Urease was immobilized in conducting polypyrrole and block copolymers of thiophene-capped poly(methyl methacrylate) matrices by electropolymerization. Immobilization of the enzyme was achieved by application of 1.0 V constant potential in a solution of 0.02 M pyrrole, 2 mg/ml urease, 0.5 mg/ml supporting electrolyte. The optimum immobilization conditions, electrolysis time, electrolysis medium, enzyme concentration during electrolysis, type of supporting electrolyte were determined. The kinetic behaviors of free and immobilized urease were determined. (C) 2001 Elsevier Science B.V. All rights reserved.