20 CML patients with hematological (5 pts) or only cytogenetic (15 pts) relapse occurring after allogeneic BMT have been treated with alpha-2b-interferon (IFN) at a starting dose of 5 x 10(6) IU/m2, subcutaneously, three times a week. All 5 patients with hematological relapse achieved hematological remission without reduction of bone marrow Ph1-positive cells. With a median follow-up of 43 months (range 6-48) from the hematological relapse, 3 patients are alive and 2 patients died from non-lymphoid blast crisis. 7 out of 15 patients with only cytogenetic relapse remain in hematological remission at a median of 37 months (range 3-45) from cytogenetic relapse, with 2 patients achieving complete cytogenetic remission confirmed at the molecular level by disappearance of the bcr rearranged band. With a median follow-up of 21 months (range 6-46), 8 patients progressed from cytogenetic to hematological relapse: 4 patients died from blast crisis and the other 4 patients are currently alive in chronic phase. For the 15 patients, the actuarial survival from BMT is 71% at 5 years.