The oxidation of nicotinic acid and nicotinamide on a polycrystalline gold electrode occurred at almost same potentials but their reduction did at different peak potentials. The redox reaction mechanisms of nicotinic acid and nicotinamide were rationalized by the formation/disappearance of the new nitrogen-oxygen bonds in the pyridine rings by means of cyclic voltammetry and bulk electrolysis. The anodic currents of nicotinic acid and nicotinamide were controlled by diffusion, while the cathodic ones by adsorption. The difference in the cathodic peak potentials of nicotinic acid and nicotinamide on the polycrystalline gold electrode is attributed to the effect of the electron densities of remote substituents on the pyridine rings. The cathodic peak currents at about 0.20 V were linear with their concentrations in the range of 2.4 mM to 2.7 mu M and 2.4 mM to 3.3 mu M with detection limits of 0.27 and 0.33 mu M for nicotinic acid and nicotinamide, respectively. Voltammetry was then adopted for the selective monitoring the content of nicotinic acid and nicotinamide in pharmaceuticals. (c) 2006 Elsevier Ltd. All rights reserved.