Several immunological procedures can be successfully carried out using nonpurified antibodies, such as unfractionated antisera or ascitic fluid/culture supernatant containing monoclonal antibodies (MAbs). However, a much “cleaner” result can often be obtained if some form of enrichment or isolation of immunoglobulin (Ig) is employed. Some procedures, such as conjugation with isotopes, fluorochromes, or enzymes, and preparation of immunoaffinity columns cannot usually be efficiently performed with nonpurified immunoglobulin; other procedures may yield artifactual results if whole antiserum or ascitic fluid is used as a source of antibody. Purification of immunoglobulin is therefore at least useful and sometimes essential for a range of immunological methods. This process may consist of purification of total IgG or subpopulations (e.g., subclasses) of IgG from antisera/ascitic fluid/culture supernatant or the isolation of a particular antigen-binding fraction of Ig from such fluids. The former can be achieved by biochemical procedures, whereas the latter usually requires some type of affinity purification.