Studies about the chemical reactivity of compounds widely used in the environment are needed. The chemical reactivity of triazines toward oxidants was tested in the laboratory with cerium(IV) ammonium nitrate and ozone. Simazine, atrazine and terbutylazine were tested. The oxidative N-dealkylation occurred both with cerium ammonium nitrate and with ozone at acidic pH. The N-de-ethylation was invariably preferred to the N-dealkylation reaction. A degradation pathway for triazine herbicides is suggested. The kinetics of the oxidation of these triazines with ozone at pH 3 and the kinetics of the saturation of the solution with ozone have been evaluated. These data may be useful for the prediction of the persistency of these compounds in the environment.