Protein L protein binds immunoglobulin (Ig) light chains in a wide range of species including human mouse rat pig hamster and chicken but has low affinity for Igs from guinea pig and rabbit. This bacterial protein interacts with Ig light chains without blocking the antigen binding site of the Igs . Thus protein L can be used for the detection of IgG IgM IgA IgE and IgD containingº light chains. It may also be used to detect fab and scfv fragments containingº light chains. Protein L does not bind to bovine sheep or goat Igs. Hence when bound to a solid support (sepharose) protein L may be used to directly purify monoclonal antibodies from media supplemented with BSA or fCS and also to directly purify human or mouse antibodies from goat bovine or sheep proteins. rProtein L is a recombinant form of the native protein and contains two Ig binding protein L fragments.