Total mercury (Hg) content was determined in an epiphytic moss (Dicranum montanum Hedw.); a corticolous macrolichen (Punctelia subrudecta (Nyl.) Krog) growing on tree bark; tree foliage from black cherry (Prunus serotina Ehrh.), red maple (Acer rubrum L.) and northern red oak (Quercus rubra L.); red oak leaf litter (freshly fallen leaves); the organic soil horizon; and mineral soil within an oak forest in southwestern Pennsylvania during 1999. Mean Hg concentrations of tree leaves and red oak litter were low (averaging 0.05 to 0.10 µg/g). The mineral soil contained slightly higher Hg contents (0.12 µg/g). Total Hg concentrations in the lichen species, organic soil horizon, and the epiphytic moss averaged 0.18, 0.43 and 0.50 µg/g, respectively. Based on these results, we selected the epiphytic moss and organic soil horizon for use in future studies as biomonitors to evaluate spatial and temporal variations of Hg within the mixed-hardwood forests of Pennsylvania.