Environmental mercury exposure of birds through atmospheric deposition and watershed point-source contamination is an issue of increasing concern globally. The saltmarsh sparrow (Ammodramus caudacutus) is of high conservation concern throughout its range and the potential threat of mercury exposure adds to other anthropogenic stressors, including sea level rise. To assess methylmercury exposure we sampled blood of the northern nominal subspecies of saltmarsh sparrows (A. c. caudacutus) nesting in 21 tidal marshes throughout most of the species' breeding range. Blood of tree swallows (Tachycineta bicolor) was sampled concurrently at three of these sites to provide a comparison with a well-studied songbird that is a model species in ecotoxicology. Arithmetic means (±1 SD) ranged from 0.24 ± 0.06 μg g(-1) wet weight (ww) in Connecticut to 1.80 ± 0.14 μg g(-1) ww in Massachusetts, differing significantly among sites. Comparison to tree swallows indicates that mercury exposure is significantly higher in saltmarsh sparrows, making them a more appropriate bioindicator for assessing risk to methylmercury toxicity in tidal marsh ecosystems.