Leukemic cells from an 8-year-old girl with ANLL-M2 expressed precursor B-cell antigen CD19, but none of the myeloid antigens CD11b, CD13, CD14 and CD33. After culture, the cells expressed CD11b and CD13. The cells carried a high number of granulocyte colony-stimulating factor (G-CSF) receptors. In chromosome analysis, metaphase cells were obtained only in the case of culture with G-CSF. The karyotype was a variant of t(8;21)(q22;q22). Southern blot analysis revealed rearrangement of the AMLI gene located on chromosome 21. These observations may suggest that even without myeloid surface antigens and with precursor B-cell antigen, ANLL-M2 with t(8;21)(q22;q22) has apparent myeloid characteristics.