Purity >95% as determined by SDS-PAGE. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is hematopoietic growth factor produced by endothelial cells, monocytes, fibroblasts, and T cells. GM-CSF stimulates the production of neutrophilic granulocytes, macrophages, and mixed granulocyte-macrophage colonies from bone marrow cells. GM-CSF promotes immune system development and regulates neutrophil function during infection. Human and mouse GM-CSF show no cross-reactivity.