Abstract: A chemically active membrane having a large surface area is provided in which a hydrophilic, microporous, skinless, polyamide membrane is chemically bound to a residue of an activating agent which is capable of reacting with a biologically active material.The chemically active membrane, formed by reacting a hydrophilic, microporous, skinless, polyamide membrane with an activating agent may be used to prepare a biologically active membrane having a large surface area which comprises an acceptor molecule such as a monoclonal antibody, a polyclonal antibody, an antigenic substance, a glycoprotein, Protein A, a lectin, a carbohydrate, an enzyme substrate, a cofactor, an inhibitor, a hormone, an IgG class of immunoglobulin, a carrier protein, a receptor, heparin, a coagulation factor, or a histone covalently bound to the hydrophilic, microporous, skinless, polyamide membrane by reacting the chemically activate membrane with the acceptor molecule.