This is a microchromatographic method for simultaneous determinations of O2, N2, CO2 and N2O in gas samples of 40–100μl. A Packard 836 U gas chromatograph with a thermal conductivity detector and helium gas as carrier was used. The combination of Porapak® and 5A molecular sieve column system was found adequate and is described in detail. The fidelity of this method was proved by a high constancy of the retention time, the linearity of the response and the reproducibility of results. The present method proved to be reliable for determination of all middle ear gases in man and experimental animals during general anesthesia with N2O.