A novel ferritin type specifically targeted to mitochondria has been recently found in human and mouse. It is structurally and functionally similar to the cytosolic ferritins, well-characterized molecules found in most living systems which are designed to store and detoxify cellular iron. Cytosolic ferritins in mammals are ubiquitous while mitochondrial ferritin expression is restricted mainly to the testis, neuronal cells and islets of Langherans. In addition, it is abundant in the iron-loaded mitochondria of erythroblasts of patients with sideroblastic anaemia. The characterization of recombinant and transfected mitochondrial ferritin indicated that this protein has a role in protecting mitochondria from iron-induced damage. These data suggest that it is an interesting tool to study the iron metabolism in this organelle. In addition, it may be useful for the diagnosis of myelodysplastic syndromes and in protecting mitochondria from the toxic effects of excess iron.