In this work, we describe the reduction of O-2, CO2 and N2O, in the presence of each other, at an unshielded gold microdisc electrode, in dimethylsulfoxide (DMSO) as the solvent and with a Ag quasi-reference electrode. Carbon dioxide and nitrous oxide, when present on their own in N-2, have been shown previously to be reduced at very similar potentials. So, it was not necessarily anticipated that gas mixtures containing both these two gases could be determined analytically. However, remarkably, a well resolved new CO, wave, which was ideal for analytical purposes, was observed under our experimental conditions in the presence of O-2 and N2O. Furthermore, and most importantly, no cross-interference from the O-2, N2O, and the new CO2 reactions, was evident when the N,O concentration was in excess of that of CO2 (the normal anaesthetic expired gas and blood gas analysis situation). The O-2, CO2 and N2O concentrations were determined from the limiting currents of the well-separated waves.