The underground mining industry recognizes that diesel-powered equipment has many advantages over its electric counterparts such as greater mobility, flexibility, and high power density, which result in increased productivity. There is, however, an attendant health risk for miners exposed to diesel exhaust. A miner working in an underground mine using diesel equipment is exposed to a wide array of pollutants from the diesel exhaust. These include carbon monoxide, carbon dioxide, nitric oxide, nitrogen dioxide, sulfur dioxide, diesel exhaust aerosol, and a variety of hydrocarbon compounds. Diesel exhaust aerosol consists mainly of carbonaceous soot, sulfates, trace metals, and adsorbed or condensed soluble organic compounds. A quantitative definition of the health risk resulting from these exposures remains elusive, but during the past several years progress has been made in defining the problem.