Protein G Resin is an affinity chromatography medium designed for easy, one-step purification of classes, subclasses and fragments of immunoglobulins from biological fluids and from cell culture media. The recombinant protein G ligand is coupled to 4% highly cross-linked agarose. The static binding capacity of Protein G Resin is greater than 20 mg goat IgG/ml settled resin. The dynamic binding capacity will vary depending on several factors such as target antibody, flow rate etc. Table 1 lists the characteristics of Protein G Resin. Protein G, a bacterial cell wall protein isolated from group G Streptococci, binds to mammalian IgGs mainly through Fc regions. Native protein G has 3 IgG binding domains and also sites for albumin and cell-surface binding. The latter have been eliminated from recombinant protein G to reduce nonspecific binding. Although protein G has very similar tertiary structures to protein A, their amino acid compositions differ significantly, resulting in different binding characteristics. Protein G can be used for purification of mammalian monoclonal and polyclonal IgGs from biological fluids and cell culture media.