DDT is extremely toxic to certain insects, but precise information concerning its mode of action is lacking. Histological studies have failed to show any significant morphological changes following exposure. Hence, it is likely that the insecticide acts on metabolic processes of the insect, producing modifications which eventually lead to its death. To determine whether such modifications occur, normal insects and others poisoned with various concentrations of DDT were compared with respect to weight, rate of desiccation over anhydrous CaCl2, and the content of water, glycogen, glucose, fat, and protein. This information may assist in understanding the action of the compound and may eventually lead to the production of more effective insecticides and methods of insect control.