Beyond its role in hemoglobin synthesis, iron plays an important part in host defense mechanisms. Sequestration of iron is a mechanism to control bacterial proliferation and virulence. However, uremia results in several immunologic deficits, including impaired lymphocyte mitogenic response and granulocyte function abnormalities such as impaired phagocytosis, respiratory burst, and myeloperoxidase activity. At the other end of the spectrum, iron overload can impair immune function and stimulate bacterial growth and virulence. Overtreatment with iron increases the preexisting risk of infectious complications for uremic patients, as indicated by hyperferritinemia in hemodialysis patients who have impaired polymorphonuclear leukocyte (PMNL)-induced bacterial killing. These results suggest that maintaining iron status within normal range is important to control potential increased risk of infection in patients with end-stage renal disease (ESRD).