This paper gives some account and results of work conducted on the properties of ethylene oxide, as this compound has been recommended as an insecticide and vermin destroyer, and what is of more importance, as a fumigant for foodstuffs. The concentration recommended is in the nature of 2 lb. per 1000 c. ft. (or 1 part in 60) for 24 hours. It has also been mentioned as a possible agent for use as a lachrymator in war. The compound was examined by us as follows: On man. Inhalation of the vapour. Vapour effect on the skin. Fluid effect on the skin. On animals. The effect of splashes in the eye. Administration by intravenous injection. Administration by inhalation both in single and repeated exposures. Feeding with food contaminated by vapour and by spray. Estimation of the blood urea content in an animal given a fatal dose by intravenous injection.