The GDM-1 permanent cell line was established from the peripheral blood of a patient with a Philadelphia chromosome negative myeloproliferative disorder, after transformation to acute myelomonoblastic leukemia. The GDM-1 cells exhibited the same characteristics as those isolated from the peripheral blood of the patient prior to death: cells contained non-specific esterase sensitive to fluoride, myeloperoxidase, lysozyme (muramidase), and exhibited both Fc and complement (C 3) receptors but lacked B- and T-cell surface markers including T-associated antigens. E-rosetting capacity, surface and intracytoplasmic immunoglobulins and EBV determined nuclear antigen (EBNA). The GDM-1 cells bore the Ia receptor and the myeloid leukemia antigen (M-1). The karyotype of the cultured leukemic cells showed the same specific chromosomal abnormalities present in the monoblasts obtained from the peripheral blood prior to death, indicating that the cell line was derived from the original leukemic cells.