For more than 150 years, the presence of Bence Jones protein [immunoglobulin free light chains (FLCs)] in the urine has been an important diagnostic marker for multiple myeloma. Indeed, it was the first cancer test, and 100 years before any others (1). Over the last few years, however, interest in FLCs has undergone a renaissance. Development of serum tests for free [kappa] and free [lambda] has opened the door to new applications and increased their clinical importance (2). By way of comparison, the management of diabetes mellitus was hugely improved when blood replaced urine for glucose analysis. The report by Katzmann et al. (3) in this issue of Clinical Chemistry adds valuable confirmatory data on serum FLC testing. It is the first report of the assays being used in routine clinics with analysis of results on 1020 samples. As the authors point out, the performance of the tests has matched up to the retrospective studies that have been published previously.