A new procedure for enrichment of marrow precursors and removal of T lymphocytes from large volumes of human bone marrow, involving initial differential agglutination of T lymphocytes and mature marrow elements with soybean agglutinin, followed by rosetting with sheep red blood cells, was used to fractionate marrow cells from an HLA-A, B, DR non-identical, MLC non-reactive, paternal donor for transplantation into an infant with acute leukaemia. This transplant became completely engrafted and resulted in full recovery of normal, donor-derived haematopoietic function without graft-versus-host disease, sustained for 11 weeks after transplantation, at which time the patient's leukaemia recurred. Subsequently, the patient received chemotherapy and achieved a remission with regeneration of normal marrow cells of donor origin. The patient's course demonstrated the potential of lectin-separated marrow grafts to restore durable haematopoiesis, without graft versus host disease, in a lethally irradiated allogeneic host.