The electrochemical behaviour of the herbicides metamitron and isometiozine has been studied by adsorptive stripping voltammetry for electro-adsorptive potentials of −350 mV and −500 mV, respectively, with Britton-Robinson buffer solution and adjusting the ionic strength to 0.25 mol/l in NaClO4. The high sensitivity of this technique allows the quantification of the two studied herbicides with detection limits of 3.0×10−10 mol/l for metamitron and 1.0×10−9 mol/l for isometiozine at reduction potentials of −450 mV and −560 mV, respectively. A method for their determination in soils is proposed, involving previous extraction in Cl2CH2 which allows determination of 0.44 ng/g soil for metamitron and 0.97 ng/g soil for isometiozine.