Background/Aim. The use of peripheral blood as a source of hematopoietic stem cells (SCs) is progressively increasing and has nearly supplanted bone marrow transplantation. Interpatient variability in the degree and kinetics of SC mobilization into peripheral blood is an expected event after conventional chemotherapy-based treatment, followed by sequential administration of recombinant granulocyte-colony- stimulating factor (rHu-CSF). In this study, specific factors associated with the application of two different SC-harvesting approaches, including the use of large volume leukapheresis (LVL) vs. repetitive conventional apheresis (RCA), were analyzed. The basic goal of the study was to evaluate the influence of apheresis protocol (collection timing, processed blood volume and cell yield) upon the clinical outcome of transplantation. Methods. Results obtained by LVL (76 pts) and RCA (20 pts - control group) were compared. The SC mobilizing regimen used was cyclophosphamide (4-7 g/m2) or polychemotherapy and rHuG-CSF 10-16 μg/kg of body mess (bm) per day. Cell harvesting was performed using COBE-Spectra (Caridian-BCT, USA). The volume of processed blood in LVL setting was ≥ 3.5 - fold of the patient's circulating blood quantity (ranged from 12.7 to 37.8 l). All patients tolerated well the use of intensive treatment, without any side or adverse effects. Our original controlled-rate cryopreservation was carried out with 10% dimethyl sulfoxide (DMSO) using Planer R203/200R or Planer 560-16 equipments (Planer Products Ltd, UK). Total nucleated cell (NC) and mononuclear cell (MNC) counts were examined by flow cytometry (Advia-2120 Bayer, Germany; Technicon H-3 System, USA). The CD34+ cell surface antigen was investigated by the EPICS XL-MCL device (Coulter, Germany). Results. Performing LVL-apheresis, high-level MNC and CD34+ cell yields (7.6±4.6 × 108/kg bm and 11.8±6.5 × 106/kg bm, respectively) were obtained. As a result, rapid hematopoietic reconstitution ("graft-healing") - on the 9.4th and 12.4th day for granulocytes and platelets, respectively was achieved. Using repetitive conventional apheresis (2-3 procedures), the total MNC count was high (8.2±7.0 × 108/kg bm), but the total CD34+ yield was lower 10.8±9.9 due to inferior CD34+ vs. MNC ratio. Conclusion. The results obtained suggest that well-timed LVL-apheresis increased SC-yield in cell harvest, resulting in faster bone marrow repopulation and hematological reconstitution, as well as better overall clinical outcome of transplantation. These results necessitate additional examinations of CD34+ subsets ratio in cell harvest.