Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hemopoetic growth factor that is a member of the four-helix bundle family of cytokines and growth factors. It regulates the proliferation and differentiation of granulocytes and cells of macrophage lineage from bone marrow progenitor cells, mediating these activities through binding to its receptor. Most studies examining the effects of GM-CSF on HIV-1 replication in primary monocytes and macrophages, and in related cell lines, have demonstrated augmentation of HIV-1 expression in vitro, although some reports have been at variance with these findings. These laboratory-based observations have been confirmed in limited clinical trials. This review outlines the details of these studies and considers mechanisms by which GM-CSF may exert its effects on cells of this lineage.