Hyperacute rejection following xenogeneic transplantation in primates is mediated by naturally occurring IgM antibodies, which are specifically directed to alpha-Galactosyl residues on many nonprimate mammalian cells. Current approaches to remove these anti-alphaGal IgM include plasmapheresis followed by immunoaffinity adsorption on bead columns using synthetic Gal epitopes, which requires two pieces of complex equipment. In this study, we explored the use of immunoaffinity adsorption with hollow fiber microporous or dialysis membranes to which a synthetic alphaGal trisaccharide ligand is bound. Covalent attachment of ligand directly to the surface produced negligible binding, but use of long-chain polyamines as reactive spacers yielded binding densities for anti-alphaGal IgM as high as 89 mg/mL membrane volume in breakthrough curve experiments with microporous nylon membranes having an internal surface area of 4.2 m(2)/mL membrane volume. A crossflow microfilter fabricated from the membranes described in this study and having about 0.4 m(2) luminal surface area would be able to carry out plasma separation and immunoadsorption in a single device with a large excess of binding capacity to ensure that all plasma that filters across the device and is returned to a human patient is essentially free of anti-alphaGal IgM. We conclude that immunoaffinity removal of xenoreactive antibodies using microfiltration hollow fiber membranes is feasible and has potential advantages of efficiency and simplicity for clinical application.