Total Ozone Mapping Spectrometer (TOMS) measurements of equatorial total ozone following the eruption of Mt. Pinatubo show a decrease of up to 6% over climatology. Ozone losses begin approximately a month following the eruption, consistent with the time required for the SO2to convert to sulfuric acid aerosol. The thick aerosol layer interferes with the TOMS retrieval, but this interference is small and easily accounted for in the retrieval. Ozone values remain below climatology until December, 1991. Ozonesonde data from Natal, Brazil taken before and two months after the eruption support TOMS observations of ozone loss. These sondes show that the ozone loss region is confined to a 2–3 km thick layer between 24 and 28 k