A series of thermo- and pH-sensitive poly (N,N-diethylacrylamide-co-acrylic acid) (P(DEA-co-AA)) hydrogels were prepared in NaCl aqueous solutions with different concentrations. Swelling and deswelling studies showed that in comparison with conventional P(DEA-coAA) hydrogels (prepared in distilled water), the P(DEA-coAA) hydrogels thus prepared had almost the same volume phase transition temperature (VPTT), but exhibited much faster response rates as the temperature was raised above their VPTT. Besides, the hydrogels prepared by this method had faster response rates in low pH buffer solutions, and the response rates increased with the increased concentration of the NaCl solutions used during the polymerization. (c) 2008 Wiley Periodicals, Inc.