A new human cell line, SP-49, was established from the peripheral blood of a patient with leukemic conversion of diffuse lymphoma, medium-sized cell type. SP-49 cells were shown to have intracytoplasmic and surface immunoglobulin and Leu-12 antigen, but were negative for Epstein-Barr virus nuclear antigen. Chromosome analysis demonstrated that SP-49 had t(11;14) chromosome translocation involving 11q13 and 14q32, where oncogene bcl-1 and immunoglobulin heavy chain gene, respectively, were reportedly located.