A seventy-five-year-old female with general fatigue, high fever and anemia was admitted. Her chest X-ray film revealed pneumonia. She was diagnosed as RAEB-t with the normal karyotype by peripheral blood film and bone marrow aspiration; 125 micrograms/ml of G-CSF was administered s.c. daily in order to increase neutrophil count because of the prolongation of pneumonia. Her blast cells in both peripheral blood and bone marrow showed a remarkable increase by G-CSF. After the cessation of G-CSF administration, blast cells decreased rapidly, and neutrophil count in the peripheral blood increased. Her pneumonia was then cured. After 5 months of stable hematological state, 60% of her bone marrow cells became occupied by blast cells again. So 2 consecutive courses of 14 days p.o. administration of 1,200 mg MST-16/day were tried. Three months after the first MST-16 trial, her bone marrow showed complete remission (CR) which lasted about 4 months. But she died of sepsis after the first relapse. Her bone marrow in CR still revealed several features of dyspoiesis.