An adsorbent material intended particularly for use in extracorporeal haemodialysis, is described which is composed of granules of an adsorbent which are coated with a biocompatible polymeric membrane which is semipermeable to the solutes selected for removal. The polymer is a copolymer containing carboxyl and amino groups. In use, solutes pass selectively through the membrane and are trapped by adsorption in the adsorbent thereby preventing or at least reducing the reverse process. To improve biocompatibility the product may be further coated with a plasma protein.