Previous work suggested that during the catabolism of haemoglobin a physico-chemical form of iron was released which was more readily chelatable by desferrioxamine than normal storage forms, as ferritin-haemosiderin. Desferrioxamine chelation was therefore investigated in five patients with major fractures in which haemoglobin catabolism is greatly enhanced by the red cell destruction which proceeds in the associated haematoma. Considerable increases in the amounts of iron mobilized by desferrioxamine were observed from the second day after injury. In severe interstitial haemorrhage, these values tended to increase until 10 to 20 days, and sometimes were as high as chelation values seen in haemochromatosis. These results are considered to support the hypothesis that a highly chelatable form of iron is found at some stage during haemoglobin catabolism.