The role of macrophytes in the biogeochemical cycle of mercury (Hg) in the Florida Everglades is poorly understood. Stable isotope tracer techniques were employed to investigate Hg uptake by sawgrass (Cladium jamaicense) from soil and atmospheric pathways and the fate of Hg after absorption. Our results suggest that soil spiked Hg-201(2+) was rapidly taken up by roots and transported to aboveground parts. The spiked Hg-201 that was transported to the aboveground parts was trapped; no release of the spiked Hg-201 from the leaf to the air was detected. Atmospheric Hg-199(0) exposure experiments revealed that the majority of the previously deposited Hg-199(0) taken into the leaf was fixed, with a very limited proportion (1.6%) available for re-emission to the atmosphere. The percentage of Hg-199(0) fixed in the leaf will help reduce the model uncertainty in estimating the Hg exchange over the air vegetation surface. We propose that sawgrass needs to be viewed as an important sink for atmospheric Hg in the regional Hg mass balance; this would have important implications for the critical loads of Hg to the Everglades. The multi-isotope tracer technique could be an effective tool to identify the role of plants in biogeochemical cycling of Hg in other ecosystems.