The first measurement of the hemispheric distribution of N2O concentrations in the lower stratosphere of the Northern Hemisphere is reported for July 1975. This distribution is similar to those of CCl3F and SF6, although N2O is more stable in the stratosphere than either of the other trace gases. The inventory of N2O in the stratosphere of the Northern Hemisphere in July 1975 against which future observations can be compared is 136 Tg.