Purging tumor cells from peripheral blood stem cells (PBSCs) used to treat patients with malignancy is important in the prevention of relapse. Positive selection of CD34+ stem cells using either immunomagnetic methods or an avidin-biotin conjugated CD34 monoclonal antibody binding column can reduce the number of contaminating tumor cells. We describe the management of three patients with malignancy treated using high-dose chemotherapy and enriched CD34+ cell transplantation. PBSCs were mobilized with cyclophosphamide plus recombinant granulocyte-colony stimulating factor (rG-CSF), and then leukophoresis was performed to harvest the PBSCs. The collected cells were positively selected for CD34+ cells using the Cellpro system. The CD34(+)-enriched PBSCs were then cryopreserved in the vapor phase of liquid nitrogen for future reinfusion. All three patients recovered smoothly after transplantation. The mean time to full hematologic recovery was 12 days for white blood cells (> or = 1 x 10(9)/L) and 14 days for platelets (> or = 20 x 10(9)/L), respectively. Partial remission occurred in two patients who were disease free for more than 4 years, and in one patient who died of hepatic failure with liver cirrhosis 5.5 months posttransplantation.