Improvement of the collection efficiency (CE) of the Fenwal CS3000 plus in collecting circulating progenitor cells (CPC) might diminish the number of leukapheresis procedures (LP) required to obtain the CPC required to assure engraftment. We analyzed whether adjustment of the optical setting (location 71,L71) to the number of MNC present in the peripheral blood could enhance the CE of the MNC. Thirty-five patients underwent 121 LP with an adjusted L71. We compared the results retrospectively with 26 LP performed with a fixed L71 (1:100) in 12 patients. The CPC were mobilized with chemotherapy followed by subcutaneous administration of granulocyte colony-stimulating factor (G-CSF) in both groups. Adjustment of the L71 did neither improve the CE of the MNC, the estimated CE of CD34+ cells nor diminished granulocyte contamination. For the total 121 LP with an adjusted L71 and for the total 26 LP with a fixed L71 the mean CE of MNC were, respectively, 44.6 +/- 18.3% and 46.4 +/- 14%. The mean granulocyte contamination, determined by manual white blood cell differentiation, was 1.7 +/- 2.3% for the adjusted L71 group and 2.3 +/- 3 for the fixed L71 group. There was no difference in the median number of LP required to obtain 3 x 10(6) CD34+ cells/kg between both groups. We found a weak significant correlation between WBC and pre-LP MNC count and the CE of MNC (r = 0.36, P = 0.012, resp.r = 0.33, P = 0.023), but no correlation between the CE of MNC and the estimated CE of CD34+ cells (r = 0.24, P = 0.113). In conclusion, adjustment of the L71 to the MNC did not improve the CE of MNC of the Fenwal CS3000. The lack of correlation between the CE and MNC and the estimated CE of CD34+ cells should be further explored.