A description of a new chemiluminescent balloon sonde for measuring stratospheric nitric oxide is given. First results from three flights at mid-latitudes are presented, including measurements showing a slow reduction in NO mixing ratio beginning 2 1/2 hours before sunset. A hysteresis in the NO mixing ratio between ascent in the morning and descent in the afternoon was observed. The afternoon values were found to be up to a factor of 2 larger than the morning values.