We studied the outcome of BMT in 38 consecutive CML patients in CP1 who received transplants depleted of lymphocytes using counterflow centrifugation. In all patients the conditioning regimen was intensified by the addition of anthracyclines. Donors were HLA, MLC-identical siblings. Six patients (16%) died within 6 months. All 37 patients with a follow-up of more than 0.5 months engrafted and only one (3%) suffered from acute GVHD > or = grade 3. Chronic GVHD was evaluable in 33 patients and was extensive in six (18%). The projected 5-year probabilities of hematologic, cytogenetic and molecular relapse were 30% (95% confidence interval (CI), 10-49%), 35% (95% CI, 14-56%), and 34% (95% CI, 13-55%), respectively. The projected 5-year probability of survival was 68% (95% CI, 50-86%). Projected at 5 years, probabilities of leukemia-free survival (LFS) in hematologic, cytogenetic and molecular remission were 55% (95% CI, 37-73%), 51% (95% CI, 32-69%), and 51% (95% CI, 32-70%), respectively. All patients with relapse but one who relapsed in blastic phase were treated with retransplantation (n = 1) or with the infusion of lymphocytes (n = 6). Six patients regained second hematologic remission and five entered second cytogenetic and molecular remission. Including these patients, the probability of survival in first or second hematologic remission at the end of follow-up was 68% (95% CI, 50-86%). The probabilities of survival in first or second cytogenetic and molecular remission at the end of follow-up were both 61% (95% CI, 42-80%). We advocate revaluation of T cell depletion of donor marrow for patients with CML-CP1, especially for those at high risk of developing GVHD.