The limitation of mismatched BMT is fatal graft vs. host disease (GVHD). We processed haplotype mismatched parental marrow with SBA to enrich for stem cells and reduce GVHD and successfully treated 6 patients with severe combined immune deficiency disease. HLA chimerism was found within 3 weeks post BMT. All the patients demonstrate T cell and 2 have evidence of B cell engraftment. T cell numbers and responses to phytohemagglutinin (PHA) and alloantigen pre and post BMT are:In #2,5,6 who required pre BMT immunosuppression for maternal GVHD, neutrophil, RBC, and platelet engraftment occurred by days 11,26,32 respectively. No immunosuppression was given post BMT. 2 patients had no GVHD, 3 had transient rash/fever, and only 1 developed persistent rash. Patients are now 3 to 17mo. post BMT. These results demonstrate that treated mismatched BMT can result in engraftment without significant GVHD and can be used for patients who otherwise have limited hope for survival.