Acrylonitrile is a colorless, highly flammable liquid with a characteristic unpleasant, irritating odor. Manufacture in the U.S. is based on a reaction between propylene, ammonia, and air; and its primary use is in the production of acrylic and modacrylic fibers such as Acrilan, Orlon, and Courtelle. Acrylonitrile is toxic when inhaled, ingested, or absorbed through intact skin. It is a severe skin and eye irritant. Its high toxicity is due to the liberation of free cyanide in the body, which inhibits enzymes responsible for cellular respiration. The occupational standard for an 8-hour time weighted average is 20 ppm, based on animal studies and human data on hydrogen cyanide exposure. The primary emission sources in descending order are production, end product manufacture, and bulk storage. Emissions from manufacture occur mainly from the main process absorber vent, which is uncontrolled at most U.S. plants. Four control devices are, however, available: CO-boiler, thermal incinerator, incinerator plus steam generation, and a flare system. Based on the results of the health effects research presented in this report, and the ambient concentration estimates, it appears that acrylonitrile as an air pollutant does not pose a threat to the health of the general population.