Leukocytapheresis has long been performed with the centrifugal method. But in 1989 in Japan, the Asahi Medical Co. developed the extracorporeal leukocyte-removal filter, Cellsorba. This filter consists of non-woven fabric, which can remove leukocytes from whole blood during extracorporeal circulation. In the incipient stage, this filter was applied to collagen diseases, rheumatoid arthritis, and systemic lupus erythematosus. During the following studies, this filter has been found to have an immunosuppressive effect. Now, it is beginning to be applied to various kinds of autoimmune diseases. Moreover, this filter has recently been recognized to be effective in inflammatory bowel diseases, ulcerative colitis, and Crohn's disease. The outline of Cellsorba and the application of this filter is described here.