We examined granulocyte colony-stimulating factor (G-CSF) receptor (GR) expression on leukemic cells from 44 adults with newly-diagnosed acute myeloid leukemia (AML). GR expression was higher in female patients. G-CSF was administered to AML patients after initial induction therapy without significant acceleration of leukemia, irrespective of GR expression level. G-CSF administration after initial chemotherapy did not adversely influence clinical outcome of GR-positive patients. However, at first relapse, leukemia regrowth was accelerated in 3 of 15 GR-positive patients who received G-CSF after re-induction. It remains to be determined whether leukemia acceleration due to G-CSF contributes to re-induction failure and if G-CSF therapy is a significant risk in relapsed, GR-positive AML patients.