Chlorine dioxide is under consideration for use as a water disinfectant alternative to chlorination in the United States. A rising dose tolerance study was undertaken to assess the relative safety and tolerance of acute administration of chlorine dioxide and its byproducts, chlorite and chlorate, to normal healthy adult male volunteers. In evaluation of an extensive battery of laboratory tests and vital signs, no adverse physiological effects were identified. This provided a data base upon which a controlled 5-month study trial of these substances in normal healthy volunteer subjects was designed.