Protein G Magnetic Beads are an affinity matrix for the small-scale isolation and purification of immunoglobulins. A truncated form of recombinant Protein G is covalently coupled to a nonporous superparamagnetic particle. Protein G exhibits high affinity for subclasses of IgG from many species including human, rabbit, mouse, rat and sheep (1). In addition, Protein G can be used for immunoprecipitations with mouse monoclonal antibodies (1). The protein is coupled through a linkage that is stable and leak resistant over a wide pH range. This permits the immunomagnetic purification of IgGs from ascites, serum or cell culture supernatants; the matrix can then be regenerated without loss of binding capacity. Protein G Magnetic Beads can be used to immunoprecipitate target proteins from crude cell lysates using selected primary antibody. In addition, specific antibodies can be chemically cross-linked to the Protein G coated surface to create a reusable immunoprecipitation bead, avoiding the co-elution of antibody with target antigen (2,3).