Neutropenia in the newborn is often associated with sepsis, maternal hypertension, or prematurity. We describe a 654-g infant born at 30 weeks' gestation by cesarean section due to severe maternal hypertension. His course was complicated by five episodes of sepsis, including three with group B streptococcus. The results of hematologic and immunologic studies were normal except that absolute neutrophil counts were low (less than 1 x 10(9)/L) with intermittent increases during sepsis. Human recombinant granulocyte colony-stimulating factor administered subcutaneously (10 micrograms/kg per day initially) resulted in an absolute neutrophil count of greater than 30 x 10(9)/L within 2 weeks. The dosage was lowered and the absolute neutrophil counts were maintained at 8 to 12 x 10(9)/L with no further septic episodes. The human recombinant granulocyte colony-stimulating factor therapy was discontinued after 7 months, and the patient remained healthy with an absolute neutrophil count of greater than 2 x 10(9)/L. Thus, treatment with human recombinant granulocyte colony-stimulating factor may be useful as a temporary measure for neonatal neutropenia associated with sepsis. A controlled, clinical trial is warranted.