The availability of granulocyte colony-stimulating factor (G-CSF) has influ
enced the management of neonates with neutropenia. Since the first use of G
-CSF in a neonate with neutropenia, much has been learned about the cellula
r sources and physiologic roles of G-CSF. This article reviews our present
understanding of G-CSF and its cognate receptor in the fetus and neonate.