The administration of recombinant human granulocyte colony-stimulating factor (G-CSF) following chemotherapy, has been shown, in controlled randomized trials, to decrease the incidence of febrile neutropenic episodes, the duration of severe neutropenia and intravenous antimicrobial therapy, and the length of hospitalization. This review focuses on the evolving role of G-CSF in bone marrow and peripheral blood stem cell transplantation, and in hematopoietic stem cell mobilization.