Abstract: An adsorbent that comprises a solid phase for the isolation and immobilization of proteins by adsorption from a liquid phase is characterized in that it consists of a hydrophilic polymer network with covalently bound ligands of the formula--Y--X--R,in which R is an aliphatic substituent containing at least one nitrile group or a substituent having a heterocyclic ring system with at least one nitrogen atom in the ring and with one or more side groups consisting of or including --CN (nitrile group), whereX is NQ, S, or O, Q being H(CH.sub.2).sub.n, where n=0, 1, 2 or 3, andY is a side chain which joins R-X with the polymer network.The polymer preferably consists of agar or agarose in particle form having a particle size of <1 mm. Y can be --CH.sub.2 --CH.sub.2 SO.sub.2 --CH.sub.2 --CH.sub.2 -- and R can be ##STR1## The adsorbent can be used to isolate biopolymers and, inter alia, has been found highly effective in isolating proteins.