Counterflow centrifugation elutriation (CCE) has been used to separate moderate quantities of bone marrow (BM) into distinct cell populations for further in vitro investigation. Recently, this technique was employed to reduce the incidence of graft-versus-host disease (GVHD) in human allogeneic bone marrow transplantation (BMT) by removing the majority of mature lymphocytes from the graft. Unfortunately, current methods employing the small (J6-B) elutriator rotor require time consuming preseparation steps and multiple runs. We report our experience with a fixed rotor speed, two-flow rate elutriation procedure using the new Beckman JE-10X rotor system which can separate more than 10(10) nucleated BM cells in 30 min. Three fractions were obtained which differed in size, morphology, and immunologic capacity. The large cell fraction is suitable for allogeneic BMT since it is radically depleted of mature T lymphocytes and retains high clonogeneic capacity.