Neutropenia is a mild and transient manifestation of neonatal lupus syndrome (NLS) in the second or third month of life. The authors describe a newborn with an early-onset severe neutropenia due to anti-Ro/SSA. In the second day of life, neutropenia has been treated with recombinant human granulocyte colony-stimulating factor (rh-G-CSF). This is the first case in which rh-G-CSF was used in NLS, and the authors studied the pharmacologic action of the drug in relationship to the pathophysiology of NLS.