Hepatic iron uptake from transferrin has been studied in 7 patients with treated hemochromatosis. When compared with a control group with similar serum iron and transferrin saturation the hemochromatotics had a significantly higher 4-hr iron uptake value. Uptake in the precirrhotic and cirrhotic hemochromatotics was not significantly different, suggesting the existence of a cellular abnormality of hepatic iron metabolism in this disease. The results provide an explanation for the development of siderosis in some patients with idiopathic hemochromatosis and a normal serum iron concentration.