A method for formulation of synthetic substrata (soils and sediments) is given. Submersed, wetland, and terrestrial plants, earthworms, crustaceans, and vertebrates were maintained on synthetic substrata composed of various amounts of commercially available sand, clay, silt, and particulate and dissolved organic matter. Organic contents of the synthetic substrata were 3, 5, 7.5, and 10% by weight. All test species survived and grew well in the substrata. It is suggested that synthetic substrata have some advantages over natural substrata in tests with plants and animals. Among the advantages are: synthetic sediments may be formulated for specific studies, differences in texture and chemical characteristics between batches are minimized, and the substrata are not contaminated by anthropogenic substances as are many natural soils and sediments.