The Airborne Southern Hemisphere Ozone Experiment (ASHOE) is designed to examine the causes of ozone loss in the Southern Hemisphere lower stratosphere and to investigate how the loss is related to polar, mid-latitude, and tropical processes. ASHOE will be conducted in concert with the campaign, Measurements for Assessing the Effects of Stratospheric Aircraft (MAESA), whose focus is to provide information about stratospheric photochemistry and transport forassessing the potential environmental effects of stratospheric aircraft. These combined objectives will be met by a series of flights of the National Aeronautics and Space Administration (NASA) ER-2 high-altitude research aircraft from Christchurch, New Zealand, and on transit flights from Moffett Field, California, to Christchurch via Hawaii and Fiji. Flights of the remotely piloted vehicle Perseus, or possibly balloons, to higher altitudes in the tropics and mid-latitudes will also be made. There are several compelling reasons to study processes relating to ozone depletion in the Southern Hemisphere and tropical lower stratosphere.