Abstract: A polymeric gel in which salicylaldehyde and lysine moieties are capable of forming an internal aldimine at pH > 6,0 has been prepared by copolymerization of N-5-methacryloylaminosalicylidene-N-methacryloyl-(S)-lysinatocopper (II) (1a) with acrylamide and N,N'-methylenebisacrylamide in water with subsequent removal of the copper ions by 0,1 M HCl or the disodium salt of EDTA. The equilibrium formation constants of the internal aldimine are ca. 30 times (at pH 7,1) and ca. 100 times (at pH 9,2) higher than the equilibrium constants of the model reaction of Schiff base formation from 5-isobutyrylaminosalicylaldehyde (2) and Nt-isobutyryl-(S)-lysine (3). The -amino group of the lysine residue in the gel acts as a nucleophilic catalyst in the reaction of the salicylaldehyde moiety of the gel with semicarbazide. The reaction proceeds 5,3 times faster in the gel than in a model polymeric system which does not contain lysine moieties.