Granulocyte colony-stimulating factor (G-CSF) is one of the latest products of molecular biology to permeate clinical practice. The results with this hematopoietic growth factor have been promising, and in one disease, congenital severe neutropenia, they have been exceptionally interesting. But questions have been raised about the safety of G-CSF in this rare disorder. To understand the clinical effects of G-CSF and the concern about its safety, it is important to know that the growth factor has multiple effects on cells of the granulocytic lineage. It not only stimulates the proliferation and differentiation of myeloid precursors but also enhances the functional.Â .Â .