A new hematopoietic cell line, designated KCL-22, was established in vitro by cultivation of pleural effusion cells obtained from a woman with chronic myelogenous leukemia in blast crisis. KCL-22 grew in suspension culture with a doubling time of 24 h and consisted of immature undifferentiated cells which were positive for periodic acid-Schiff and acid phosphatase staining. Chromosome analysis of the KCL-22 line showed a female karyotype with double Ph1 chromosomes and additional chromosome abnormalities. Its representative karyotype was 52,XX, + 1p-,+6,+8,+8,+8, t(9q+;22q-), +22q-. This cell line possessed receptors for the Fc portion of IgG, but lacked lymphoid cell characteristics and the Epstein-Barr virus-associated nuclear antigen. These results indicate that the KCL-22 cells were derived from chronic myelogenous leukemia cells. This cell line should prove useful for research involving various aspects of chronic myelogenous leukemia.