Disinfecting water with chlorine dioxide eliminates trihalomethane formation but generates several contaminants of its own. Government regulation under consideration would require the removal of these by-products to levels for which no detection methods have existed. Chemists at Miami University of Ohio have developed a method to measure chlorate, chlorite, and hypochlorite ions at levels of less than 1 mg/L. For analyses of mixtures that have several chlorinecontaining oxidizing agents other than chlorate ion, the modified iodometric method and a modification of the Suzuki-Gordon method can be applied. The detection accuracy range is plus or minus three percent. Includes 23 references, tables.