OBJECTIVE To review the current clinical uses, ongoing investigations, and future applications of hematopoietic growth factors. Approved cytokines, as well as cytokines not yet released for general use, are included in this review. RESULTS Clinical applications of granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), and erythropoietin, the three recombinant hematopoietic growth factors currently commercially available for clinical use in the United States, are discussed. Macrophage colony-stimulating factor (M-CSF), interleukin-3 (IL-3), PIXY321, stem-cell factor (SCF), IL-1, IL-6, and IL-11 represent cytokines not yet approved; the majority of these newer agents have their principal action at an earlier time point in the hematopoietic cascade than the currently approved cytokines. Current clinical uses of hematopoietic growth factors include decreasing cytopenias associated with chemotherapy, those due to congenital or acquired bone marrow failure states, those that occur after high-dose chemotherapy and bone marrow transplantation, peripheral-blood progenitor mobilization, and supportive care of leukemia patients. CONCLUSIONS Hematopoietic growth factors have made a significant impact on the prevention of infections associated with chemotherapy-induced neutropenia, shortening of neutropenia following high-dose chemotherapy and progenitor-cell transplantation, and chemotherapy-associated anemia. Cost-effectiveness and cost-benefit analyses in future phase III and pharmacologic studies will aid in the assessment of these agents.