Poly(N-isopropylacrylamide-co-maleic acid)zinc oxide [P(NIPA/MA)/ZnO] composite hydrogels, containing a definite amount of ZnO, were prepared from N-isopropylacrylamide (NIPA) and maleic acid (MA) monomers with 0-31.15 mol % MA in aqueous saturated zinc oxide solutions by radiation-induced polymerization and gelation using gamma rays from a Co-60 source. The amounts of released ZnO from these composite hydrogels were determined by differential pulse polarography (DPP) using the characteristic peaks obtained at about -1,000, -1,050, and -1,300 mV at pH 2.0, 5.5, and 7.05, respectively. It was found that the ZnO-release behavior of P(NIPA/MA)/ZnO composite hydrogels depended strongly on the MA content and pH of the medium. (C) 2004 Wiley Periodicals, Inc.