Cattle Feedlot Operations have always been famous for their odor. Owners and operators of feedlots usually become insensitive to the odor or feel that it is not objectionable. But neighbors, especially those downwind, very often do not share this feeling. Complaints which then arise are sometimes translated into legal action to force changes or removal of the feedlot. Reactions to odors are notoriously subjective. Perfumers and food dealers employ persons who are especially skilled in detecting and identifying odors, especially pleasant ones. But on objectionable odors there is far less information, so it was felt that an objective way to measure compounds which cause odors would be helpful in determining the true source of odors. Although the principal interest was in feedlots, other agricultural operations such as dairy farms and horse ranches have similar problems which might also benefit from a broad-base study of the odor problem.