1. Ferritin has been partially purified from the serum of patients with idiopathic haemochromatosis.
2. Incubation with neuraminidase of this partially purified serum ferritin eliminated much of the microheterogeneity of the protein so that only ferritin of isoelectric point approximately 5·8 was present.
3. There was no change in the total amount of ferritin present (measured immunologically) or in the percentage of ferritin binding to concanavalin A.
4. Incubation of liver, spleen or heart ferritin with neuraminidase did not change the isoelectric focusing patterns.