A method of treating acute myeloid leukemia (AML), including the steps of (i) measuring a density of blast cells in the peripheral blood and the bone marrow of a subject with AML; (ii) administering to the subject a CXCR4 antagonist; and (iii) administering to the subject a therapeutically effective amount of the CXCR4 antagonist and a therapeutically effective amount of a chemotherapeutic agent, if the blast cell density in the peripheral blood is less than 10% of the total peripheral white blood cells, or at least five-fold lower than the blast cell density in the bone marrow, or at least two-fold higher one day or more following step (ii).