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 (2&sgr; 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 calculations.