A 53-year-old woman presented to the orthopedic department with severe diffuse muscular and bone pain. An x-ray of her right upper extremity revealed a lytic destructive lesion in the right humerus. Computed tomography scans showed multiple lytic lesions in the spine and pelvis, and a biopsy confirmed the presence of 70% plasma cells, which were κ light chain restricted. The patient was referred to a hematologist. Although no monoclonal protein was detected in the serum by protein electrophoresis or by immunofixation electrophoresis (IFE),1 the κ free light chain (FLC) was increased at 47.2 mg/L (reference interval, 3.3–19.4 mg/L), with a κ/λ FLC ratio of 23 (reference interval, 0.26–1.65). Serum concentrations of β2-microglobulin and albumin were 248 nmol/L (reference interval, 59.5–153 nmol/L) and 37 g/L (reference interval, 34–47 g/L), respectively. The urine protein concentration was not increased, but protein electrophoresis revealed a small M (monoclonal) spike in the γ region (32 mg/24 h). In addition, IFE identified a monoclonal κ light chain (Bence Jones protein). On the basis of these findings, the patient was informed that she had stage I (International Staging System) oligosecretory/nonsecretory multiple myeloma (MM).