DDT was found to act on anopheline larvae as a nerve poison, disorganizing their movements so that they could not retain contact with the water surface. The toxic dose could be obtained either by contact or by ingestion. Because of the feeding habits of the larvae, a surface application is usually ingested. However, only a short exposure to DDT in oil soln. was toxic by contact. Death resulted from drowning even when sublethal dosages were given. Heart action in the posterior of the abdomen was always the last visible sign of life and often did not cease for more than 24 hrs. after the first tremors appeared.