The role of myeloid growth factors, such as granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor, in the management of acute myeloid and acute lymphoblastic leukemias has been evaluated extensively in multiple clinical trials. Growth factors have been given before, concurrently, or sequentially with chemotherapy with the goal of reducing the duration of neutropenia and consequently the incidence and severity of infections, and improving the rate of remissions and overall survival. They also have been studied as chemotherapy-sensitizing agents in an effort to recruit dormant myeloid stem cells into the sensitive phase of the cycle. Additionally, growth factors, shown to stimulate proliferation and differentiation of leukemia cells in vitro, were evaluated as monotherapy in patients with acute leukemia. Most studies show modest improvement in the duration of the neutropenia, which does not consistently correlate with the severity of infection, rate or duration of remissions, or disease-free and overall survival. Attempts to enhance the chemosensitivity of the leukemic cells and decrease drug resistance failed to improve the rate of remission and survival in several large series. However, more recent reports suggested an improved outcome in younger patients with acute myeloid leukemia with normal karyotype. Several anecdotal case reports have shown that growth factor monotherapy can induce a complete remission in patients with acute leukemia. Data from the published clinical trials do not seem to support emergence of drug-resistant leukemia, worsening toxicity, and bone marrow failure with growth factor administration.