A protein that can be found in the urine of people with certain forms of protein disorders, such as amyloidosis and multiple myeloma. In most cases of multiple myeloma, only one type of excess intact (whole) immunoglobulin is produced. In a minority of cases, only a section of an immunoglobulin called “free light chain” is produced in large quantities. These excess free light chains are released into the bloodstream, and since they are relatively small molecules, they are filtered by the kidneys and released into the urine. Another term for this excess free light chain in urine is Bence Jones protein.