Background/Aims: Storage iron turnover has remained poorly understood since 1953. In addition, errors in measurements of the storage iron turnover rate (SIT) by ferrokinetics have been detected and the causes of those errors need to be elucidated. Methods: A new, computer-assisted method, “serum ferritin kinetics,” was introduced for the quantitation of ferritin iron and hemosiderin iron. Ferrokinetics and non-ferrokinetic methods were used to determine the body iron turnover rate. Results and Conclusion: Using serum ferritin kinetics, patients with normal iron stores and iron overload were found to have 2 iron pathways between ferritin and hemosiderin: recovery of ferritin taking iron from hemosiderin in iron mobilization and iron transformation from ferritin to hemosiderin in iron deposition. In addition, underestimation of the SIT by ferrokinetics was confirmed by comparing SIT by ferrokinetics with the standard SIT as the sum of SIT of 3 major iron-storing cells. This underestimation was caused by extra radio-iron fixation to red cells. Ferrokinetics does not give the actual body iron turnover due to the behavioral difference between radio-iron and pre-existing body iron. Recent findings on ferritin and hemosiderin iron turnover will be a potential tool for the diagnosis and therapy of hematological disorders.