The chlorination of water supplies accomplishes, in addition to the destruction of microorganisms, a number of other objectives. The reaction of chlorine with compounds such as phenol may result in the production of undesirable taste and odor compounds. If the chlorination is carefully controlled, however, even the latter can be improved. In any case, as a result of chlorination, one of the most commonly performed chemical determinations is the measurement of free available or combined available chlorine in water. At present, there are nine methods for the determination of free and combined chlorine. Unfortunately, none of these have been studied collaboratively. This study was undertaken in an effort to evaluate and prehaps eliminate some of them.