Since deferoxamine B, when administered as a single daily intramuscular injection of 0.75 g, is unable to promote sufficient urinary iron excretion to achieve net negative iron balance in siderosis, we evaluated its administration as a constant infusion over 24 hours. We compared intravenous and subcutaneous routes in 24 siderotic patients who had excreted 420 to 630 mg (mean, 480 mg) of iron per month on intramuscular therapy. With the intravenous route urinary iron excretions increased to 570 to 3690 mg (mean, 1595 mg) per month. Constant subcutaneous delivery was 90 per cent as effective as intravenous administration on a dose-for-dose basis. Noteworthy net cumulative urinary iron excretions (urinary iron excretions minus transfused iron), often in excess of 1 g per month, have been maintained in all patients. Constant subcutaneous deferoxamine administration may prove to be an effective and practical means of eliminating large quantities of iron in siderosis.