Monoclonal gammopathies are characterized by serum monoclonal component (MC) plus an intact immunoglobulin and a free light chain (FLC), or a combination of both. The measurement of FLC with Freelite® is the standard practice recommended by International Myeloma Working Group guidelines. Recently, Hevylite® heavy/light chains (HLC) assays were introduced to specifically target junctional epitopes between the heavy and light chains of intact immunoglobulins, allowing the independent quantification of the involved (MC) and uninvolved (polyclonal immunoglobulin background) HLC isotype. Between January 2012 and March 2014, 90 patients were examined: 49 multiple myeloma (MM), 6 smoldering MM (SMM) and 35 monoclonal gammopathy of undetermined significance (MGUS). Of these 90 patients, 300 samples were collected at different times. The diagnostic and monitoring contribution of Hevylite A and G assays was assessed in all 90 patients examined. Additionally, 3 representative cases were selected. The Hevylite absolute values and ratio demonstrated high sensitivity and specificity with respect to serum protein electrophoresis and serum immunofixation. The combined use of Hevylite A and G with Freelite was particularly useful in dubious cases with more than one MC or with co-migrating components, as well as in the course of monitoring to assess the independent change of FLC and HLC, possibly reflecting the presence of clonal heterogeneity in the cohort. From this study, it can be concluded that FLC and HLC are independent, useful markers to monitor the MC and to assess with greater specificity and sensitivity the effect of therapy, thereby providing clinical support. Further studies are required to assess the prognostic potential of Hevylite in MGUS and SMM.