Big brown bats, Eptesicus fuscus, were fed single doses of varying amounts of DDT in corn oil injected into meal worms. All the doses of DDT fed to the bats, 40 milligrams or more per kilogram of body weight, were lethal. Within a few hours to 13 days after being dosed, the animals developed convulsions; some bats survived up to 3 days after the oniset of the symptoms of poisoning. Bats appear to be far more sensitive to DDT than any other mammal yet tested.