Results from the first continuous program for studying atmospheric nitrous oxide (N2O) in the southern hemisphere are presented. Daily measurements at Aspendale, Australia (38.1¿ S, 145.2¿ E), yield an average N2O mixing ratio of 340 ppb in dry air for the period October 1976 to May 1978. No significant long-term trend has been detected. Analysis of air collected at several clean air (marine and rural) locations reveals a significantly lower mixing rato of 337--338 ppb. The difference is attributed to an urban source of N2O. Results from an extensive air sampling network illustrate the homogeneous distribution of N2O in the troposphere and reveal no variations in mixing ratio which could be attributable to seasonal or synoptic variations. The N2O mixing ratio decreases above the tropopause. Preliminary results of the direct measurement of N2O exhalation from soil are reported. Both the constancy of the N2O mixing ratio in the troposphere and the low exhalation rates from soil suggest a long lifetime for N2O in the atmosphere. This implies small sources and sinks and makes the atmospheric N2O cycle susceptible to anthropogenic inputs. All measurements were made by electron capture gas chromatography with a precision of approximately 1%. The uncertainty in the absolute value of the N2O mixing ratio is 10--15%. The need for accurate and reproducible gas standards and for regular interlaboratory comparisons of standard is discussed.