A 56-year-old female was admitted for the examination of leukocytosis in May, 1982. The hematological examination showed hemoglobin 12.0g/dl, platelets 14.5 X 10(4)/microliters and leukocytes 18,000/microliters with 28% of monocytes. A bone marrow aspiration revealed granulocytic hyperplasia. Granulocytes showed nuclear abnormalities, such as folding or lobulation. From these data, a diagnosis of chronic myelomonocytic leukemia (CMMoL) was made and followed with no treatment for 2 years. However, fever, bone pain, anemia, thrombocytopenia and the increase of monoblasts in the peripheral blood and bone marrow were observed in May, 1984. These findings indicated that she was in the blastic phase. She was treated by intensive combination chemotherapy (BHAC-AMP), but did not attain any remission. Therefore, a small dose of N4-behenoyl-1-beta-D-arabinofuranosylcytosine (BH-AC; 1 mg/kg/day) was administered for 70 days. As a result, complete remission was obtained and continued for 37 months with the same therapy. The experience of this case suggests that small dose of BH-AC could be applied to a case of CMMoL in blastic crisis.