the invention relates to methods for separating biological contaminants from biological products , or for reducing the content of such biological contaminants in said biological products . the sample to be purified is treated with an anion exchanger membrane . said anion exchanger membrane is obtained by reacting a polyamide with an aminoreactive compound which is capable of polymerisation . this is followed by polymerisation with monomers which contain cationic groups or into which cationic groups can be introduced in a reaction analogous to polymerisation .