Samples ofHarpalus pennsylvanicusDeGeer,Pterostichus chalcitesSay, andScarites substriatusHaldeman taken from Iowa cornfields were analyzed for chlorinated hydrocarbon insecticide residues. Results are reported in ng of insecticide/g of beetle (ppb). The principal residues occurring in these field-collected carabids were dieldrin andp,p′-DDE. Smaller quantities of aldrin,p,p'-DDT, heptachlor, heptachlor epoxide, and lindane were detected. Although from the same field,H. pennsylvanicusandS. substriatuscontained significantly (P=0.05) different levels of aldrin, dieldrin, andp,p′-DDE.P. chalcitescontained the highest level ofp,p′-DDE (913.5μg/g). No significant differences (P=0.05) were found in the amounts of insecticide residues present between male and female beetles.FemaleP. chalciteswere dosed topically with 2 μl of an acetone solution of dieldrin. Five concentrations were used, varying from 10–250 μg of dieldrin/beetle. Mortality counts were made 48 h after application of the insecticide. The computed LD50was 3357 μg of dieldrin/g of beetle (ppm). This far exceeded the residue levels of dieldrin reported herein. Clearly,P. chalciteshas an extremely high resistance to dieldrin.