AbstractPlasma exchange (PE) is performed only rarely to remove a specific, well defined antibody. ABO incompatibility in marrow transplantation has allowed us a unique opportunity to compare the effectiveness of three apheresis procedures for removing anti‐red cell antibodies. We performed 140 marrow transplants in which a major ABO incompatibility between donor and recipient existed. To avoid a hemolytic transfusion reaction at the time of marrow infusion PE, plasma immunoadsorption (PIA) or whole‐blood immunoadsorption (WBIA) was performed a total of 243 times. PE removed a mean of 87% of intravascular IgM and 86% of intravascular IgG directed against red cell antigens. PIA removed 75% and 73% of IgM and IgG, respectively (P<.001 when compared to PE). Results for WBIA were 66% and 65%, respectively. Thus, PIA and WBIA were less efficient at removing antibody than PE. Furthermore, there were a few specific instances in which PIA or WBIA removed little or no antibody owing to differences in antibody specificity. PIA and WBIA resulted in less platelet consumption than PE. Although somewhat less effective that PE, PIA and WBIA have other advantages that can make them more desira