Abstract: An affinity support is provided containing a high flux semipermeable hydrogel membrane surface-modified with an affinity ligand, such as a protein which may be an antibody or enzyme, or a cell receptor complement, useful for affinity separation of biological macromolecules, including insoluble proteins, cells, and cell fragments, from solution. The exclusion limit (molecular weight cut-off) of the matrix is selected to substantially restrict immobilized protein or other ligand to the surface thereof for maximization of available ligand binding capacity. The exclusion limit is also selected to permit reagent(s) used for the matrix/ligand linkage to penetrate into and form covalent bonds with the membrane on the interior surfaces of the membrane for optimizing packing densities of the affinity ligand exterior to the membrane.