The kinetics of the title reaction have been investigated at 298 K using time-resolved long-pathlength absorption spectroscopy to monitor the temporal behavior of IO following 351-nm laser flash photolysis of NO2/I2/CH3SCH3(DMS)/N2/O2 mixtures. We obtain an upper limit bimolecular rate constant for the IO+DMS reaction of 3.5¿10-14 cm3 molecule-1 s-1; this upper limit is nearly 3 orders of magnitude slower than two previously reported measurements. Our results suggest that coupling of the marine sulfur and iodine cycles via the IO+DMS reaction is negligible. ¿ American Geophysical Union 1990