Pesticides and their metabolites are extracted and concentrated from serum using C18 solid-phase extraction cartridges. The internal standard aldrin is added to 4 mL of serum or plasma, treated with 2 mL of methanol, and the resultant supernatant applied to the C18 cartridge. After several washes, pesticides are eluted from the column with isooctane and the eluate quantified with capillary gas chromatography using electron capture detection. Extraction efficiency is from 70 to 75% and the method detection limit ranges from 0.1–0.7 ng/mL depending on the analyte. Precision studies demonstrate that CVs range from 3.5 to 25.2%. Standard curves are linear to at least 7 ng/mL for lindane and chlordane isomers, heptachlor, heptachlor epoxide, oxychlordane, trans-nonachlor, dieldrin, dichlorodiphenyldichloroethylene (p,p′-DDE), dichlorodiphenyldichloroethane (p,p′-DDD), and dichlorodiphenyltrichloroethylene (p,p′-DDT).