More than 60 hours of airborne cloud condensation nuclei (CCN) measurements made during the First Aerosol Characterization Experiment (ACE#1) south of Australia are presented and analyzed. These ambient measurements covered more than half of the aircraft time on station between 7 km and 30 m altitude during the late spring/early summer season over the Southern Ocean. The complete CCN spectra from 1.2 to 0.02% and condensation nuclei (CN), particles greater than 0.01 μm, concentrations are presented. The CN and CCN concentrations at 1.2 and 0.2% supersaturation compared well with long-term surface measurements at Cape Grim, Tasmania. Lower concentrations, especially for CN, were associated with cloudier regions. Higher concentrations, especially for CN, were found in air masses that were or had recently been closer to land. Nonetheless, these data should be representative of clean maritime conditions. ¿ 1998 American Geophysical Union