Efficient cell separation is important for the successful isolation and purification of blood cells, stem cells, and specific tissue cells. Cell separation through membrane filtration was recently reported by several researchers. Leukocyte removal filters are commercially available cell separation filters. Removal of leukocytes from the blood using these filters has successfully decreased the side effects of blood transfusions and viral infections arising from leukocytes in donor blood. Compared with other cell separation methods, membrane filtration is simple and inexpensive, and sterility is easy to maintain during the process.