Iron deficiency is an important cause of anemia in patients with chronic kidney disease (CKD), but intravenous iron is infrequently used among patients who are not on dialysis.Ferumoxytol is a novel intravenous iron product that can be administered as a rapid injection.This Phase Ⅲ trial randomly assigned 304 patients with CKD in a 3∶1 ratio to two 510-mg doses of intravenous ferumoxytol within 5 ±3 d or 200 mg of elemental oral iron daily for 21 d.The increase in hemoglobin at day 35, the primary efficacy end point, was 0.82 ± 1.24 g/dl with ferumoxytol and 0.16 ± 1.02 g/dl with oral iron (P <0.0001).Among patients who were not receiving erythropoiesis-stimulating agents, hemoglobin increased 0.62 ± 1.02 g/dl with ferumoxytol and 0.13 ± 0.93 g/dl with oral iron.Among patients who were receiving erythropoiesis-stimulating agents, hemoglobin increased 1.16 ± 1.49 g/dl with ferumoxytol and 0.19 ± 1.14 g/dl with oral iron.Treatment-related adverse events occurred in 10.6% of patients who were treated with ferumoxytol and 24.0% of those who were treated with oral iron; none was serious.In summary, a regimen of two doses of 510 mg of intravenous ferumoxytol administered rapidly within 5 ± 3 d was well tolerated and had the intended therapeutic effect.This regimen may offer a new, efficient option to treat iron deficiency anemia in patients with CKD.