1. Results of studies of gastrointestinal absorption of ferrous iron in normal children and those with heterozygous thalassemia were similar.
2. In one patient with absent erythropoiesis but severe anemia, no increase in the amount of iron absorbed was noted.
3. In sickle cell-hemoglobin C disease and hereditary spherocytosis having only slight anemia in the presence of increased erythropoiesis, normal amounts of iron were absorbed.
4. Patients with sickle cell anemia and thalassemia major in whom there was active erythropoiesis and marked anemia absorbed abnormally large amounts of iron. The amount absorbed by individuals with the latter disease could be reduced by administration of transfusions and concomitant suppression of erythropoiesis.
5. Usual values for serum iron and latent iron-binding capacity in several congenital hemolytic syndromes have been presented and their significance discussed.
6. No specific effect on absorption was noted by increased or reduced amounts of tissue or serum iron or by reduced or increased latent iron-binding protein.