Infrared derivative spectroscopy using a tunable diode laser coupled to a multipass absorption cell has been used to measure the nitrous oxide mole fraction in tropospheric air samples. The individual measurement precision was 1.5% (1&sgr;). No temporal variation outside the statistical error limits was observed in 26 measurements over a two month period. Absolute values were obtained by comparison to manometrically calibrated standards prepared by static dilutions of N2O in air to ambient levels. The mean mole fraction of N2O in dry air was determined to be 298¿5 ppb where the error includes an estimate of possible systematic errors in standard preparation.