A novel poly(N-isopropylacrylamide) (PNIPA)/PNIPA interpenetrating polymer network (IPN) was synthesized and characterized. In comparison with conventional PNIPA hydrogels, the shrinking rate of the IPN hydrogel increased when gels, swollen at 20 degreesC, were immersed. in 50 degreesC water. The phase-transition temperature of the IPN gel remained unchangeable because of the same chemical constituent in the PNIPA gel. The reswelling kinetics were slower than those of the PNIPA hydrogel because of the higher crosslinking density of the IPN hydrogel. The IPN hydrogel had better mechanical strength because of its higher crosslinking density and polymer volume fraction. The release behavior of 5-fluorouracil (5-Fu) from the IPN hydrogel showed that, at a lower temperature, the release of 5-Fu was controlled by the diffusion of water molecules in the gel network. At a higher temperature, 5-Fu inside the gel could not diffuse into the medium after a burst release caused by the release of the drug on the surface of the gel. (C) 2004 Wiley Periodicals, Inc.