The iron-chelating agent, deferoxamine, was studied in 16 patients with thalassemia major. Urinary excretion of iron in response to 0.75 gm of deferoxamine, intramuscularly, ranged from 2.2 to 44.8 mg Fe/24 hours. In response to a subcutaneous infusion of 1.5 gm deferoxamine for 18 hours, iron excretion increased by an average of 240%. The intravenous infusion of large doses of deferoxamine for 18 hours resulted in the highest rate of iron excretion, as much as 447.5 mg Fe/24 hours in response to 16 gm of deferoxamine. Administration of vitamin C increased chelation-induced excretion of iron in most patients more than five years of age. Preliminary evidence suggests that further iron accumulation can be prevented and excessive iron stores can be depleted by the intramuscular, subcutaneous, or intravenous administration of deferoxamine.