Protein A is a type I membrane protein produced by several strains of Staphylococcus aureus. It has high-affinity binding sites for IgGs obtained from various species such as human, rabbit, mouse, and bovine. Protein A supported by agarose resin is prepared using a covalent coupling method and can be applied to the purification of IgGs. By using Protein A Agarose (Product No. P2461), human IgGs can be eluted under milder conditions (such as at pH 4.0) compared to using other resins with conventional eluting protocols.