Breakdown of organic matter, an important step in the ecological circulation of chemical elements, was measured in Great Smoky Mountain and Oak Ridge forests. Greatest variation in first-year weight loss of leaves in nylon net bags was due to species (Fagus grandifolia 21 percent, Acer saccharum 32 percent, Quercus shumardii 34 percent, Quercus alba 39 percent, Morus rubra 64 percent). At elevations of 5200, 3400, and 850 ft, losses for all five species averaged, respectively, 29, 34, and 40 percent for leaves placed in spruce, hemlock, and pine stands, and 35, 40, and 46 percent for leaves placed in beech, cove hardwood, and whiteoak stands.