The Galileo Near Infrared Mapping Spectrometer was used to investigate the distribution and properties of sulfur dioxide over the surface of Io, and qualitative results for the anti-Jove hemisphere are presented here. SO2, existing as a frost, is found almost everywhere, but with spatially variable concentration. The exceptions are volcanic hot spots, where high surface temperatures promote rapid vaporization and can produce SO2-free areas. The pervasive frost, if fully covering the cold surface, has characteristic grain sizes of 30 to 100 &mgr;m, or greater. Regions of greater sulfur dioxide concentrations are found. The equatorial Colchis Regio area exhibits extensive snowfields with large particles (250 to 500 &mgr;m diameter, or greater) beneath smaller particles. A weak feature at 3.15 &mgr;m is observed and is perhaps due to hydroxides, hydrates, or water. A broad absorption in the 1 &mgr;m region, which could be caused by iron-containing minerals, shows a concentration in Io's southern polar region, with an absence in the Pele plume deposition ring.¿ 1997 American Geophysical Union