Granulocyte-macrophage colony-stimulating factor (GM-CSF) is one of the four major colony-stimulating factors (CSFs) that regulate hematopoiesis. GM-CSF can stimulate a single bone marrow stem cell to proliferate and differentiate into mature neutrophils, eosinophils, granulocytes or macrophages. The outcome of recent clinical trials indicates that GM-CSF has the prospect of being clinically effective in augmenting the recovery of hematopoiesis in recipients of autologous bone marrow transplantation, in cancer patients suffering from the hematopoietic toxicity associated with chemotherapy and radiation therapy, and in patients with acquired immunodeficiency syndrome (AIDS).