We show that transplantation of bone marrow retrovirally transduced with MLL-CBP induces myeloid leukemias in mice that are preceded by a long preleukemic phase similar to the myelodysplastic syndrome (MDS) seen in many t(11;16) patients but unusual for other MLL translocations.     ///    This suggests that the leukemic effect of MLL-CBP results from the fusion of the chromatin association and modifying activities of CBP with the DNA binding activities of MLL.. 