A patient with hypoplastic acute myelogenous leukemia (AML) who achieved remission with granulocyte colony-stimulating factor (G-CSF) alone is reported. The 59-year-old male patient received antibiotics and G-CSF but not any antileukemic drugs because of ongoing pneumonia. After 2-week administration of G-CSF, he achieved complete remission and his pneumonia improved. Since leukemia relapsed after 3 months, he received G-CSF again for 5 weeks, but failed to be in remission this time. He underwent antileukemic chemotherapy and achieved second remission. When he suffered from a second relapse after 7 months, intensive chemotherapy was commenced but was stopped on the 2nd day since his general condition became very poor due to septicemia. He began to receive G-CSF again and achieved third complete remission after 3 weeks. In vitro studies showed that G-CSF did not stimulate proliferation of the patient's blast cells although they expressed G-CSF receptor on their surface. Moreover, G-CSF induced differentiation of the blast cells into segmented neutrophils in vitro. According to the literature, in all of the 12 patients with AML who were reported to achieve remission by G-CSF the course was complicated by infection, and 7 of the patients were diagnosed as hypoplastic acute leukemia. It is suggested that not G-CSF alone but G-CSF with infection could induce remission, which might be related to a differentiation effect of G-CSF in this case. G-CSF is not only safe but also useful for remission induction therapy in hypoplastic acute leukemia.