The hemopoietic growth factors are peptide hormones that are known to be responsible for the in vitro and in vivo proliferation of bone marrow progenitor cells into mature differentiated cells. These cytokines have had a major impact on the management of patients with cytopenias and have been extensively used as an adjunct to the management of patients with hematologic malignancies, with or without prior intensive chemotherapy. Other potential uses, being rigorously studied, include the potential mobilization of stem cells as well as recruitment phase-specific cells into the cell cycle, thus providing a more sensitive environment for targeting specific chemotherapeutic agents.