Brace® 10G (a.i. isazofos), an organophosphorus insecticide being tested for potential registration for control of various corn pests, was applied to 14 Iowa cornfields in an 18-cm band at planting at 0.73 kg a.i. per hectare. Effects of isazofos on wildlife were evaluated by searching treated fields and adjacent areas for carcasses and monitoring survival of radiomarked northern bob-white and ground-foraging passerines. Fifty carcasses (26 birds, 21 mammals, three herps) were recovered following application. Four of the bird and 12 of the mammal carcasses found postapplication had tissues suitable for residue analysis but did not contain detectable isazofos residues. Brain cho-linesterase (ChE) activities measured in four bird and seven small mammal carcasses were not depressed in relation to reference values. Two radiomarked bobwhite died before application, and two radiomarked bobwhite and three radiomarked passerines died following applications. Three of these birds had sufficient tissues for residue analysis, but none had detectable isazofos residues or brain ChE depression relative to reference values, and pre- and postapplication mortality rates of radio-marked birds were not significantly different.