The potential of immunoglobulin-free light chain detection and measurement in biological fluids, and particularly in urine, has not yet been fully explored in clinical medicine, because of differences in sensitivity and lack of standardization of both quantitative assays and qualitative analysis. The ability to identify monoclonal free light chain, i.e., Bence-Jones protein, reliably in urine is of great clinical interest even when it occurs only in such small amounts that they frequently remain undetected by the routine methods used in many laboratories. The standardized adoption of both qualitative and quantitative procedures with comparable sensitivity is suggested to allow precise characterization of the clonal nature, and therefore the clinical role, of any free light chain excess.