The purpose of the Level I materials balance for chlorobenzenes is to evaluate the sources of release of the various chlorinated benzenes to the environment. The major route of commercial production of chlorinated benzenes is the direct chlorination of benzene with chlorine. Chlorinated benzenes are indirectly produced through the metabolism of pesticides, their production by marsh grass and their production as a byproduct of organic chemical production processes. Chlorinated benzenes are used consumptively in the production of many organic chemicals. These include chloronitrobenzene, diphenyl oxide, DDT, 3,4-dichloroaniline, 2,5-dichlorophenol, pentachloronitrobenzene, rubber intermediates, dyes, pesticides, and aromatic fluorocarbons. In addition, chlorinated benzenes have many nonconsumptive uses, including use as a solvent, pesticide, deodorizer, dielectric fluid, coolant, lubricant, heat transfer medium, and synthetic transformer oil. The major sources of release of chlorinated benzenes to the environment appear to be from their various non-consumptive uses. Releases from production and consumptive uses appear to be comparatively minor.