Thirty patients with severe aplastic anemia had no transfusions of blood products until just before marrow transplantation from HLA-identical family members. They were conditioned for grafting with cyclophosphamide, 50 mg/kg body weight on each of 4 successive days. All 30 had prompt initial marrow engraftment, which was sustained in 27. Twenty-five of the 30 are alive between 9 to 84 (median, 19.5) months. The actuarial projection of survival for 2 to 6 years is 75%. Twenty of the 25 surviving patients have no problems. Five have chronic graft-versus-host disease, resolving in two and active in three. Five patients died with infection or hemorrhage, four of whom had graft-versus-host disease. These data show that early transplantation should be carried out before transfusions are given for any patient with severe aplastic anemia who has an HLA-identical family member. If sensitization to minor transplantation antigens contained in blood products is avoided, the incidence of marrow-graft rejection will decrease, and survival will improve.