A concise assessment of the risks to human health and the environment posed by exposure to 1 2-dichloroethane, an industrial chemical mainly used in the synthesis of vinyl chloride. The compound is also used in the manufacture of various chlorinated solvents, as a fumigant, and in the manufacture of anti-knock additives for gasoline. The document is the first in a new series aimed at the characterization of hazards and dose-response for exposures to selected industrial chemicals. With this goal in mind, documents in the series focus on studies and findings considered critical for risk characterization. A review of findings from studies in laboratory animals and limited epidemiological studies in humans supports the conclusion that 1 2-dichloroethane is a probable human carcinogen, and that exposure should be reduced as much as possible. Using the results of gavage studies in experimental animals, the carcinogenic potency, expressed as the dose associated with a 5% increase in tumor incidence, was calculated to be 6.2-34 mg/kg body weight per day. As humans are exposed primarily via the inhalation route, guidance values for air of 3.6-20 micrograms/m3 or 0.36-2.0 micrograms/m3 were derived, calculated on the basis of a margin of 5 000-fold or 50 000-fold less than the estimated carcinogenic potential. This margin of 5 000 to 50 000 affords protection similar to that associated with the range for low-dose risk estimates generally considered to be essentially negligible. The report notes, however, that the calculation, based on the results of gavage studies, probably overestimates the risks of human exposure as 1 2-dichloroethane is less potent when inhaled.