The noncovalent immobilization of enzymes such as alpha-amylase, beta-glucosidase, trypsin, and alkaline phosphatase was performed by adsorption on the water-soluble polymer Eudragit S-100. The strength of the binding with enzymes in some cases was critically dependent upon the initial polymer concentration used during binding. In all the cases tried, a moder-ate increase in polymer concentration ensured adequate immobilization of enzymes. The immobilized enzymes retained different activities : 87, 59, 49, and 24% for beta-glucosidase, alpha-amylase, trypsin, and alkaline phosphatase, respectively. The K-m value of immobilized enzyme was the same as that of native enzyme for beta-glucosidase (3.8 x 10(-3) M) and alpha-amylase (6 mg ml(-1)) whereas the K, value decreased in the case of trypsin (from 1 x 10(-3) M to 0.6 x 10(-3) M) upon immobilization. The immobilized trypsin showed improved stability to autolysis at 35 degrees C whereas immobilization resulted in a decrease in the thermal stability of alpha-amylase at 50 degrees C. No significant changes were observed in pH optimum of the enzymes upon immobilization. U.V. and fluorescence emission spectra of immobilized trypsin reflected the conformational changes which enzymes undergo upon adsorption on the polymer.