A balloon-borne photoelectric counter and jet impactor have been used to examine the southern hemisphere stratospheric aerosol from late 1974 to mid-1976. Changes in particle morphology and loading observed in this period are consistent with a new source of aerosol in 1974. In the 10- to 16-km altitude range the loading of particles with r>0.15μm increased by slightly greater than a factor of 2 from September 1974 to July 1976, while the loading of particles with 0.028μm0.15μm in the 1975 southern winter was only about one-fifth observed at northern mid-latitudes in the preceding northern winter.