A new human plasmacytoma cell line (Karpas 707) has been established from a myeloma patient. The cultured cells are negative for Epstein-Barr viral nuclear antigen and free of mycoplasma. They are similar to plasma cells and secrete only lambda light chains. The cells are hypodiploid and contain the Philadelphia chromosome and other abnormalities. This cell line may be suitable for the production of human monoclonal antibodies.