SummaryIron is necessary for cellular oxydation processes; bound with a protoporphyrin it enters into the composition of cytochromes and hemoglobin molecule.Human body contains about 4 g iron most of which being in hemoglobin.Iron is stored as ferritin and to a lesser degree as hemosiderin in the liver, the spleen and bone marrow.In plasma it is linked with a beta-globulin : transferrin or siderophilin.Normal male looses daily about 1 mg iron through urines and stools. This excretion is not related to the magnitude of storage. Thus normal iron requirement is 1 mg per day. When iron deperdition increases, iron need rises : for instance, in hemorrhages (menstruation, chronic digestive bleedings), pregnancy and lactation. Therefore females need 2 or 3 times more iron than males.Our daily iron intake is comprised between 10 and 15 mg of which about 10 % are absorbed. In stomach, iron is separated from protein complexes and is rapidly reduced in the ferrous form. Maximal absorption occurs in the duodenum, decreasing along the small intestine.The regulation mechanism of iron absorption is not fully understood. Clinical and experimental data show that iron absorption increases in iron deficiency or when erythropoiesis is exaggerated. Inversely, iron absorption is depressed when iron stores are large or erythropoiesis reduced. It is assumed that iron balance is regulated by intestinal absorption.About 1 /1oo of hemoglobin iron (25 mg) is liberated each day since red cells survival time is 100 days. This iron is taken up by marrow erythroblasts for hemoglobin synthesis. Iron plasma level is regulated by the equilibrium between these two processes.Ferrokinetic measurements are briefly described.