Only 2 of the 11 laboratories which have had diesel odor research projects underway during the last 16 years are still active in this research area. Much of the earlier work was devoted to developing diesel odor sampling, standards, and measurement techniques. Subsequently, work became generally focused upon the chemical identification of the odorants, a very difficult task due to their large number and low concentrations. After three years of concentrated effort involving the development of new odor measurement, sampling, and diesel exhaust analysis and preparation techniques, odorants comprising the two major diesel odor characteristics were identified. Compounds which are also components of diesel fuel were shown to contribute to one odor characteristic. Oxydized derivatives, generally of the same classes of compounds as those shown to contribute to the first odor characteristic, were tentatively identified by structure to comprise the second major odor characteristic. The recent work has resulted in the development of a laboratory prototype instrument for determining diesel odor. Although research has been hindered by the requirement of subjective odor measurements, the limitation of analytical techniques, and the limited understanding of the diesel combustion process, significant progress has been made in diesel odor research which has already led to the reduction of diesel odor emissions.