We report in this study, and for the first time the direct and simultaneous electrochemical measurements of both nitric oxide and superoxide anion evolution and reactivity in solution. For this purpose, we have combined the use of two electrodes : a previously developed NO-sensor for the amperometric determination of NO and a carbon microelectrode for the amperometric detection of superoxide anion. The latter electrode displayed a potential use for the selective detection of O-2(-) (generated by the xanthine/xanthine oxidase reaction) with an acceptable selectivity against uric acid. Our electrochemical experiments were validated by the Cytochrome c method and by the use of a different procedure for the generation of the superoxide anions. Our results show that the use of the NO sensor provides the selective detection of NO without any interference of the superoxide enzymatic generator.