The separation of hematopoietic stem and progenitor cells (CD34(+) cells) from peripheral blood was investigated using foamed polyurethane (PU) membranes modified with several amino acids. CD34(+) cells were collected by first allowing the blood to permeate through the membranes, and then passing the recovered solution through the membranes. Optimal conditions for the separation of CD34(+) cells were investigated. The highest recovery ratio of CD34(+) cells was obtained using three sheets of PU membranes having carboxylic acid groups (PU-COOH) modified with glycine, the membranes having been pretreated by immersion in phosphate buffer solution prior to permeation of blood. A high recovery ratio of CD34(+) cells was achieved in a recovery process using 0.5 wt % human serum albumin (HSA) or 20% dextran solution passed through PU-COOH membranes. The recovery ratios of CD34(+) cells using platelet-poor plasma and platelet-rich plasma were approximately 20% and 30%, respectively, significantly less than the ratio found using 0.5 wt % HSA solution. Surface-modified membranes having carboxylic acid groups showed a higher recovery ratio of CD34(+) cells than membranes having zwitterionic groups. The effect of carboxylic acid groups on the surface-modified PU membranes was to generate weak interactions by electrostatic repulsion between CD34(+) cells and the membranes because of the negatively charged surfaces of the cells, allowing them to be detached from the membranes and collected in the recovered solution. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 671-679, 2009