In advanced chronic myeloid leukaemia patients, STI-571 produces complete haematological response in most cases and cytogenetic response in up to 50%. However, these patients often suffer periods of pancytopenia, which can lead to life-threatening complications, and is probably due to the small number of residual normal stem cells. We have re-infused peripheral blood stem cells collected at diagnosis, in a patient, while maintaining STI-571 treatment. The patient recovered from aplasia, with Philadelphia-negative haematopoiesis. Discontinuing an effective treatment because of persistent aplasia is a major concern; this method circumvents this problem inpatients who have undergone a stem cell harvest at diagnosis.