Abstract: Monoclonal protein (M protein) is a serum surrogate used to conduct diagnostic, prognostic, and therapeutic evaluations of monoclonal plasma cell proliferative disorders. Two basic methods, namely, serum protein electrophoresis and immunofixation elec-trophoresis, are employed to detect and characterize M protein. Although these techniques have considerably improved, M protein quantification exhibits several drawbacks. In serum protein electrophoresis, M protein can migrate to various locations, and low M pro-tein levels cannot form a typical peak; as a consequence, additional problems in measurements arise. In2009, a novel immunoassay in-volving a heavy/light chain (HLC) was developed. HLC recognizes immunoglobulins with specific heavy and light chain isotypes. The ratio between an involved monoclonal immunoglobulin and an uninvolved background polyclonal immunoglobulin can be calculated through immunoglobulin quantitation by using isotype-specific light chains.Thisreviewsummarizesrelevantparametersthatprovide diagnostic, prognostic, and therapeutic data regarding monoclonal plasma cell proliferative disorders.