Two cases of Ph1-negative chronic myelogenous leukemia (CML) are described, they were 66-year-old female and 73-year-old male. Both patients shared all of the following features: presence of anemia, thrombocytopenia and leukocytosis with every stage of neutrophilic differentiation, hypercellular bone marrow with hyperplasia of the degranulated neutrophilic series, diminished neutrophilic alkaline phosphatase, elevated serum lysozyme and vitamin B12 level, mosaic pattern of trisomy 8 and normal karyotypes in chromosome analysis, and markedly increased number of CFU-GM. In addition, bcr rearrangement by Southern blot hybridization was not demonstrated in these patients. The diagnosis of chronic myelomonocytic leukemia was not verified, however, because of the absence of monocytosis in peripheral blood. The existence of so-called Ph1-negative CML like these two cases as a diagnostic entity must be further studied.