A mathematical model of iron kinetics derived by POLLYCOVE and MORTIMER (1961) was successfully used on normal adult rats. R.B.C. iron turnover number, mean delay of iron in red marrow for haemoglobinization, and the R.B.C. life span were determined. Comp < /strong>lete iron exchange between the main plasma iron pool, and the storage compart ments was detected. The findings elucidated the comp < /strong>lex equilibrium between the plasma iron and the various iron pools, namely the erythrocytic pool, itself com prising almost equal labile and fixed compartments and the storage pool. The equil ibrium shows that the iron actually deposited in the storage pool is little (97 Pg Fe/day) comp aired to the erythrocytic iron turnover (410 Pg Fe/day).