Two Bence-Jones proteins, one of kappa and the other of lambda type, from the urine of two myeloma patients were identified by protein electrophoresis (PEP) and immunoelectrophoresis (IEP). Urine specimens were concentrated and dialyzed with Ultrafiltration. The concentrated products were passed through a Sephadex G-100 column, and the fractions of Bence-Jones proteins were recycled in diethylaminoethyl (DEAE) ion exchange chromatography. Purified Bence-Jones proteins were mixed thoroughly with complete Freund adjuvant and inoculated into rabbits. The monospecific antisera to kappa and lambda chains were obtained by absorption with Bence-Jones proteins of the opposite types.