Seventy-five ground level and six parachute descent grab samples of tropospheric air have been made at a variety of locations throughout the world over a 6-month period. The N2O mixing ratios in the samples have been determined by electron capture gas chromatography to an absolute accuracy of about 5% an estimate that is based on the results of several interlaboratory comparisons of calibration standards. The mean ground level N2O mixing ratio from these measurements was 326 ppbv (parts per billion by volume), referenced to 'dry air,' and was found to be remarkably constant. The residual standard deviation was 5.3 ppbv. This worldwide mean is consistent with other recent measurements but is considerably larger than many of the earlier measurements. The present data indicate that the N2O residence time in the troposphere is very likely to be greater than 11 years. Furthermore, the data separately show that the possibility of a current annual increase in the N2O mixing ratio by more than 4% seems to be excluded. The parachute descent data, taken just below the tropopause, have a slightly smaller mean, 318 ppbv, but support the contention that the present tropospheric N2O mixing ratio is well above 300 ppbv.