The present invention relates to the diagnosis of hematopoietic disorders and to determining the prognosis of patients affected by such disorders. The methods generally comprise determining a level of myeloperoxidase in a body fluid sample from the individual and using the level as a factor for diagnosing the disorder in the mammal or as a factor for determining the prognosis of a patient diagnosed with such a disorder. Myelodysplastic syndrome, acute myeloid leukemia and chronic myeloid leukemia are exemplary disorders. Also provided are method of cancer therapy involving reducing the level of myeloperoxidase in the body fluid of the individual.