MRI is an optimal clinical (research) tool to provide information on brain morphology and pathology and to detect metal ions that possess intrinsic magnetic properties. Non-heme iron is abundantly present in the brain in three different forms: "low molecular weight" complexes, iron bound to "medium molecular weight complexes" metalloproteins such as transferrin, and "high molecular weight" complexes as ferritin and hemosiderin. The total amount and form of iron may differ in health and disease, and MRI can possibly quantify and monitor such changes. Ferritin-bound iron is the main storage form of iron and is present predominantly in the extrapyramidal nuclei where its amounts normally increase as a function of age. Ferritin is water soluble and shortens both, T1 and T2 relaxation, with as result a signal change on the MR images. Hemosiderin, a degradation product of ferritin, is water-insoluble with a stronger T2 shortening effect than ferritin. The larger cluster size of hemosiderin and its water-insolubility also explain a lack of significant T1-shortening effect on T1-weighted images. Using both in vitro specimens and intact brain tissue in vivo we demonstrate here that MRI may be able to distinguish between ferritin- and hemosiderin-bound iron.