A 12-yr-old boy with acute leukemia was found to have paraproteinemia and Bence-Jones proteinuria. The paraprotein was characterized as immunoglobulin M, type κ and the Bence Jones protein as free κ-chains. Increased amounts of β2-microglobulin were found in the patient’s serum and urine. Electron microscopic and immunofluorescence studies provided evidence of the presence of lymphoid leukemia cells apparently responsible for the production of the paraprotein.

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