1. Absorption of inorganic iron was studied in thirty-four patients with chronic renal failure by a double isotope technique.
2. Eight patients with normal iron balance had a mean absorption of 3·5%, ten patients with iron overload had a mean absorption of 3·6%, and sixteen patients with iron depletion had a mean absorption of 58%. Thus, alterations in absorption appeared to be related to disturbances in iron balance.
3. The rate of erythropoiesis had no evident effect on iron absorption nor did the degree of anaemia.
4. The presence of renal disease and the degree of azotaemia likewise did not appear to affect absorption.