By using the technique of recoil-free absorption (Mossbauer effect) in iron, the authors found large amounts of iron, yielding a well-defined spectrum different from that of oxy- or deoxyhemoglobin, in whole erythrocytes of 13 patients with β-thalassemia major and intermedia, 3 with hemoglobin H disease, 2 with sickle-cell anemia, and 1 with unstable hemoglobin Hammersmith. The Mossbauer spectra at various temperatures of this additional component of iron were found to be identical to spectra obtained from isolated ferritin or hemosiderin. This observation, together with additional arguments, strongly suggests that the compound responsible for the additional subspectrum is an iron storage protein, ferritin or hemosiderin. The amounts of ferritin-like iron were comparable to those of hemoglobin iron and were particularly large in reticulocytes. No ferritin-like iron was detected in patients with severe autoimmune hemolytic anemia and pernicious anemia. The large quantities of ferritin-like iron in hemoglobinopathies are probably due to intracellular hemoglobin denaturation and the consequent release of excess iron.