The formation of oxidation products of NAD(+), which catalyses the NADH oxidation, depends on the electrode material employed. Carbon paste electrodes with various pasting liquids and with various pasting liquid/graphite ratios are examined using cyclic voltammetry and amperometric measurements. A qualitative model of the carbon paste electrode is discussed that assumes the existence of surface sites in contact with aqueous media and pasting liquid. Vitreous carbon, reticulated vitreous carbon, pyrolitic graphite and platinum are also used as working electrodes. Anodic pretreatment increases the catalytic current for NADH oxidation associated with the oxidation products of NAD(+). This is due to an increase in the surface area during pretreatment, which produces an increased number of surface sites in contact with aqueous media and pasting liquid. NAD(+) incorporated into the paste itself results in adsorbed species being strongly attached to the carbon paste surface. The apparent rate constant of the electrochemical reaction is found to be 8.5 s(-1).