The study of proteinuria, and especially the search for Bence Jones proteins (BJP), has almost always required urine concentration. We evaluated a high-sensitivity electrophoretic method using unconcentrated urine based on colloidal gold staining. The sensitivity for the detection of BJP is further enhanced by immunofixation. Sensitivity to BJP is better than 1 mg/L and, apart from the alpha-1 microglobulin, all the proteins relevant to the classification of proteinuria can be visualized with a sensitivity of approximatively 3 mg/L.