Thirty-nine children with leukemia were entered into a bone marrow transplantation study comparing the use of unrelated donors who were HLA-Dr identical and matched at least with three of the four HLA-A or B loci, with haploidentical related donors. Although marrows were prepared by T lymphocyte depletion in vitro, the rejection rate of marrow in these patients was only 13% (5/39). Four patients had early rejections, and three of these four had autologous recovery immediately without evidence of leukemic recurrence. The fifth had a delayed rejection occurring approximately 2 1/2 months after transplant. These results were achievable by an ablative regimen incorporating increased immunosuppression. Although the small sample size does not yet permit evaluation of outcome comparing one donor type versus another, the early findings document a high rate of successful engraftment.