The amperometric ammonia determination by use of a polyaniline-modified screen printed Pt–C electrode at 0.3 V (versus Ag/AgCl on the strip) is shown. The electrochemical pulse polarization method is used for the modification. The effects of basic electrode material, applied potential, pH of buffer solution and possible interferences of other ions were studied. The polyaniline-modified Pt–C electrode measures (NH₄)₂SO₄ with a detection limit of 5 μM, a linear range up to 1 mM and a sensitivity of 40 ± 20 μA cm⁻² mM⁻¹. A new generation of enzyme sensors arises from the immobilization of ammonia-forming enzymes in a poly(carbamoyl)sulphonate hydrogel matrix on the working electrode as it is shown for urease to detect urea.