Iodo-trihalomethanes (I-THMs) are byproducts of the oxidative treatment ofiodide-containing drinking waters. These compounds, especially iodoform, are undesired becausethey can be responsible for taste and odor problems in drinking water. Naturally occurring precursors of I-THMs are iodide and natural organic matter (NOM). Several oxidants/disinfectants (ozone, chlorine, chloramine) oxidize iodide in a fast reaction to hypoiodous acid (HOI). Subsequently, HOI can react with NOM to form I-THMs. Alternative sinks for HOI are its oxidation to iodate or its disproportionation, which leads to iodide and iodate. From a competitive kinetics approach, we can conclude that the risk of the formation of I-THMs increases in the order of ozone<chlorine<chloramine. Includes 12 references, figures.