Sulfate reduction rates in Sapelo IslandSpartinamarsh soils were assessed by a radiometric method. There was a significant linear correlation (r= 0.93) between the H235S produced and incubation period, and the regression line passed close to the origin. Sulfide reduction rates for the topmost 35 cm of soil in the short and tallSpartinazones were 62.3 and 201 mmol sulfide/m2/lb day, respectively. To reduce sulfate at these daily rates, the sulfate‐reducing bacteria would require a maximum of 67 and 36% of the organic carbon produced by the summer crops of short and tallSpartina,respectively. In both zones, highest rates occurred in the 0‐ to 5‐cm layer. In the shortSpartinazone, 80% of the sulfate reduction in the topmost 35 cm occurred in the 0‐ to 5‐cm layer, whereas a value of 29% was found for the same situation in the tallSpartinazone. In the topmost 10 cm of the shortSpartinazone, some sulfate appeared to be immobilized as organic sulfate.