Polyelectrolyte Poly(N-vinyl-2-pyrrolidone-co-itaconic acid) hydrogels (P(VP/IA)) with varying compositions were prepared from ternary VP/IA/water mixtures. The effect of external stimuli such as pH of the solution, temperature, substrate concentration of solution, and storage stability on the invertase adsorption capacity of P(VP/IA) hydrogels was investigated. The adsorption capacity of the hydrogels was found to increase from 4.4 to 18.4 mg invertase/g dry gel with increasing amount of IA in the gel system, while P(VP) gel adsorbed only 3.1 mg invertase/g dry gel. Kinetic parameters were calculated as Michaelis-Menten constant K-m = 20.6 mmoI L-1 and maximum velocity V-max = 6.44 x 10(-5) mol dm(-3) min(-1) for free enzyme and in the range of K-m = 26.4 -41.1 mmol L-1 and V-max = 6.35.10(-5)-6.66.10(-5) mol dm(-3) min(-1), depending on the amount of IA in the hydrogel. Enzyme activities were found to increase from 59.0% to 72.0% with increasing amount of IA in the gel system and retained their activities for one month storage. The enzyme activities, after storage for one month at 4 degrees C, were found to be 21.0% and 59.0-74.0% of the initial activity values for free and adsorbed enzyme, respectively The optimal pH values for free and adsorbed enzymes were determined as 4.56 and 5.00, respectively. The optimum temperature for free and adsorbed enzymes was 55 degrees C. Adsorption studies have shown that not only the gel composition but also the stimuli, temperature and pH of the solution play an important role on the invertase adsorption capacity of poly(VP/IA) hydrogels.