To test the hypothesis that inhibition of Fes kinase activity may be of therapeutic value in AML, we first investigated the effects of Fes kinase inhibitors [16] from three distinct chemical classes (Fig 1) on the growth of AML cell lines either wild-type for Flt3 (THP-1) or expressing Flt3-ITD (MV4-11, MOLM-13 and MOLM-14). Here, FLT3 is linked to acute myeloid leukemia.