Diesel fuel and the products of its combustion represent one of the toxins most commonly encountered by people living in both urban and rural areas of the world. As nations become more heavily populated, there will be increasing reliance on diesel fuel to power mass transportation and commercial vehicles, as well as heavy machinery involved in construction, farming, and mining. The majority of patients who present to urban primary care clinics and emergency departments will have had significant chronic exposure to diesel exhaust because most use and/or live near busy streets and highways.