Developed by the U. S. Army following its experience with jungle warfare during World War II, N,N-Diethyl-meta-toluamide (DEET) was originally tested as an agricultural pesticide. It was placed into military service as a repellent in 1946 and entered the civilian market in 1957. DEET remains the most common active ingredient in insect repellents. Strangely enough, the mechanism by which DEET repels insects has been debated for over 50 years. Recent evidence indicates that the substance repels pests by scrambling the insect odor code.