We present the first simultaneous measurements of HOx, NOx, and Clx radicals in the middle stratosphere obtained during a balloon flight at 34 ¿N in September 1989, along with calculations from a photochemical model, to show that NOx catalytic cycles dominate loss of ozone (O3) for altitudes between 24 and 38 km; the observed abundance of ClO is lower than that expected for altitudes above 30 km on the basis of models using recommended rates and cross sections, reducing the relative importance of the Clx catalytic cycles for loss of O3; and removal rates of O3 derived from observed concentrations of rate limiting HOx, and NOx, and Clx radicals balance computed production rates for altitudes between 32 and 38 km, a region where ozone is expected to be regulated primarily by photochemical processes. ¿ American Geophysical Union 1996