Modification of polystyrene for higher binding capacity and/or for specific covalent immobilization of biomolecules is discussed. The benefit of covalent coupling of biomolecules onto a new commercially available surface type for covalent immobilization, CovaLink NH, is illustrated. The CovaLink NH solid phase has spacer arms covalently grafted onto the polystyrene solid phase, approximately 10(14) groups/cm2. Coupling procedures for covalent immobilization of biotin and peptides are demonstrated, and the advantage of using carbodiimide for coupling of carboxylic acid containing compounds is shown.