The relationship between the level of erythropoiesis and iron balance was evaluated in 13 subjects with idiopathic refractory anemias. Serum ferritin levels and bone marrow iron stores were increased only in those patients with ring sideroblasts, erythroid hyperplasia and ineffective erythropoiesis. The magnitude of the increase correlated with the duration of anemia and the degree of increase in the erythron iron turnover. Ferritin levels were not related to the severity of the anemia, indicating that increased iron stores did not represent a shift of iron from the erythron or an absorption response to anemia per se. It does suggest that the level of erythroid proliferation directly affects gastrointestinal iron absorption, which in time leads to iron overload.