We conducted a study of unrelated donor bone marrow transplantation (BMT) in 11 children with severe thalassaemia. The conditioning regimen consisted of busulphan, cyclophosphamide and antilymphocyte globulin. All received T-cell nondepleted bone marrow. The median marrow-nucleated cell dose was 4.9 x 10(8) /kg (range; 3.5-8.0 x 10(8) /kg). Median time of granulocyte recovery was 16 days (range; 13-21 days), and of platelet recovery was 39 days (range; 14-196). Grade 2-4 acute graft-versus-host disease (GVHD) developed in six patients (54%), and grade 3-4 in one patient (9%). Three (27%) of 11 evaluable patients had chronic GVHD (limited stage). All 11 patients are alive without thalassaemia after a median follow-up time of 397 days (range; 171-814 days). This study lends support to consideration of unrelated donor BMT as an acceptable therapy to cure severe thalassaemia especially in patients who are young and do not yet show irreversible severe complications of iron overload.