Two patients with chronic myelogenous leukemia (CML) and basophilic transformation are reported because of unusual clinical and cutaneous features. One patient had the hyperhistaminemic syndrome (HHS) during relapse of the accelerated phase of CML. The literature on this topic is reviewed. The second patient had a basophilic crisis in the second year of CML. More than 100,000/cu mm basophils in the blood contrasted with infiltrates of eosinophils appearing in the skin and central nervous system. This striking cellular dichotomy suggested that the basophilic transformation of CML had acquired features mimicking the hypereosinophilic syndrome.