We used the flow cytometric immunoassay to study the correlation between the rumor-suppressor gene product p53- and the DNA ploidy in 30 de novo cases of acute nonlymphocytic leukemia (ANLL). The results showed that 15 cases were positive expression for p53. As compared with p53 negative (p53) cases, the patients with positive p53 (p53+) had higher percentage of bone marrow blasts and lower peripheral leukocyte and platelet counts, which had no influence on the complete remission rate. Before treatment, DNA diploidy was seen in 18 cases including 12 p53- cases, and DNA aneuploidy in 12 cases including 9 p53+. After therapy, aneuploidy could be transformed into diploidy. Patients with P53+ or having aneuploidy in complete remission were at risk for early relapse. We believe that p53 may be involved in the process of leukemogenesis and progression of ANLL.