Results of recent International Ultraviolet Explorer (IUE) observations of Venus made on January 20, 1987, and April 2 and 3, 1988 along with a reanalysis of the 1979 observations (Conway et al., 1979) are presented. The observations indicate that the amount of sulfur dioxide at the cloud tops of Venus declinced by a factor of 8¿4 from 380¿70 ppb in 1979 to 50¿20 ppb in 1987 and 1988. These values are consistent with the Pioneer Venus results (L. W. Esposito. A recalibration of the solar flux for Pioneer Venus results and a comparison of existing SO2 measurements on Venus, unpublished manuscript, 1989). We identify absorption features of sulfur monoxide for the first time, and estimate the SO mixing ratio above the cloud level is 20¿10 ppb for 1979. This is consistent with photochemical models by Winick and Stewart (1980) and Yung and DeMore (1982) and with the upper limit from Wislon et al. (1981). ¿ American Geophysical Union 1990