In this study we evaluated the effect of 1-year, subcutaneous desferrioxamine daily infusion on iron balance in 23 thalassemia major children, aged 8-74 months, with transfusional iron accumulation less than 3.8 g at the outset of the trial. Statistical analysis showed a significant correlation between transfusional iron accumulation and percentage of transfusional iron eliminated. Confidence limits analysis of these data indicated that over 3.5 g of transfusional iron load, 95% of the patients may achieve balance. The appropriate time to begin desferrioxamine infusion, therefore, seems to be after about 30 transfusions of packed red blood cells when iron accumulation of approximately 3 g is reached. As we found a statistically significant correlation between transfusional iron eliminated and serum ferritin levels, the evaluation of serum ferritin alone can also predict when balance can be obtained.