Unexplained acute hemolytic anemia is sometimes seen in uremic patients undergoing hemodialysis. Chloramines, which are oxidant compounds made up of chlorine and ammonia and are widely used as bactericidal agents in urban water supplies, have been found responsible for two recent epidemics, in dialyzed uremic patients, of acute hemolytic anemia characterized by Heinz bodies. Chloramines produce denaturation of hemoglobin, both by their direct oxidizing capacity and their ability to inhibit red cell reductive (hexose monophosphate shunt) metabolism.