The present paper outlines the methods used to reduce the interference signal caused by ascorbic and uric acids on an ammonia amperometric sensor in aqueous solutions. The sensor was prepared by electrochemical deposition of poly(pyrrole), doped with dodecylbenzenesulfonic anions (DBS), onto platinum substrates. Poly(pyrrole) films were coated with different membranes, aiming to find different ways to diminish the interference response of anionic species such as ascorbate and urate. Nafion((R)), cellulose acetate and poly(5-amino-1-naphthol), were studied as permselective layers. This last polymer is electroactive, offering the possibility of its formation by electrochemical deposition onto poly(pyrrole). In order to verify the stability of poly(5-amino-1-naphthol) when used in basic medium, Raman spectra were taken from these modified electrodes. Further, all sensors showed a linear response and a good sensitivity in a concentration range from 0 to 120 mumol L-1 which covers the ammonia concentration range typical of clinical samples (18-72 mumol L-1). (C) 2004 Elsevier Ltd. All rights reserved.