The pollution of the environment with Kepone(R) (decachlorooctahydro-1,3,4-metheno-2H-cyclobutal(cd)pentalen-2-one) by an industrial manufacturer of the pesticide resulted in the contamination of several terrestrial media, including biological life, near the entry of the insecticide into the ecosystem. The substrate investigated and for which residue methodology was developed included river sediment, soil, water, shellfish, and finfish. Rigorous extraction techniques using the Soxhlet apparatus and the Polytron(R) tissue homogenizer were required for complete removal of Kepone from the samples. Finfish tissue was the most difficult to analyze. For this type of substratum, a preliminary cleanup by gel permeation chromatography was required to remove most of the lipid material followed by a micro Florisil(R) column elution to eliminate polychlorinated biphenyls (PCBs). Cleanup of shellfish and other environmental samples was accomplished with a micro Florisil column only. Electron capture gas chromatography was used to analyze the sample extracts. Recoveries of Kepone from fortified samples averaged 84% or greater.