Near-tetraploid chromosomes were observed in a patient with acute myeloblastic leukemia with maturation (M2 in FAB classification). Large and morphologically bizarre leukemic cells and giant neutrophils in each maturation stage were observed in both peripheral blood and bone marrow. Cytogenetic studies revealed that the main stem line was 93; XXYY, +9, and DNA cytofluorometry showed that these large leukemic cells and giant neutrophils had 4C DNA content. These findings strongly suggested that these giant neutrophils were derived from leukemic clone with tetraploidy.