Alpha-interferon (alpha-IFN) has been used in relapsed CML post-BMT, cytogenetic responses being attained in a number of cases (33 to 42%). In first chronic phase-CML patients such cytogenetic response has been correlated with the disappearance of the bcr region rearrangement, as seen with Southern-blot, but when RT-PCR is used only a small number of patients maintain undetectable traces of the Ph1 clone. A case of CML in haematological and cytogenetic relapse after BMT is reported who showed criteria of "accelerated" phase and, after treatment with alpha-IFN achieved haematologic, cytogenetic and molecular remission (Southern-blot and PCR negative) and disappearance of the abnormal clone with recovery of the donor haemopoiesis. The duration of the alpha-IFN cytogenetic response is longer than that of BMT (5 vs 3.5 yr), which is noteworthy. Taking the low toxicity of alpha-IFN into account, as compared with that of the other choices (a second BMT, IL2), this treatment should be offered to all patients with cytogenetic relapse after BMT.