BACKGROUND: We investigated the characteristics of the mononuclear cells remaining in the leukoreduction system (LRS) chambers of Trima Accel(R) in comparison with those of standard buffy coat cells, and evaluated their potential for differentiation into dendritic cells. METHODS: Twenty-six LRS chambers of Trima Accel(R) were collected after platelet pheresis from healthy adults. Flow cytometric analysis for T, B, NK, and CD14+ cells was performed and the number of CD34+ cells was counted. Differentiation and maturation into dendritic cells were induced using CD14+ cells seperated via Magnetic cell sorting (MACS(R)) Seperation (Miltenyi Biotec Inc., USA). RESULTS: Total white blood cell (WBC) count in LRS chambers was 10.8x108 (range 7.7-18.0x108). The median values (range) of proportions of each cells were CD4+ T cell 29.6% (18.7-37.6), CD8+ T cell 27.7% (19.2-40.0), B cell 5.5% (2.2-12.1), NK cell 15.7% (13.7-19.9), and CD14+ cells 12.4% (8.6-32.3) respectively. Although total WBC count was significantly higher in the buffy coat (whole blood of 400 mL) than the LRS chambers, the numbers of lymphocytes and monocytes were not statistically different. The numbers of B cells and CD4+ cells were significantly higher in the buffy coat than the LRS chambers (P<0.05). The median value (range) of CD34+ cells obtained from the LRS chambers was 0.9x10(6) (0.2-2.6x10(6)). After 7 days of cytokine-supplemented culture, the CD14+ cells were successfully differentiated into dendritic cells. CONCLUSIONS: The mononuclear cells in LRS chambers of Trima Accel(R) are an excellent alternative source of viable and functional human blood cells, which can be used for research purposes.