A major problem with the use of umbilical cord/placental blood (UCB) is the limited blood volume that can be collected from a single donor. In this study, we evaluated a novel system for the collection of UCB and analyzed the kinetics of output of hematopoietic stem cells in the collected blood. Sequential UCB fractions were collected from 48 placentas by gravity following common procedures. When UCB flow was ended, collection was continued using the device. Nucleated cell (NC) density in each fraction was evaluated and the expression of CD34, CD38 and other hematopoietic markers was assessed by flow cytometry. The total collected volume was 60.9 +/- 26.2 ml (mean +/- SD, range 17-141.5). The device yield (volume collected using the device/total volume) was 26.5 +/- 15.1%. No significant difference was observed in NC count in sequential fractions. A significant increase in CD34(+) cell content in sequential fractions and a 2.07 +/- 1.18-fold increase in the percentage of CD34(+) cells in the last versus first fraction were observed. Furthermore, within the CD34(+) population, the percentage of CD38(-) pluripotent stem cells in the first fraction was 3.24 +/- 1.39, while in the last fraction it raised to 34.43 +/- 22.62. Thus, at the end of a collection performed following current procedures, further blood rich in the most primitive progenitor cells can be recovered. Therefore, the optimization and standardization of collection procedures are required to obtain maximal recovery from each placenta and increase the percentage of UCB units suitable for clinical use.