A glassy carbon electrode modified with silver nanoparticles was employed as a nitrate sensor to give a calibration curve with a sensitivity of 2.6 mu A mu M-1 cm(-2) and a LOD of 4.1 mu M NO3- at a neutral pH. The calibration curve was generated using rotating disc voltammetry coupled with constant potential amperometry, giving efficient diffusion of the nitrate to the surface. Reasonably good selectivity for nitrate was observed in the presence of nitrite, chloride and phosphate anions. The nitrate diffusion coefficient was estimated as 1.41 x 10(-5) to 1.73 x 10(-5) cm(2) s(-1) using a combination of cyclic voltammetry and rotating disc voltammetry, while the rate constant for the nitrate reduction reaction was estimated as 0.11 cm s(-1). Some deviations from the Randles-Sevick and Levich equations were seen at higher scan rates, consistent with the slow kinetics and nitrate adsorption. While stable silver nanoparticles were electrochemically formed in the solution phase and incorporated within a hydrogel matrix, the best approach in forming the nitrate sensor was the direct electrodeposition of silver nanoparticles at glassy carbon at - 0.50 V versus Ag|Ag+ following a 60-min seeding period at the open-circuit potential. [GRAPHICS] .