A hydrophilic, water-insoluble polymer was prepared, starting from commercial poly(vinyl alcohol) that was crosslinked and functionalized by means of glutaraldehyde and 4-nitrobenzaldehyde. The resulting beads were then reduced and subsequently diazotized, and finally contained diazonium moieties capable of covalently coupling with electron-rich aromatic systems such as histidine and/or tyrosine residues of proteins. The described resin is therefore well suitable for protein immobilization whenever lysine residues (those involved in covalent coupling with several popular immobilization procedures) are not available and/or cannot be used unless the biological activity of the protein is destroyed.