Eight patients with severe combined immunodeficiency received bone marrow cells from their HLA haplotype-identical fathers after bone marrow T cell depletion by rosetting with neuraminidase-treated sheep red cells. Because the method led to the infusion of a small percentage of T lymphocytes (0.1% to 0.3%), cyclosporin was given by continuous intravenous infusion for two months in order to prevent the occurrence of graft-v-host disease (GVHD). Three patients who did have residual nonfunctional T lymphocytes received busulfan and cyclophosphamide before transplantation. Engraftment was observed in seven patients, and severe GVHD was not seen. Two patients died early after the bone marrow transplantation because of prior infections, and a third died at day 90 from a B cell lymphoproliferative syndrome. The five other patients are doing well. Stable engraftment has been achieved with reconstitution of cell-mediated immunity in 5/5 and humoral immunity in 4/5 patients.