Strains of onion maggot (Hylemya antiqua (Meig.)) highly resistant to the chlorinated hydrocarbon insecticides appeared in certain areas of the Pacific Northwest. Furrow treatments, seed treatments, and multiple surface applications of chlorinated hydrocarbons were ineffective. Seed, soil and surface treatments with organic phosphates did not give economic control. Furrow treatments of Guthion, Diazinon, ethion, Trithion, V-C 13, and Bayer 21/199 gave excellent control. Furrow treatments with malathion, Dipterex, Perthane, Bayer 19639, Sevin, Thiodan, DDT, Kepone, Dow ET-57, and endrin were ineffective. Thimet gave good control as a furrow treatment, but was phytotoxic. Parathion applied in the furrow protected onions for several weeks, then declined rapidly.