Basophils in peripheral blood and bone marrow in 25 cases with chronic myelogenous leukemia (CML) were counted and morphologically classified by our improved method; basophilis were classified into Ⅰ to Ⅴ types. The Ⅲ and Ⅳ types were subclassified to S type with sharply defined granules and diffuse N type. This classification was adapted for basophilograms. The basophilogram in healthy controls showed a left type and that in CML generally a right type. It shifted to the left approaching to the normal type in the cases with remission by chemotherapy. In relapsing patients with CML, the basophilogram clearly shifted to the right. The basophilogram seen in 2 cases with the pre-stage of blastic crisis of CML indicated a definite right type. It was shown that an increase of S type occurred in the relapsing stage. Therefore, appearance of S type as well as a right type in basophilogram would be a useful clue to follow CML patients clinically. A basophils of S type was considered to be immature. The bone marrow basophilogram was shown to be more shifted to the right than that of peripheral blood, and this tendency became more remarkable in relapse. Presence of a right type in basophilogram and appearance of S type are significant to observe the clinical course in CML patients, especially for judging acute exacerbation.