An analytical method which, permits the determination of the chlorotriazine herbicides Atrazine, Cyanazine and Simazine, their dealkylated degradation products Deethylatrazine and Deisopropylatrazine and the organophosphorus pesticides Fenitrothion and Tetrachlorvinphos in soil samples in the ppb range (0.5–100 ng/g) is described. Two clean up procedures involving Florisil column chromatography and gel permeation chromatography with Bio-Beads SX-3 packing material have been compared for reducing the interferences from the soil matrix. The recoveries varied from 75 to 103±16% depending on the compound, and clean up method. Analysis have been carried out by gas chromatography with nitrogen/phosphorus detection and liquid chromatography with diode array detection. Advantages and limitations of both techniques are discussed. Gas chromatography-mass spectrometry in the electron impact mode and thermospray liquid chromatography-mass spectrometry in the positive ion mode have been employed as confirmatory characterization techniques. The methodology has been validated by analyzing residue levels of Atrazine, Deethylatrazine and Fenitrothion in real soil samples which varied from 0.02ng/g up to 10μg/g, depending on the period of application and pesticide use.