Iron deficiency is a frequent complication in chronically hemodialyzed patients because of the significant blood losses associated with this technique. Quantitating iron stores (by marrow examination or serum iron and total iron-binding capacity) on a repetitive basis had been difficult or unreliable, often resulting in failure to recognize iron deficiency superimposed on the existing anemia of chronic renal failure, or overtreating, which can lead to iron excess. Use of the serum ferritin allows easier quantitation of iron stores and, when measured serially in dialysis patients, can predict the emergence of iron deficiency. There was no correlation between serum ferritin levels and serum iron, total iron-binding capacity, or percent transferrin saturation. Iron absorption studies show that food iron absorption is physiologic, increasing when the serum ferritin is below 30 ng/ml, decreasing when more than 300 ng/ml. Treatment of iron deficiency with oral iron compounds increases serum ferritin levels and usually can maintain iron balance.