A novel potentiometric biosensor for urea, based on the entrapment of urease into a polypyrrole film, has been developed via galavanostatic film formation. The electrochemical polymerization was achieved by the application of a current density of 0.5 mA cm-2 to a working platinum disc electrode for 3 min in a solution containing 0.5 M pyrrole and 4000 μ ml-1 urease. The optimum conditions for the reliable performance of this sensor were 1 mM phosphate buffer at pH 7.0 and 35°C. A Nerstein response was observed for increasing concentration of urea in the linear range of 0.5 to 100mM. Trace concentrations of Hg2+ and K+ were both found to inhibit the response of the biosensor.