Various haematological, ferrokinetic and iron absorption measurements were carried out on 15 patients with chronic renal failure who were undergoing regular haemodialysis. There was no evidence that the rate of iron absorption was impaired significantly by the depressed erythropoietic activity present in these patients. In contrast, there was a significant inverse correlation between the rate of iron absorption and the serum ferritin concentration, which has been shown to be an index of the size of the iron stores. This relationship, which was shown with both small (3 mg) and large (50 mg) doses of ferrous iron, was no different from that previously noted in subjects with normal renal function. These results suggest that iron deficiency in patients with chronic renal failure undergoing regular haemodialysis can be adequately prevented or treated with oral iron therapy, since the absorptive mechanism for iron appears to be normal.