Chlorine dioxide (ClO2), chlorite (ClO2(-1)), and chlorate (ClO3(-1)) in drinking water decreased blood glutathione and RBC osmotic fragility in vivo. The osmotic fragility and glutathione content were also studied in rat blood treated with ClO2, ClO2(-1), ClO3(-1) in vitro. RBC hemolysis was decreased in rat blood after 30, 60, and 120 minutes by all treatments. The glutathione content expressed as percentage of controls was decreased with incubation time. When ClO2 was added with reduced glutathione (GSH) to the blood, no effect on hemolysis was observed compared to control or to GSH alone at 2 hours, but decreased hemolysis was observed with ClO2 treatment alone. Addition of NADPH alone prevented ClO2 and ClO2(-1) and ClO3(-1) from exhibiting hemolysis resistance, while glutathione reductase (GR) and its cofactor (NADPH) increased hemolysis about 1.5-2 fold. Removing GR only resulted in increased resistance to hemolysis with ClO2 or ClO2(-1). The formation of disulfide bonds between sulfhydryl groups in erythrocytic membranes and hemoglobin, causing precipitation of hemoglobin (yielding apparent resistance to hemolysis) can account for the difference between the hemolysis before and after the addition of GR.