Background: Intestinal iron absorption is extremely high in neonatal mammals but falls rapidly to adult levels following weaning. The aim of this study was to investigate the molecular basis of this elevated neonatal absorption using the rat as an experimental model. Methods: RNA was extracted from various sections of the intestine of 10, 15, 20, 25 and 300 day old rats and the expression of the genes encoding DMT1 (Slc11a2), ferroportin (Slc40a1), Cybrd1 (Cybrd1) and hephaestin (heph) determined by ribonuclease protection assay. The hepatic expression of Hamp was studied at the same ages. Iron absorption was examined by following ⁵⁹Fe uptake in both whole animals and in isolated intestinal loops. Results: Slc11a2, Slc40a1 and Cybrd1 mRNAs were highly expressed in all regions of the small intestine and colon studied in suckling rats. However, after weaning, when iron absorption declined significantly, strong expression was retained only in the duodenum. No change in hephaestin mRNA occurred in any part of the digestive tract. In the distal small intestine and colon, Slc40a1 expression most closely followed the change in absorption that occurred after weaning. Hamp expression was low during the neonatal period and increased to adult levels following weaning. Conclusion: Our results suggest that the distal small intestine and colon contribute significantly to the high intestinal iron absorption seen in neonatal animals, and that this reflects increased expression of the iron transporters, particularly Slc40a1.