Four leukemia cell lines; NALM-20, established at the onset of leukemia and NALM-21, -22 and -23 established at the relapse of the disease were found to be t(9;22)-positive leukemia lines having the biphenotypic feature of B cell and myeloid cell characteristics. In addition, a polyclonal Epstein-Barr virus-transformed normal B cell line, B250, was established from the peripheral blood at the onset of the disease.