Based on recent fetomaternal microchimerism/tolerance theory, two children with acute lymphoblastic leukemia underwent non-T-cell-depleted hematopoietic stem cell transplants (SCT) from haploidentical HLA 2 loci-mismatched family donors (one from a sibling, one from the mother). Engraftment was achieved in two patients. In two recipients, acute graft-versus-host disease was limited to grade II or less, and no chronic graft-versus-host disease developed. Both of these patients have maintained complete remission for more than 8 months post-SCT. Non-T-cell-depleted SCT from haploidentical HLA 2 loci-mismatched family donors seems feasible if microchimerism is detectable.