It was studied experimentally whether excess iron excretion can cause anemia in growing rats given desferrioxamine (DFO) intramusclarly. In the group injected with 150 mg/kg DFO daily for five weeks, urinary iron excretion started to increase after one week, and then hemoglobin concentration decreased after two weeks of treatment. The difference in hemoglobin concentration between the experimental and control groups was significant when treatment was continued for four weeks, although no significant differences were observed in erythrocyte counts. Thus, hypochromic anemia was induced. However, DFO at this dose did not retard growth in rats. In the second step, iron metabolism was examined. The same dose of DFO was administered to another group of rats every day for the same period. Compared to the control group, serum iron levels were higher in the rats injected with DFO. On the contrary, there were no differences in the total iron binding capacity. Liver nonhemin iron content in DFO-injected rats showed a marked decrease, which was nearly half of that in the controls. Diminution of bone marrow sideroblasts and bone marrow stainable iron was found at almost every case treated with DFO. It was demonstrated in these experiments that excess iron excretion induced by DFO resulted in iron deficiency anemia. These results give an experimental support to the concept of "Iron-losing anemia", anemia caused by the loss of nonhemin iron.