Haemochromatosis is a common, inherited disorder of iron metabolism. The gene (HFE), which is mutated in the majority of patients, has been cloned. The HFE protein, however, is not an iron transporter, but rather is thought to function as a regulator of iron absorption. The cloning of theHFE gene was followed rapidly by the identification of further proteins involved in the iron absorption pathway in the duodenum and transfer to the main iron storage site in the liver. The identification of a new metal ion transporter in the rat provided the first molecular information on the active absorption of metal ions by mammalian cells.1 This divalent metal transporter 1 (DMT1) has a broad substrate specificity that includes Fe²⁺ and a range of other divalent metal cations.1 (DMT1 is also referred to as divalent cation transporter 1, DCT1, and natural resistance-associated macrophage protein 2, Nramp2.) DMT1 mRNA is widely expressed, with high levels in the proximal duodenum, the site of absorption of iron and most other divalent metal ions.1 The biological importance of this transporter is shown by its involvement in two naturally occurring animal mutants of iron metabolism. Homozygous mutation ofDMT1 …