Human granulocyte colony-stimulating factor (G-CSF), a 20 KD glycoprotein consisting of 174 amino acids, is one of the physiological regulators mainly produced by endothelial cells, monocytes-macrophages and fibroblasts, under various stimulations such as infections. The molecule specifically and markedly stimulates the production of neutrophils associated with an expansion of the hematopoietic stem cells/progenitor cells and elevates the functional activities of neutrophils. Under favor of the unique biological activities, recombinant human G-CSF (rhG-CSF) has now become an epoch-making agent for the purposes of reduction of bacterial/fungal infections, particularly in neutropenias of various causes, increased dose intensity of chemotherapeutic drugs in cancers, and solving various problems in hematopoietic stem cell transplantation.