Polyamphoteric hydrogel membranes were synthesized by graft copolymerization of N-isopropylacrylamide (NIPAm) and 2-acrylamido-2-methyl propane sulfonic acid (AMPS) onto chitosan (CS). The incorporation of poly(NIPAm) (PNIPAm) and poly(AMPS) (PAMPS) into CS was confirmed by FTIR spectroscopy. The swelling behavior of membranes as a function of pH, temperature, and ionic strength was studied. Permeability of solutes through these membranes was investigated at different temperatures. The results showed the dual sensitivity of membranes toward pH and temperature. The formation of the polyelectrolyte complex between CS and PAMPS showed influence on the lower critical solution temperature of PNIPAm. The permeabilities of solutes through these membranes were strongly dependent on the size of solutes, solution temperature, and hydrophilicity of the membranes. (C) 2004 Wiley Periodicals, Inc.