The electrocatalytic activity of various adsorbed metallophthalocyanines (M-Pc) on vitreous carbon electrode for the oxidation of nitric oxide has been investigated in an aqueous phosphate buffer solution (pH 7.3). When comparing phthalocyanines of different metals, the influence of the nature of the metal on the activity is not very strong. For the most active complex, Ni-Pc, the reaction rate is only four times higher than that for Cu-Pc, the least active one. The effect of substituents on the periphery of the phthalocyanine ligand is slightly more pronounced. In the case of the nickel complexes, electron-withdrawing substituents on the periphery of the phthalocyanine ligand enhance this activity. This is due to the decrease of the electron density on the nickel center, facilitating the formation of NO+ species in the rate-determining step. (C) 2003 The Electrochemical Society.