In normal healty individuals, the plasma cells produce numerous immunoglobulins each with its own unique protein sequence and hence a unique mass. When examined together, the distribution of the masses forms a Gaussian distribution. Patients whom have plasma cells that overproduce immunoglobulins (M-proteins) are at risk for developing serious diseases such as multiple myeloma. Currently, patients suspected for such diseases are screen by protein electrophoresis. Our invention relates to the use of the unique molecular mass of the light chain portion of the immunoglobulin to detect these monoclonal proteins. In short, after concentrating serum for immunoglobulins, the light chains are disassociated from the heavy chain by reductions and denaturing. The mass distribution of the light chains is then analyzed using LC-TOF mass spectroscopy. Patients who have a M-Protein are identified by observing light chain masses which are over represented in the distribution of light chains.