Human Granulocyte Macrophage Colony Stimulating Factor (hGM-CSF), a hematopoietic growth factor, is mainly involved in granulopoiesis and monocytopoiesis. It is produced by T-cells and macrophages in response to antigens, and by endothelial cells and fibroblasts following induction of variouscytokines [1]. A monomeric protein of 127 amino acidswith six glycosylation sites and two intra disulfide bonds[2,3], glycosylated and non-glycosylated hGM-CSFs show similar biological activities[4]. Other than its connection to the growth and development of granulocytes and macrophages, it is also indispensable for the proliferation of erythroid and megakaryocytic cells[5].Recombinant Human Granulocyte Macrophage Colony Stimulating Factor (rhGM-CSF) produced in P. pastoris a glycosylated polypeptide. A fully biologically active molecule, rhGM-CSF has a molecular mass of 26-32kDa analyzed by SDS-PAGE and is obtained by proprietary refolding and chromatographic techniques at GenScript.