A novel flow injection amperometric urea biosensor, based on the incorporation of urease into a conductive polypyrrole film, has been developed. The amperometric detection of as little as 3 ppm of urea by flow injection analysis (FIA) was accomplished in 0.05 M phosphate buffer (pH 7.0) with the application of an electrode potential of -70 mV vs, Ag/AgCl to the biosensor, Optimum interaction between urea and the immobilized enzyme was accomplished by use of a relatively slow flow-rate of 0.1 ml/min. Under these conditions, the amperometric response was linear between 3 and 15 mg/l. Potential interferants such as potassium nitrate and potassium chloride did not have any effect on the biosensor when present up to 0.01 M, but ammonia and ammonium ions gave similar response to that of urea. This observation confirms that the biocatalytic reaction product contained either ammonia or ammonium ions.