Absorption features of the v1 band of SO2 have been identified in high resolution infrared solar absorption spectra recorded from Mauna Loa, Hawaii, on July 9 and 12, 1991, shortly after the arrival of the first eruption plume from the Mt. Pinatubo volcano in the Philippines. A total SO2 vertical column amount of (5.1¿0.5)¿1016 molecules cm-2 on July 9 has been retrieved based on nonlinear least-squares spectral fittings of 9 selected SO2 absorption features with an updated set of SO2 spectral parameters. A SO2 total column upper limit of 0.9¿1016 molecules cm-2 deduced from measurements on September 20--24, 1991, is consistent with the dispersion of the SO2 cloud and the rapid conversion of the SO2 vapor into volcanic aerosol particles. ¿American Geophysical Union 1992