A 93-year-old patient with hypoplastic acute monocytic leukemia (AMoL) achieved a complete remission after macrophage colony-stimulating factor (M-CSF) therapy. Initially, the patient was treated with a low dose of cytarabine, but this treatment proved ineffective. M-CSF was administered for 14 days by drip intravenous infusion, 800 x 10 4 units per day. After a gradual decrease in the number of leukemic cells, a rapid increase in neutrophils was observed in the peripheral blood, and a bone marrow examination 22 days after discontinuation of M-CSF medication revealed a complete remission. These findings suggest that M-CSF may be useful in treating some elderly patients who have hypoplastic AMoL.