Autologous bone marrow transplantation (BMT) was utilized as therapy for 23 patients with acute lymphoblastic leukemia (ALL) in second or greater remission. Bone marrow was treated in vitro with a combination of monoclonal antibodies, consisting of BA-1, BA-2, BA-3, and baby rabbit complement (BRC'). All patients were prepared for transplantation with cyclophosphamide and fractionated total body irradiation. Engraftment occurred in all 23 patients. Seven of 23 patients remain relapse-free from six to 32 months (median, 21.4 months) posttransplant. Failures were due to relapse with the exception of one patient who died of infection. This study demonstrates that autologous BMT using in vitro marrow treatment with BA-1, BA-2, BA-3, and BRC' is safe, allows engraftment, and results in prolonged survival for some patients with ALL in second or greater remission.