A powerful cleanup procedure for determination of chlorinated pesticides and polychlorinated biphenyls (PCBs) in difficult agricultural matrixes like feeds or crops was developed to eliminate the interferences in chromatograms obtained by gas chromatography with electron capture detection. The adsorption material used was ENVI-Carb, a graphitized nonporous carbon material. This procedure proved to be more reliable than the established cleanup procedure, which uses gel permeation chromatography and silica gel cartridges. Because ENVI-Carb cleanup delivers clear, colorless eluates with no interferences, chlorinated pesticides and PCBs may be detected at levels as low as 0.0004 mg/kg for monitoring purposes. Accuracy was validated through a series of recovery experiments.