We report here 16 autologous bone marrow transplantations (ABMT) for poor prognosis B or pre-B malignancies (16 acute lymphoblastic leukemias (ALL), three Burkitt lymphomas, one multiple myeloma) in 11 adults and five children where in vitro purging was accomplished by means of floating immunobeads. This method was developed to avoid non-specific killing by complement or toxin or batch-to-batch variability and provides a 3 log reduction of tumor in a model of B lymphoid malignancies. Low density bone marrow mononuclear cells were incubated for 30 min at 4 degrees C with anti CD10 (ALB2 Immunotech) and/or anti CD19 (Bg4) monoclonal antibodies (MoAb) and then mixed with low density polypropylene beads precoated with a rat antimouse MoAb. After 1 h at 4 degrees C the beads with target cells were decanted; the depleted marrow was collected through a microfilter and cryoperserved. After immunodepletion the recovery of nucleated cells was 75% with a median of 0.75 x 10(8) cells/kg (range 0.3-3.6) and the recovery of hematopoietic progenitors was 83% with a median of 2.9 x 10(4) CFU-GM/kg. The conditioning regimen consisted of busulfan 16 mg/kg and melphalan 140 mg/m2 for three patients, fractionated total body irradiation (TBI) following melphalan 140 mg/m2 for nine patients, TBI and cyclophosphamide 120 mg/m2 for two patients and TBI associated with melphalan and cyclophosphamide for two patients.(ABSTRACT TRUNCATED AT 250 WORDS)