We prospectively evaluated the efficacy of T-cell-depleted bone marrow transplantation (BMT) in adults with de novo acute nonlymphocytic leukemia (ANLL) in first complete remission (CR), with regard to relapse-free survival and incidence of graft-versus-host disease (GvHD). Thirty-one patients older than 16 years (range, 16.5 to 43.2) received T-cell-depleted grafts for this purpose from related HLA/MLC- compatible donors. Twelve of the patients were older than 30 years at the time of transplantation. Patients were prepared with hyperfractionated total body irradiation (HFTBI; 1,375 to 1,500 cGy) and high-dose cyclophosphamide (120 mg/kg). T cells were removed from the marrow grafts by a two-step soybean lectin agglutination and sheep red blood cell (sRBC)-rosette procedure, achieving a 2.5- to 3-log depletion of clonable T lymphocytes. No additional prophylaxis against GvHD was administered. The median age at transplantation was 28.8 years; the median interval from diagnosis to transplantation was 3.8 months, and from CR was 2.7 months. Seventy-four percent received consolidation after remission induction therapy. The product-limit estimate of disease-free survival (DFS) at 3 years is 45% (95% confidence interval [CI], 24% to 66%), and the cause-specific probability of relapse is 13%. The median follow-up of the survivors is 72 months (range, 34.5 to 95.6). Median time to achieve a sustained absolute neutrophil count of 500 or greater was 16 days, and to maintain an untransfused platelet count of 20,000 or greater was 20 days. Five patients suffered immune-mediated graft rejection. Three patients developed grade I to II acute GvHD limited to the skin, which resolved promptly with brief courses of systemic steroids. None of the patients has developed clinically apparent chronic GvHD or a secondary lymphoproliferative disorder, and no patient is receiving immunosuppressive therapy. T-cell-depleted BMT by the method reported here is a favorable option as postremission therapy for adults with de novo ANLL in first remission who have an HLA/MLC-compatible related donor, and it is not associated with an increased risk of relapse posttransplant.