Cell separation from peripheral blood was investigated using surface-modified polyurethane (PU) membranes with different functional groups. Both red blood cells and platelets could pass through unmodified PU and PU-SO 3 H membranes, whereas the red blood cells preferentially passed through PU-N(C 2 H 5 ) 2 and PU-NHC 2 H 4 OH membranes. The permeation ratio of T and B cells was Ͻ25% for the surface-modified and unmodified PU membranes. CD34 ϩ cells have been recognized as various kinds of stem cells including hematopoietic and mesenchymal stem cells. The adhesiveness of CD34 ϩ cells on the PU membranes was found to be higher than that of red blood cells, platelets, T cells, or B cells. Overall, the adhesiveness of blood cells on the PU membranes increased in the following order: red blood cells Յ platelets Ͻ T cells Յ B cells Ͻ CD34 ϩ cells. Treatment of PU-COOH membranes with a human albumin solution to detach adhered blood cells, allowed recovery of mainly CD34 ϩ cells in the permeate, whereas both red blood cells and platelets could be isolated in the permeate using unmodified PU membranes. The PU membranes showed different permeation and recovery ratios of specific cells depending on the functional groups attached to the membranes.