It was the aim of our study to determine the collection efficiency and yield of CD34-t cells in 88 cancer patients (pts, 44 males144 females) who underwent 154 large-volume leukaphereses (LV-LPs). The diagnoses were as follows: 18 patients had Non-Hodgkin's lymphoma, 9 Hodgkin's disease, 24 multiple myeloma, 6 acute leukemia, 27 breast cancer, and 4 patients had solid tumors of different types. During the course of LV-LPs, 20 liters (1) of blood were processed at a median flow-rate of 85 mllmin (CS 3000 Baxter) and 130 mllmjn (COBE Spectra), respectively. Peripheral blood stem cells (PBSC) were collected following granulocyte colony-stimulating factor (G-CSF)supported cytotoxic chemotherapy. A 31% and 21% mean decrease in the platelet and white blood count was noted at the end of the LV-LPs when compared with the pre-leukapheresis values. The aphereses were well tolerated without adverse effects. The level of circulating CD34f cells was closely related to the number of CD34f cells contained in the respective leukapheresis product (R = 0.89, P < 0.001). Compared with 270 patients who underwent 838 regular 10 1 LPs, the yield of CD34+ cellskg was almost two-fold greater (4.84 t 0.63 X lo6 [Mean i SEMI vs. 2.60 i 0.16 X lo6, P < 0.001). The antigenic profile of CD34f cells was assessed in 54 separate products collected on the occasion of 27 LV-LPs following the processing of 10 1 and 20 I, respectively. The intra-individual comparison included differentiation-as well as lineage-associated markers (CD38, Thy-1, c-kit, CD33, CD4SRA). No difference in the subset composition was observed between the first and second product, arguing against a preferential release of particular CD34+ cell subsets during the procedure. As shown by molecular biological or immunocytochemical examination, the likelihood of harvesting malignant cells using large-volume aphereses was not increased in comparison with regular leukaphereses. Single harvests of 22.5 X 10' CD34+ cellskg could be obtained in 74% of the patients, compared with 52% in case of regular LPs. As the majority of patients were autografted with more than 2.5 X lo6 CD34+ cellskg following high-dose therapy, hematological recovery in general was rapid and not related to the type of apheresis product used. Considering patient comfort and savings in resource utilization, large-volume leukaphereses have become the standard procedure for PBSC collection in our center.