There are at least two reasons for the improved survival of patients with AA who were treated by HLA-identical HCT. One is the decreased incid¬ence of graft rejection. The decline in rejection has resulted from the more judicious use of transfusions before HCT, the removal of sensitiz¬ing white blood cells from transfusion products, and improvements in the immunosuppressive qualities of the conditioning programs used to prepare patients for transplantation. Irradiation-based programs have been effective but at the price of more transplant-related complications, and the CY and ATG combination is just as successful in preventing rejection with better long-term survival. With regard to transfusions before HCT, in vitro irradiation of all blood products may further reduce the risk of sensitization to tninor histocompatibility antigens in the future [STORB, et al 1988].