The aim of this work is the study of the electrochemical behaviour of methanol and CO electro-oxidation reaction with amorphous metallic alloys of compositions (NiNb)(99)(PtX)(1) (X = Ru, Sn, compositions in at.%), which are obtained by mechanical alloying, that results to in powders used as modified carbon paste electrodes (MCPEs). The presence of tin drastically decreases the reactivity towards methanol electro-oxidation of the alloy, followed by the Ni59Nb40Pt1 and Ni59Nb40Pt0.6Ru0.4 alloys. Differential electrochemical mass spectrometry (DEMS) studies demonstrate that the Ni59Nb40Pt0.6Ru0.4 and Ni59Nb40Pt0.6Sn0.4 electrodes show the best tolerance to CO produced by methanol deprotonation, giving rise to more negative onset potential values for the CO2 production, although the voltammograms for the stripping of a CO monolayer clearly show that the electrode that possesses a better tolerance to CO adsorbed on the surface of the electrode is Ni59Nb40Pt0.6Sn0.4, decreasing the onset potential values 281 and 158 mV with regard to the Ni59Nb40Pt1 and Ni59Nb40Pt0.6Ru0.4, respectively. The catalytic activity of the electrode formed might be attributed to an adsorbed state of CO unique in this alloy. (c) 2007 Elsevier B.V. All rights reserved.