Chlorobenzene (MCB), C6H5Cl, is a colourless, volatile, water-insoluble, flammable liquid with a penetrating smell of almonds. Chlorobenzene belongs to the family of organic halogen compounds, which is a large class of natural and synthetic chemicals that contain one or more halogens (fluorine, chlorine, bromine, or iodine) combined with carbon and other elements. Chlorobenzene has been made from the chlorination of benzene since 1868. It has been manufactured industrially since the early 20 C. In the past, cholorobenzene was used to make phenol and DDT. Today, it is still used to produce pesticidesandchemicals used to prevent or kill unwanted pests. Chlorobenzene is also used as a high-boiling solvent in the manufacture of adhesives, paints, paint removers, polishes, dyes, and drugs. Human exposure to chlorobenzene appears to be primarily occupational. In urban areas, chlorobenzene may be released to the ambient air during its manufacture and use. Chronic exposure of humans to chlorobenzene affects the CNS. Signs of neurotoxicity include numbness,cyanosis, hyperesthesia (increased sensation), and muscle spasms. Headaches and irritation of the mucosa of the upper respiratory tract and eyes have also been reported in humans chronically exposed via inhalation. The CNS, liver, and kidneys have been affected in animals chronically exposed to chlorobenzene byinhalation. Chronic ingestion of chlorobenzene has resulted in damage to the kidneys and liver in animals. EPA has calculated a provisional Reference Concentration (RfC) of 0.02 milligrams per cubic meter (mg/m3) for chlorobenzene based on kidney and liver effects in rats. The Reference Dose (RfD) for chlorobenzene is 0.02 milligrams per kilogram body weight per day(mg/kg/d) based on histopathologic changes in the liver in dogs. EPA has medium confidence in the study on which the RfD was based because it provided both a no-observed-adverse-effect level (NOAEL) and a lowest-observed-adverse-effect level (LOAEL) andincorporated several biochemical and biological endpoints; medium confidence in the database becauseseveral subchronic, chronic, developmental, and reproductive toxicity studies provide supportive data, butthey did not give a complete assessment of toxicity; and, consequently, medium confidence in the RfD.