Autoantibodies developing in humans contribute to the pathogenesis of several diseases, and injected therapeutic antibodies can also trigger adverse side effects. An efficient and rapid elimination of these antibodies are therefore critically needed. Antibody removal by plasmapheresis and immunoadsorption are commonly used methods but have their own limitations. Bacterial enzymes that can cleave IgG molecules or remove carbohydrate moieties to ameliorate their immunogenicity or effector functions in vivo offer new avenues for drug development. Recent discoveries highlight the possibility of cleaving or modifying IgG in vivo by injection of enzymes. Such an approach opens up new therapeutic possibilities not only for the control of pathogenic antibody-mediated inflammatory diseases but also allograft rejection or the treatment of side-effects of 'biologicals' such as monoclonal antibodies.