Chronic myelomonocytic leukemia (CMML) is a polymorphous malignant hematological stem cell disorder, characterized by abnormal hyperplasia of mature or immature cells of both monocytic and granulocytic series and with abnormal cellular morphology. It is an independent entity of chronic leukemia, as its prestage course is manifested by refractory anemia with monocytosis and the disease gradually evolves to CMML. In some cases, it finally becomes acute leukemia. In this study, the average white cell count of the patients was 29.3 x 10(9)/L.14 cases had leucocytosis, 7 leucopenia and 5 normal count. The absolute value of monocytes was 19 x 10(9)/L and the proportion of monocytes was 10-87%, with an average of 49%. In the leukopenic group with white cell count less than 4 x 10(9)/L, the absolute value of monocytes was less than 1 x 10(9)/L in 5 of the 7 cases. However, it was noticed that all the 5 cases had a proportion of monocytes greater than or equal to 10%. The authors would like to take this percentage as the diagnostic criteria for CMML, which is different from that adopted in FAB classification of 1982 as well as in the literatures. Statistics showed that P value of M/E, Mo/E, Mo/M were of apparent significance in the differentiation of CMML from normal controls and patients with other hematological diseases such as RA, RAEB, CML, CNL, M4 and M5.