Recent aircraft and balloon borne measurements of OH and HO_2 are reviewed. The authors demonstrate the ability of the laser-induced fluorescence technique to provide accurate, high signal to noise ratio measurements of OH throughout the upper troposphere and stratosphere. HO_2 is measured as OH after gas phase chemical titration with nitric oxide. The addition of the HO_x measurement capability to the suite of instruments aboard the NASA ER-2 aircraft has provided a wealth of new information about the processes that determine the concentration of ozone in the lower stratosphere. These simultaneous, in situ measurements provide a unique test of our understanding of the mechanisms that control the odd-hydrogen chemistry of the lower atmosphere.