The preceding chapters in this section have dealt with several aspects of serum and urine protein analysis for immunoglobulins. Overwhelmingly, the single most important reason for performing these studies is to detect monoclonal gammopathies. This chapter briefly summarizes the various plasma cell proliferative diseases and then describes the use of the electrophoretic and nephelometric assays for the diagnosis, prognosis, and monitoring of monoclonal gammopathies. There are some general strategies for all laboratories as well as specific tests that are needed, depending on the disease presentation.