The electrochemical behaviour of nitric oxide (NO) at a glassy carbon electrode modified by a thin layer of electrodeposited molybdenum oxide has been examined in phosphate buffer (pH 7.4). The data show that the anodic current for the oxidation of NO is increased greatly when the process occurs at the modified surface and a possible explanation would involve the O-atom transfer from the MoO3 film to the substrate by an inner-sphere mechanism. The accumulation of NO in the pores of the film by a kind of chemical interaction was also investigated, and may be in part responsible for the current enhancement observed when the substrate is oxidised anodically at the modified electrode.