A 57 year-old-female was incidentally found to have leukocytosis in September 1988. Physical examination revealed anemia and marked hepatosplenomegaly. Her WBC count was 33,400/microliters with 95% mature neutrophils showing toxic granules. Her neutrophil alkaline phosphatase score was 482, and serum VB12 14,600 pg/ml. Serum immunoglobulin concentrations were 582 mg/dl for IgG, 3,628 mg/dl for IgA and 48 mg/dl for IgM. IgA was determined as monoclonal origin of lambda type. Bone marrow aspiration revealed a hypercellular marrow with active granulocytopoiesis and increased plasma cells. Cytogenetic study revealed normal karyotype. The bcr rearrangement was negative for bone marrow cells. An electronmicroscopy demonstrated fibrillar inclusions in granulocytes. We diagnosed this case as a chronic neutrophilic leukemia (CNL) associated with multiple myeloma. She was treated with a course of low dose busulfan without beneficial response. She was admitted for development of huge subcutaneous hematoma of left waist in October 1990. Laboratory findings were: Hb 7.0 g/dl, WBC 55, 300/microliters, Platelets 3.3 x 10(4)/microliters, and IgA 6,607 mg/dl. She required frequent transfusions. She died of pneumonia in July 1991. The peculiar fibrillar inclusions with CNL has not been reported so far. The origin and significance of such structure remains uncertain.