The isolation procedure combines ammonium sulfate fractionation, anion exchange chromatography, preparative zone electrophoresis, and gel filtration. The method is suitable for the isolation and purification of the group-specific components. The Gc proteins representing the gene products of the two common homozygous Gc-types) Gc 1-1 and Gc 2-2, have been prepared. Gc belongs to the group of ₂-globulins of relatively low molecular weight (4.1S, molecular weight 50,800) and relatively low carbohydrate content (3.3 per cent). The total amino acid composition of the two homozygous group-specific components is very similar; treatment with reducing agents and alkylation provides no evidence for the presence of more than a single polypeptide chain in the Gc molecule.