The chronic myelogenous leukemia [CML] is a clonal disease of hematopoietic stem cells with unknown etiology. The incidence is around 2/100,000/year, the median age at diagnosis about 47 years. The course of CML is characterized by a chronic phase with few symptoms and good therapeutic response of about 4 to 5 years duration and by transition to a prognostically unfavourable blast phase of about 3 months duration. Therapy of choice, at present, is early allogenous bone marrow transplantation [BMT], which is curative in 40 to 80% of transplanted cases. In patients below 55 years, a donor search should be started at the earliest possible time after diagnosis. Drug therapy of choice are interferon alpha [IFN] and hydroxyurea, which are both superior to busulfan with regard to duration of chronic phase and survival. Complete cytogenetic remissions are observed in 5 to 9% of IFN-treated patients in randomized studies, but virtually all remain positive for bcr/abl by PCR. Whether and in how far IFN is superior to hydroxyurea appears, at least in part, to depend on the treatment intensity with hydroxyurea and on patients characteristics. In analyzing median survival times, the risk profiles of the patients have to be considered. In the future, intensive chemotherapy with or without autografting might play an important role in the therapy of chronic-phase CML. Forthcoming trials have to consider both, conventional and new experimental treatment modalities. An example is the treatment strategy of the ongoing randomized study of the German CML Study Group which compares allogenous BMT with the best available drug therapy and, in addition, analyses the influence of intensified drug therapy on survival.