The role of macrophytes in mercury (Hg) cycling in the Florida Everglades ecosystem has not been fully understood. In this study, a stable isotope ((199)Hg(2+)) addition technique was used to trace the methylation, uptake, and translocation of Hg by sawgrass ( Cladium jamaicense ) and quantitatively evaluate the contribution of atmospheric and soil Hg to Hg in sawgrass leaves and below-ground biomass. The results showed that spiked (199)Hg(2+) could be rapidly methylated to monomethylmercury (Me(199)Hg) in the soil of the sawgrass pots. Only small portions of total Hg (THg) and monomethylmercury (MeHg) in the soil could be taken up by sawgrass, indicated by the ratios of T(199)Hg and Me(199)Hg (tracer) concentrations in the sawgrass below-ground biomass (BGBM) over that in the soil (6.50 ± 1.9% and 12.8 ± 3.6% for THg and MeHg, respectively). Concentrations of T(199)Hg (tracer) and Me(199)Hg (tracer) in sawgrass leaves only accounted for 5.50 ± 2.8% and 15.6 ± 4.0%, respectively, of that in the BGBM, implying that the fractions of mercury species transported upward by sawgrass were also small. Statistical analysis (t test) showed that sawgrass preferred MeHg over THg in both uptake and upward translocation. The majority (>90%) of THg in sawgrass leaves were estimated to be obtained from atmospheric Hg, rather than from soil, suggesting that assimilation of atmospheric Hg could increase the overall Hg stock in the Florida Everglades ecosystem. The finding about foliar uptake of Hg is especially important for a better understanding of mercury cycling in the Everglades, given the large amount of sawgrass biomass in this ecosystem.