Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a glycoprotein necessary for the growth, differentiation, and function of cells of the granulocyte-macrophage lineage. This agent has been molecularly cloned and expressed in bacteria, yeast, and mammalian cell lines, providing a limitless source of the pure human protein for use in children. Here, we briefly review the discovery, biologic characterization, gene identification and cloning, and clinical experience to date with this new agent, focusing where possible on the use of recombinant GM-CSF in children.