A method is described for handling and testing the susceptibility of larvae of the cabbage maggot, Hylemya brassicae (Bouché), to insecticides, and data are given on the tolerance of susceptible and resistant strains to various insecticides. Larvae of the onion maggot, H. antiqua (Meigen), also could be handled and tested in the same manner. The cabbage maggot was tested by 4 other methods, with all applications made to the adult fly, namely topical application, spray tower, impregnated paper, and treated food pads. The results obtained with dieldrin-resistant strains of H. brassicae are compared with those for the normal susceptible strains.