It is logical to expect that large-volume leukapheresis may be able to collect adequate numbers of PBSC with fewer procedures. To date, there is no agreement on the optimal volume of leukapheresis. Therefore, in this study we compared 8 l volume with 12 l and assessed whether a 50% increase in the blood volume processed would decrease the number of leukaphereses each patient needed to collect > or =2.5 x 10(6) CD34(+) cells/kg in normal mobilizers. PBSC mobilization was done with cyclophosphamide etoposide followed by rhG-CSF in all patients. Forty patients were randomized to undergo 8 l leukaphereses (n = 20 patients) or 12 l leukaphereses (n = 20). The median numbers of leukaphereses required in order to collect > or =2.5 x 10(6) CD34(+) cells/kg in patients processed with 8 l and 12 l were 1 (range 1-5) and 1 (1-4), respectively (P = 0.50). The median number of total nucleated cells (TNC) collected per patient was greater for the 12 l group (7.47 x 10(8)/kg vs 3.90 x 10(8)/kg, P < 0.001), as was the median number of total mononuclear cells (TMNC) (4.26 x 10(8)/kg vs 2.16 x 10(8)/kg, P < 0.001), whereas there was no difference between the two groups for the median number of CD34(+)cells collected per patient (8.94 x 10(6)/kg vs 8.60 x 10(6)/kg, P = 0.85). The TNCs and TMNCs collected per leukapheresis were again greater for the 12 l group (3.64 x 10(8)/kg vs 1.91 x 10(8)/kg, P = 0.001 and 2.17 x 10(8)/kg vs 0.88 x 10(8)/kg, P < 0.001), whereas there was no difference between the two groups for the median number of CD34(+) cells collected per leukapheresis (3.98 x 10(6)/kg vs 3.26 x 10(6)/kg, P = 0.90). This study showed that there is no difference between 8 l and 12 l volumes in regard to collected CD34(+) cells/kg and also the use of a 12 l leukapheresis volume did not decrease the number of leukaphereses performed compared with a 8 l leukapheresis volume. In fact, the use of the larger leukapheresis volume had the disadvantage of adding 60 min to the time the patient was on the machine.