Divalent metal transporter I (DMT1) is expressed by duodenal enterocytes and thought to be involved in transport of iron across the apical cell membrane of the villus duodenal cells. To determine its role in hereditary hemochromatosis (HH) a common genetic disorder of iron metabolism, we used ß₂-microglobulin knockout (ß₂m-/-) mice, a mouse that accumulates iron similar to that observed in HH. The ß₂m-/- and control C57BL/6 (ß₂m+/+) mice were fed control, iron loaded or iron deficient diets. For all diet types the hepatic iron levels were greater for ß₂m-/- than ß₂m+/+ mice, with an increase and decrease in hepatic iron levels when the mice were fed iron loaded and iron deficient diets, respectively. Increasing the iron availability increased plasma iron levels in both ß₂m+/+ and ß₂m-/- mice. By contrast, reducing the iron availability decreased the plasma iron concentration in the ß₂m+/+ mice but had no effect on the plasma iron concentration in ß₂m-/- mice. DMT1 was not detectable in mice fed the normal or iron-loaded diets using immunohistochemistry. In Western blots, however, the protein was consistently observed in ß₂m+/+ and ß₂m-/- mice irrespective of the dietary regime. DMT1 expression was increased to the same extent in ß₂m+/+ and ß₂m-/- mice in response to feeding an iron-poor diet. In both strains of mice fed the iron-poor diet, DMT1 was evenly distributed in the differentiated enterocytes from the base to the tip of the villi but was absent from the crypts of Lieberkuhn. The fact that DMT1 expression was induced to a similar degree in genetically normal mice and ß₂m-/- mice when they were fed the iron-poor diet suggests that the observed effects were due to the state of iron deficiency in the mucosal cells rather than being directly due to the genetic defect.