In two previous papers we described : (a) the reduction of O-2 and CO2, in the presence of each other, in an aprotic solvent with minimal cross-interference between the competing O-2 and CO2 reduction reactions; (b) a practical Clark-type membrane-covered sensor for the simultaneous measurement of O-2 and CO2. The sensor comprised a gold disc microelectrode, housed in a PTFE herder and covered with a PTFE membrane, with dimethyl sulphoxide as the solvent and with an Ag quasi-reference electrode. In this new work, we describe the reduction of O-2 and N2O, in the presence of each other, with this same sensor when the microelectrode was first unshielded and then membrane-covered. No cross-interference from the two reactions was evident, and the problem of N-2 bubble build-up on the microelectrode surface, from the reduction of N2O, was minimised by sweeping the polarising voltage from 0 to -2.4 V (Ag) at a typical sweep rate of 0.1 to 0.5 V s(-1). The O-2 and N2O concentrations were determined from the limiting currents of the well-separated O-2 and reduction N2O waves. We also demonstrated that the addition of up to 10% v/v H2O to the solvent did not appear to compromise the ability of the sensor to analyse O-2 and N2O simultaneously.