ Southwest Research Institute@ Final Report on Contract No. 86-67-72 and earlier references cited therein. 3. Composition of Diesel Exhaust@ Reports to PHS from Bartlesville Petroleum Research Center@ Bureau of Mines@ U.S. Department of the Interior.