A balloon‐borne experiment to measure midlatitude stratospheric [BrO] and [ClO]by NO chemical conversion/atomic resonance fluorescence was flown from Palestine, Texas, on 20 May 1986. In this first study of BrO, no signal attributable to BrO was detected, and upper limits (2σ uncertainty) between 35 and 24 km altitude give BrO mixing ratios less than 15 pptv. Current models predict mixing ratios that are 1.7 times larger. Measurements of [ClO] were obtained at less than .2 km altitude resolution from 41 to 22 km. The smoothly varying altitude profile lies within the range of 2‐D model calculat