Numerous oral iron preparations are available for the treatment of iron deficiency anemia but only very few studies have been designed to measure the bioavailability of iron preparations. The aim of this assay is to determine the bioavailability of iron formulated as natural ferric protein (TM/FMOA)(FMOA=Ferrimannitol ovalbumin) and natural ferric protein with folic acid (TM/FMOA+FOL) in healthy and anemic rats. Determination of the bioavailability of iron has been carried out by studying the serum level-time curves after i.v. administration of a single dose of 1 mg iron/kg in the form of ferrous sulfate, and after oral administration of 2 mg of iron/kg in the form of TM/FMOA or TM/FMOA+FOL. The Cmax values obtained after oral administration of TM/FMOA and TM/FMOA+FOL are greater in the case of anemic rats, while the tmax values are similar in both types of animals. The bioavailability (F) is greater for the anemic rats (80% approx), and the presence of folic acid does not appear to influence the bioavailability of the iron. This bioavailability data with TM/FMOA can predict good results in further experiments in human beings with iron deficiencies.