Methods are provided for treating hematological disorders by inhibition of DNA hypomethylation and histone deacetylase. Such disorders include, for example, acute promyelocytic leukemia, acute lymphoblastic leukemia, chronic myelogenous leukemia, myelodysplastic syndromes, and sickle cell anemia. The methods comprise: administering to a patient suffering from the disease a therapeutically effective amount of a DNA methylation inhibitor such as a cysteine analog such as decitabine, in combination with an effective amount of histone deacetylase inhibitor such as hydroxamic acid, cyclic peptide, benzamide, butyrate, and depudecin.