An upper limit on the yield of HBr from reaction (R1) (HO2+BrO→products) has been determined by measuring an upper limit for the rate coefficient of the reverse (R-1) (HBr+O3→HO2+BrO). The limits measured at 300 and 441 K were extrapolated to low temperatures to determine that the yield of HBr from reaction (R1) is negligible throughout the stratosphere (<0.01% of k1). An upper limit for the rate coefficient of the reaction of HO2 with HBr was also determined to be very low ≤3¿10-17 cm3 molecule-1 s-1 at 300 K and ≤3¿10-16 cm3 molecule-1 s-1 at 400 K. The implications of these results to stratospheric chemistry are discussed. ¿ American Geophysical Union 1994