Extracts of the soils made with a mixture of benzene and isopropanol are clarified with activated charcoal. The extracts are placed on filter paper in petri dishes, and the reaction of the insects to the residue of each test sample is compared with the reactions to known residues of the toxicant. From this comparison the amount of toxicant is estimated and expressed as lbs. per 3-inch acre. When both materials are present, the chlordane is assayed and then removed by wetting and drying the filter papers before assaying the DDT residues. Possibly the most practical procedure would be to determine the total organic chloride chemically and the chlordane biologically and to calculate the DDT from the organic chloride in excess of that in the chlordane.