1. Transferrin was isolated from umbilical cord blood by means of gel filtration on Sephadex G-150 and ion-exchange chromatography on DEAE-Sephadex A-50, and its properties were compared with those of transferrin isolated from human adult blood.
2. Both glycoproteins were able to bind a maximum of two atoms of iron per molecule and have very similar amino acid and carbohydrate compositions.
3. The molecular weight of cord-blood transferrin, assessed by equilibrium centrifugation, was 78 200, and its sedimentation velocity appeared to be 5.2S.
4. Cord-blood transferrin and adult blood transferrin were found to be immunochemically identical.
5. No differences could be detected between the transferrins in their capacities to deliver iron to immature erythrocytes derived from rat bone marrow, which indicates that the rapid transport of iron across the placenta cannot be explained by differences between foetal and maternal transferrin.