Clinical trials with hematopoietic growth factors (granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, interleukin-3, and erythropoietin) have been performed in patients with myelodysplastic syndromes. Absolute neutrophil counts can be readily raised to within the normal range by treatment with granulocyte colony-stimulating factor or granulocyte-macrophage colony-stimulating factor. Moderate increases in platelet counts have been reported for approximately 20% of patients during treatment with interleukin-3. Treatment with high-dose erythropoietin leads to an increase in hematocrit or decrease in transfusion needs in 15% to 20% of patients, but an improved response rate of approximately 40% has been reported for the combined treatment of erythropoietin with either granulocyte colony-stimulating factor or granulocyte-macrophage colony-stimulating factor. Although meta-analyses of published phase I/II trials allow a rough estimation of response rates and an improved selection of patients who are most likely to respond, phase III trials have not yet been published.