This paper describes the results of a public opinion survey on testing of diesel exhaust odors conducted during 1969 and 1970. Major goals of the research were to relate public opinion of the odors and the objectionability associated with them to odor intensity, and to obtain a dose-response curve as the primary result. The dose-response curve was needed to assess odor-control technology by providing a criterion for deciding whether or not the effect of a given control item would be noticed by the general public, reduce complaints, or be worth the cost and effort required for its implementation.The engine used as the live odor source for the subject research was a two-stroke cycle type similar to those used in many buses. This engine type was chosen because its exposure to the public in urban bus applications is very widespread, and because a large portion of the Environmental Protection Agency's odor research had been performed with similar engines.It was found that a relationship existed between perceived diesel exhaust odor intensity and the objectionability of these odors. The nature of this relationship was that increasingly intense diesel exhaust odors were considered increasingly objectionable. The data also show that a substantial reduction in diesel exhaust odor intensity would be required to cause a worthwhile reduction in the objectionability of these odors.