Two of the most commonly used chlorinating agents for water disinfection, hypochlorite and chloramines, were employed to investigate the degradation of clethodim in conditions simulating tap water treatment. The main clethodim degradation products were identified by using liquid chromatography (LC) coupled with mass spectrometry (MS). The main degradation process was oxidation to sulfoxide and then to sulfone. Degradation half-life was calculated for both parent clethodim and the first degradation product, clethodim sulfoxide. Whereas some other different minor by-products were identified when the degradation occurs with either sodium hypochlorite or chloramines, no other chlorinated by-products were found under the conditions tested. © 2005 Friedr. Vieweg & Sohn/GWV Fachverlage GmbH.