A case of hybrid phenotypic chronic myelomonocytic leukemia (CMMoL) transformed from a hematological remission state of severe aplastic anemia is reported. A 63-year-old woman was admitted to our hospital with complaints of easy fatigability and dizziness in December 1978. A diagnosis of aplastic anemia was made from findings of pancytopenia and hypoplastic marrow without dysplasia, and she was treated successfully with mepitiostane. Seven years later, anemia and thrombocytopenia reappeared with monocytosis. On the second admission, the peripheral blood showed a white blood cells count of 3.5 X 10(3)/microliters with 54% monocytes. The bone marrow was hypercellular with monocytosis, and dysplasia of three cell lineages was noted. A diagnosis of CMMoL was made. Cytogenetic analysis of bone marrow cells revealed a karyotype of 45 XX, -7, 11q-, and surface markers were polyphenotypic, including CD20+, CD14+ and CD13+. This is the first report of CMMoL with biphenotype which was transformed from aplastic anemia.