The purpose of this paper is to direct attention to the possibilites of sodium fluoride as an insecticide. Recent investigations of this salt as a stomach poison, which I have undertaken with cutworms and locusts, as well as its few but successful previously known uses as an insecticide against fowl-lice, Mallophaga on mammals, cockroaches, and earwings, indicates that sodium fluoride may, in a number of cases, replace the use of arsenical poisons. During the past decade the use of arsencial insecticides has increased rapidly. We are at present threatened with higher prices and possibly with a shortage of arsenic, a situation accentuated by the present cotton-boll weevil programme of the United States of America, which involves the use of tremendous quantities of arsenicals. Any cheap stomach poison effective against insects and promising as a substitute for arsenicals should therefore be of considerable interest to the entomologist and to the farmer, especially if it carries the additional advantage of being considerably less poisonous to man, stock and birds. Sodium fluoride meets these requirements.