The success of one of the writers (1) in developing an efficient pediculicide against lice suggested the possibility of there being also substances that would at least repel other insects, particularly mosquitoes. Real warfare against such insect pests should, of course, be waged in their breeding places, and their propagation prevented. During the many years, however, that will elapse before the extermination of mosquitoes, our comfort, as well as freedom from mosquito-borne disease, will be greatly enhanced by any not unpleasant substance that will keep them at a distance. Various substances have long been used as culicides or culicifuges. Among them may be mentioned various essential oils, such as those of citronella, cedar, lavendar, tar, eucalyptus, pennyroyal, peppermint, cassia, and turpentine. Also recommended have been camphor, castor oil, iodoform, menthol, nutmeg, musk, leeks, crushed pepper, naphthalin, lemon juice, vinegar, kerosene, tobacco smoke, punk smoke, and other fumes and smudges.