A two-step screening of urine samples for Bence-Jones proteins is described. The proposed method is fast and fully mechanized; quantitative results are obtained within minutes. As a first step alpha 1-microglobulin, albumin, transferrin and IgG are measured immunonephelometrically. Then the cumulative concentration of the four markers is compared with that of total protein, which is determined by nephelometry during trichloroacetic acid protein precipitation. Bence-Jones proteinuria is indicated by large concentrational differences (greater than 31%) between the four markers and total protein. As a second step, Bence-Jones proteins are assessed directly if they are present. Immunoglobulin light-chains are measured immunonephelometrically and the kappa:lambda ratio is used to discriminate between monoclonal and polyclonal forms. Using this strategy, urine samples from 84 patients with monoclonal gammopathia or multiple myeloma were screened. Bence-Jones proteinuria was detected in 40 cases. In a reference collective (69 patients with different types of renal proteinuria) Bence-Jones proteinuria was not observed. Comparing the results with those obtained by immunofixation, the nephelometric method has a sensitivity of 100% and a specificity of 97%, differing only in a single false-positive result. Additional information about renal forms of proteinuria is supplied by the first screening step. This permits an assessment of the renal involvement in Bence-Jones proteinuria, and the method can also be used for nephrological diagnosis.