Three patients with Wiskott-Aldrich syndrome received transplants of marrow from their HLA-A, B, C, D identical siblings after myeloablation with busulfan, 2 mg/kg/day x 4 days, followed by immunosuppression with cyclophosphamide, 50 mg/kg/day x 4. Sustained engraftment of lymphoid and hematopoietic elements was documented in each case. Platelet counts in excess of 100,000/cu mm were restored 20--50 days posttransplant and remain in the normal range 6--12 mo later. Platelets exhibit normal size and in vitro aggregation. The patients produce isoagglutinins and antibodies to other polysaccharides. The use of busulfan in moderate dosages as a myeloablative agent, coupled with cyclophosphamide, may offer an improved alternative to the use of lethal total body irradiation as a preparative regimen for complete correction of Wiskott-Aldrich syndrome by marrow transplantation.