The management of CML patients with some evidence of disease after BMT depends on the molecular, cytogenetic and hematological findings of relapse. Presently, a number of technical and biological problems do not allow to draw any definitive conclusion on the prognostic significance of Minimal Residual Disease detected by PCR. A positive PCR, particularly if observed late after BMT, leads to increase the frequency of cytogenetic examinations, but a therapeutic intervention is not justified. The criteria to define the cytogenetic relapse are not still established. Therefore it is difficult to interpret the reappearance of Ph-1 chromosome after BMT as disease recurrence invariably progressing towards the hematological phase. However, alpha-Interferon, donor buffy-coat infusion or their association should be considered in the treatment of patients for whom the cytogenetic relapse has been confirmed. The therapeutic approach to patients with hematological relapse is mainly depending on the phase of disease. The single, sequential or combined use of chemotherapy, alpha-IFN, donor buffy-coat infusion and second transplant has been shown to be effective in restoring donor hematopoiesis in several patients who relapsed either in chronic or advanced phase. Prospective, randomized, multicentre trials on CML relapse after BMT should be planned.