A 21-year old male patient with Philadelphia chromosome-positive chronic myeloid leukaemia received an autologous bone marrow transplant in consolidation of the 2nd chronic phase. The bone marrow had been treated with mafosfamide in adequate doses. The post-transplantation course of the disease was marked by an inversion: the duration of the 2nd chronic phase was more than 4 times longer than that of the first one, suggesting some degree of effectiveness of autologous bone marrow transplantation performed in the 2nd chronic phase and/for of the in vitro treatment of the bone marrow with mafosfamide. Cytogenetic monitoring was pursued throughout the course of leukaemia: regression of the Philadelphia chromosome was only partial and transient, and 3 clones appeared, each of them involving chromosome 1, for which mafosfamide was most probably responsible.