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Abstract. The intestinal 59Fe absorption from ferri‐ and ferro‐haemogIobin‐59Fe and 59Fe3+ and 59Fe+ was calculated from whole body‐59Fe‐retention measurements in subjects with normal and depleted iron stores. A ferri‐haemoglobin‐59Fe/ferro‐haemoglobin‐59Fe absorption ratio of 1.03 ±0.11 was observed for the absorption of ferri‐haemoglobin‐59Fe (8.6± 0.77%) and ferro‐haemogIobin‐59Fe (8.7±0.94%) in persons with normal iron stores. Depletion of iron stores caused a slight but significant higher rise of ferri‐haemoglobin‐59Fe absorption (22 ± 1.7%) than the increase of ferro‐haemoglobin‐59Fe absorption (18 ±0.9%) so that the absorption ratio was 1.24±0.073.—This remarkable iron valence independence of haemoglobin iron absorption is in considerable contrast to the well‐established valence dependence of inorganic iron absorption which favours ferrous iron absorption especially with rising iron doses. The 59Fe3+/59Fe2+ absorption ratio for a diagnostic 0.56 mg Fe dose increased from 0.43 in subjects with normal iron stores to 0.74 in persons with depleted iron stores, whereas this absorption ratio was augmented only from 0.21 to 0.28 for the therapeutic 50 mg Fe‐dose.—The different influence of iron valence on iron absorption from inorganic and haemoglobin iron supports other evidence for the existence of two separate mechanisms for ferrous iron and haem iron absorption in humans.

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