For many biochemical applications including immunohistology, not only highly specific antibodies are of great importance, the degree of purity with respect to the bulk of contaminating proteins in sera is also a matter of concern. Conjugation of antibodies with enzyme molecules will always need highly purified antibodies, in other cases such as in indirect immuno-stainings (in which the primary antibodies are not labeled) an immunoglobulin fraction of the hyperimmune serum containing the primary antibodies will be sufficient. The choice of the purification method will depend on the type of application. When labeled primary antibodies are to be used in direct immuno-staining techniques, then antibody preparations with a high degree of purity are essential in order to obtain reliable conjugates with which to achieve clear-cut stainings with lowest possible background.