This work reports the electrocatalytic activity of 2,3,5,6-tetrachloro-1,4-benzoquinone (TCBQ)/multi-walled carbon nanotubes (MWCNT) immobilized on an edge plane pyrolytic graphite electrode for nicotinamide adenine dinucleotide (NADH) oxidation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) were used to confirms the presence of chloro after the nanotube modification with 2,3,5,6-tetrachloro-1,4-benzoqui none. The surface charge transfer constant, k(s), and the charge transfer coefficient for the modified electrode, alpha, were estimated as 98.5 (+/- 0.6) s(-1) and 0.5, respectively. With this modified electrode the oxidation potential of the NADH was shifted about 300 mV toward a less positive value, presenting a peak current much higher than those measured on an unmodified edge plane pyrolytic graphite electrode (EPPG). Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the NADH oxidation reaction involves 2 electrons and a heterogenous rate constant (k(obs)) of 3.1 x 10(5) mol(-1) l s(-1). The detection limit, repeatability, long-term stability, time of response and linear response range were also investigated. (C) 2008 Elsevier Ltd. All rights reserved.