Fenton- and modified Fenton systems such as H₂O₂/HOONO/Fe²⁺ have been studied for oxidative degradation of 1,4-dioxane, morpholine, cyclohexanone and bentazone. Both ferrous sulfate (FeSO₄.7 H₂O) and Mohr´s salt (NH₄)₂Fe(SO₄)₂.6 H₂O have been used as Fe²⁺ ion sources. With Mohr´s salt the Fenton reaction was successfully carried out under both acid (pH 3) and neutral (pH 7) conditions. The degradation ability of the new Fenton-like system H₂O₂/HOONO/Fe²⁺ has also been tested. The main results of this study are the use of Mohr´s salt under neutral conditions and practical utilization of the H₂O₂/HOONO/Fe²⁺ system in the Fenton reaction. Some mechanistic aspects of the degradation initiated by H-atom abstraction with HO ^. radical are also discussed.