Monochloroacetone was introduced in 1914 as a war gas, and presently it has a number of uses as a chemical intermediate. Apart from its biological properties as a lacrimator and vesicant, it is not a well-studied compound toxicologically. A series of acute toxicity studies were done using different routes of administration. An Ames mutagenicity test also was performed. These data were compared to manufacturing use information and data published in the literature. It is recommended that direct contact with liquid and vapor be prevented through strict engineering controls and that air concentrations be kept below 1 ppm as a ceiling concentration.