Granulocyte colony stimulating factors (G-CSF) has a wide spectrum of action: it stimulates proliferation and differentiation of granulocyte-macrophage progenitors, it promotes the chemotactic activity of monocytes and granulocytes and it develops the antibody-dependent cytotoxicity of neutrophils. In vivo G-CSF induces leucocytosis and it hastens the granulocyte recovery after chemio-radiotherapy. So it has been used in many pathologies: aplastic anaemia, AIDS in treatment with antiviral drugs, myelodysplastic syndromes, acute leukemias and solid tumors. If G-CSF is administered after chemotherapy, both in acute leukemias and in solid tumors, it reduces the duration of neutropenia and the number of febrile episodes so that it is possible to give the whole therapy at the planned dosage with no delay. However G-CSF does not modify the incidence of complete remissions and the overall survival. G-CSF allowed the increase of dose-intensity in chemoresistent neoplasms even if this therapy is always complicated by a heavy extrahaematological toxicity. Moreover G-CSF shortens the total duration of neutropenia after autologous or allogenic bone marrow and peripheral stem cell transplantation even if the appearance of the first neutrophil is not accelerated.