The goat anti-rabbit Ig antibodies are prepared by hyperimmunizing animals in a manner that produces high affinity antibodies. These are then purified by an affinity chromatography procedure designed to remove any low affinity antibodies which may be present. Cross-reactivities that are likely to interfere with specific labeling are removed by solid-phase adsorption techniques. The final product is then subjected to rigorous quality control assays including immunodiffusion, solid-phase enzyme immunoassays, gel electrophoresis and solid-phase binding assays. In preparing the labeled antibodies, great care is taken to ensure the maximum degree of labeling with no alteration in the specificity and affinity of the antibody. The labeled antibody then undergoes a further series of quality control assays, including immunohistochemical analysis.