Transferrin was isolated and purified from bovine plasma. An intestinal segment in situ experiment showed that 19.2% of injected iron was absorbed when FeCl(3) (80 microg Fe/ml) was injected into a duodenum segment of iron-deficient rats. With addition of 10 and 20 mg of purified transferrin/ml, however, ratios of absorbed iron through duodenum segments were significantly increased to 52.7 and 57.9%, respectively. After transferrin-rich extract was isolated by batch type ion exchange chromatography, a soluble ferric complex of the transferrin extract was prepared by adding ferric salts to transferrin extract followed by dialysis, sterilization, and freeze drying. Results of the animal experiment for comparing bioavailabilities of different irons showed that irons in Fe-transferrin extract was most efficiently absorbed and incorporated into hemoglobin generation in anemic rats.