A novel polymeric lead(II) adsorbent is prepared by incorporating benzo-18-crown-6-acrylamide (BCAm) as metal ion receptor into the thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel. Both stimuli-sensitive properties and the Pb2+-adsorption capabilities of the prepared P(NIPAM-co-BCAm) hydrogels are investigated. The prepared P(NIPAM-co-BCAm) hydrogels exhibit good ion-recognition and Pb2+-adsorption characteristics. When crown ether units capture Pb2+ and form BCAm/Pb2+ host-guest complexes, the lower critical solution temperature (LCST) of the hydrogel shifts to a higher temperature due to both the repulsion among charged BCAm/Pb2+ groups and the osmotic pressure within the hydrogel. The adsorption results at different temperatures show that P(NIPAM-co-BCAm) hydrogels adsorb Pb2+ ions at temperature lower than the LCST, but undergo desorption at temperature higher than the LCST due to the "stretch-to-shrink" configuration change of copolymer networks which is triggered by the change in environmental temperature. This kind of ion-recognition hydrogel is promising as a novel adsorption material for adsorption and separation of Pb2+ ions. The adsorption and desorption of Pb2+ could be rationally achieved by simply changing the environmental temperature. (C) 2008 Elsevier B.V. All rights reserved.