The effect of Hfe (haemochromatosis) gene deletion on the hypoxic response of iron absorption was investigated. Hfe knock-out mice were exposed to 0.5 atmospheres hypoxia for 3 d before in vivo iron absorption was measured. Both wild-type and Hfe knock-out mice had similar (two- to threefold) increases in iron absorption in response to hypoxia. We conclude that the Hfe gene product is not required for mice to increase iron absorption rates in response to hypoxia. The data further support the hypothesis that at least two independent mechanisms for the regulation of iron absorption exist, only one of which requires Hfe.