Our results show that direct inhibition of Fes kinase activity by a selective pyrazolopyrimidine compound (WZ4-49-1) resulted in growth suppression in three separate Flt3-ITD+ AML cell lines as well as human TF-1 myeloid cells transformed by retroviral transduction of Flt3-ITD. The gene discussed is FLT3; the disease is acute myeloid leukemia.