The potential role of unrelated donor cord blood transplantation (UD-CBT) in adults is not well established. We report the results of UD-CBT in nine adult patients with chronic myeloid leukemia (CML). The median age was 27 years (range, 19-41 years), and the median weight was 62 kg (range, 45-78 kg). At transplant, six patients were in chronic phase (five in first, and one in second), two in blast crisis, and one in accelerated phase. Eight had received intensive chemotherapy, and three had undergone autologous peripheral blood hematopoietic stem cell transplantation. Four had received interferon with no cytogenetic response, and only three underwent UD-CBT within 1 year of diagnosis. After serological typing for class I antigens, and high-resolution DNA typing for DRB1, the degree of HLA match between patients and cord blood (CB) units was 4/6 in six cases and 5/6 in three cases. The median number of nucleated cells infused was 1.7 x 10(7)/kg (range, 1.2 to 4.9 x 10(7)/kg), and was above 2 x 10(7)/kg in only two cases. All patients received thiotepa, busulfan, cyclophosphamide and anti-thymocyte globulin as conditioning; cyclosporine and prednisone for graft-versus-host disease (GVHD) prophylaxis; and G-CSF from day +7 until engraftment. All seven evaluable cases engrafted. The median time to reach an absolute neutrophil count > or =0.5 x 10(9)/l and > or =1 x 10(9)/l was 22 days (range, 19-52 days) and 28 days (range, 23-64 days), respectively. In the four patients evaluable for platelet recovery time to levels of > or =20 x 10(9) platelets/l, > or =50 x 10(9) platelets/l, and > or =100 x 10(9) platelets/l, these ranged from 50 to 128 days, 60 to 139 days, and 105 to 167 days, respectively. Three patients developed acute GVHD above grade II, and three of the five patients at risk developed extensive chronic GVHD. Four patients, all transplanted in chronic phase, remain alive in molecular remission more than 18, 19, 24 and 42 months after transplantation. These preliminary results suggest that UD-CBT may be considered a reasonable alternative in adults with CML who lack an appropriate bone marrow donor.