The total odd nitrogen mixing ratio experiment has been conducted successfully for a second time on a balloon flight of PROJECT STRATOPROBE launched on August 17, 1975 from 51¿N. The measured NOy profile was found to be similar to the first profile measurement from 58¿N on July 22, 1974 with a maximum mixing ratio of 13 ppbv at 32 km decreasing at lower altitudes to less than 2 ppbv at 16 km. This result was not unexpected, since the ozone mixing ratio profile was similar on both flight dates. Both measurement sets were carried out at mid latitudes during late summer, an excellent time for measurements of ozone layer photochemistry since the ozone layer is very stable during this season.