Colony-stimulating factors (CSFs) are glycoprotein growth factors that influence the proliferation and differentiation of hematopoietic progenitor cells. Among CFSs granulocyte colony-stimulating factor (G-CSF) is thought to be major stimulator of production of human neutrophilic granulocyte. G-CSF have recently moved from the basic research to the clinical use and have been suggested to have important roles in cancer management. Today two kinds of recombinant G-CSF which have similar specific activity are commercially available, one is derived from ovarian cells of Chinese hamster and the other from E. coli. (Variant type of E. coli is now in trial.) Difference of these two is whether carbohydrate chain primarily seen in molecule of natural form is contained or not. In this report recombinant product of G-CSF for the clinical use is introduced. Preclinical study with recombinant G-CSF have suggested that it would stimulate granulocyte production in cancer patients with myelosuppression due to chemotherapy. Thus, after evaluation of toxicities and possible efficacy recombinant G-CSF has been introduced into phase II trial for the prevention of chemotherapy-induced neutropenia in various cancers. In this setting 2 micrograms/kg of subcutaneous administration for 14 days after aggressive chemotherapy was suggested to be optimal and to be acceptable for toxicities including bone pain or headache. In conclusion recombinant G-CSF is thought to be very useful drug for reduction of nadir of cancer chemotherapy-induced neutropenia and shortening of period of neutropenia.