Six patients with a myelodysplastic syndrome (MDS) were treated with bone marrow transplantation (BMT) using partially-matched related (3) or unrelated (3) donors. Patients' ages ranged from 7 to 31 years (median, 10 years). Bone marrow karyotype abnormalities were present in five patients included four with monosomy 7 and one with trisomy 8. One patient was in complete remission before transplant; the remaining five had excess of blasts or were undergoing leukemic transformation. Donor, and recipient were mismatched at the DR locus (2), A locus (2), B locus (1), or A and B loci (1). Conditioning included busulfan, cytarabine, cyclophosphamide, methylprednisolone, and total body irradiation. Cyclosporine was started on day -1. Marrows were T-cell depleted using a monoclonal antibody (MoAb) (CD3) and normal rabbit serum. Four patients engrafted routinely. One patient died of aspergillosis before engraftment (day 12) and one patient failed to engraft on first attempt, but engrafted following additional preparation. Median time to neutrophils greater than 500/microL and platelets greater than 25,000/microL were 16 and 19 days, respectively. Acute graft-v-host disease (GVHD) was less than or equal to grade II in all patients. One patient died with recurrent disease (day 257). One patient died at day 515 of pancreatitis and respiratory failure. Three patients are alive and disease-free at 240, 395, and 560 days post-BMT including two patients with unrelated donors. Partially matched T-depleted bone marrow from related or unrelated donors may be effective, and possibly curative therapy for patients with MDS who lack a histocompatibility locus antigen (HLA)-identical sibling donor.