Four different polypyrrole/polytetrahydrofuran/invertase electrodes were constructed by the entrapment of invertase in conducting polymer matrices via electropolymerization. Immobilization of the enzyme was achieved by the application of a 1.1 V constant potential to a platinum electrode for 30 min in a solution containing 0.01 M pyrrole, 0.4 mg/ml invertase and 0.4 mg/ml sodium dodecyl sulphate. Performance of each electrode was optimized by examining the effects of pH and temperature on the properties of the electrodes. The changes in the maximum velocity of the reaction and variation of Michaelis-Menten constant upon immobilization were investigated. The enzyme immobilized in those matrices retained its activity for several months. (C) 1999 Elsevier Science S.A. All rights reserved.