Heart tissue from beta-thalassemia/hemoglobin E patients was taken at autopsy. The patients had received no blood transfusions or iron chelation therapy. Ferritin and hemosiderin were isolated from the tissue and studied using Fe-57 Mossbauer spectroscopy, transmission electron microscopy and electron diffraction. The ferritin was shown to contain mineral cores with a mean particle site of 7.37 (s.d. 0.84) nm. Electron diffraction and Mossbauer spectroscopy indicated that the cores had structures based on that of the mineral ferrihydrite and were superparamagnetic with a mean blocking temperature of 34 K on the Mossbauer measurement time scale. The hemosiderin particles ranged in size from 1 to 10 nm and were indicated to have a very poor crystalline structure. Mossbauer spectroscopic measurement indicated that the majority of the iron in the hemosiderin was paramagnetic/superparamagnetic at 4.2 K. Mossbauer spectroscopy of the heart tissue indicted that approximately 40% of the tissue iron is in the form of hemosiderin, 35% in the form of ferritin, 3% in the form of heme iron, and approximately 20% in the form of an unidentified form of iron that yields a spectral singlet with centre shift of 0.32 mm s(-1) at 15 K with respect to alpha-iron at room temperature. (C) 2000 Elsevier Science S.A. All rights reserved.