The growing complexity of modern industry brings increasingly larger problems for medicine in the identification and prevention of new industrial diseases. With the development of modern refrigeration, there has sprung up in a short time a huge new industry for the manufacture of refrigeration machines. Various substances are used as refrigerants, the most common and oldest being ammonia, sulphur dioxide and recently methyl chloride. Methyl chloride, while used extensively in the chemical industries and as a local anesthetic, has received little or no attention in the literature of industrial hygiene, and even toxicologists have failed to consider it of sufficient importance to require more than passing notice. Since this substance has come into more general use as the cooling medium in refrigerators, its toxicological importance demands attention. LITERATURE In a survey of the literature one finds few references concerning the toxicity of methyl chloride. When this substance is mentioned it