Multiple administration of the generally called immunosuppressing agents is the usual fashion for suppressing/ameliorating the rejection reaction that inevitably occurs after organ allotransplantation. Although a definite mechanism of the rejection reaction has not been elucidated, evidence has accumulated that cellular components, such as T- and B-lymphocytes, and humoral factors, such as antibodies and immune complexes, play a certain role. There also is a possibility that direct removal or functional revolution of those components and/or factors utilizing an extracorporeal procedure influence an immune mechanism of the rejection reaction. Some of the extracorporeal procedures, which have been developed from blood purification techniques, have been evidenced to modify an immune mechanism and, as a result, bring about better graft function to a considerable extent that may not be otherwise achieved by traditional immunosuppressant treatment. The term "extracorporeal immunomodulation" was given to such extracorporeal procedures.