Benzene is mostly used in the production of organic chemicals such as styrene, polystyrene, various styrene copolymers, latexes and resins, phenol, cyclohexane, aniline, alkylbenzenes (used in detergents), and chlorobenzenes. Benzene is an intermediate in the production of anthraquinone, hydroquinone, benzene hexachloride, cyclohexane, benzene sulfonic acid, and other products used in drugs, dyes, insecticides, nylon monomers, and plastics. Benzene occurs naturally in crude oil and gasoline and is added to unleaded gasoline for its ability to increase octane and anti-knock. The concentration of benzene in these fuels is typically 1–2% by volume. Therefore, employees in workplaces exposed to exhaust gases from motor vehicles are highly exposed to benzene. In the USA, potential exposure to benzene occurred in agriculture, during oil and gas extraction, construction, production of food products, tobacco, textiles, lumber and wood, printing and publishing, exposure to oil and coal products, rubber production, leather production, and transport and health services. In the People’s Republic of China industries with the highest reported exposure are leather, electronic devices, machinery, footwear, office supplies, and sports equipment. Benzene causes acute myeloid leukemia/acute nonlymphocytic leukemia, and positive associations between benzene exposure and acute lymphocytic leukemia, chronic lymphocytic leukemia, multiple myeloma, and non-Hodgkin’s leukemia have been observed. Urinary trans, trans-muconic acid (t,t-MA), and S-phenylmercapturic acid (S-FMA) are sensitive markers for recent low-level benzene exposure.