La Selva Biological Station, a lowland tropical rain forest site in Costa Rica, is currently one of the world's most active centers for research in tropical biology. The existence of a modern biological laboratory adjacent to 50,000 ha of protected forests spanning a 3000-m altitudinal transect is unique in the humid tropics. The recent addition to La Selva of 600 ha of altered and/or manipulable habitats has fostered a quantum increase in large-scale process-oriented research. An exceptionally diverse spectrum of researchers and academic institutions are taking advantage of these opportunities. A critical multidisciplinary mass has been reached at La Selva, which is simultaneously stimulating new lines of research and pushing existing laboratory facilities to their limits. With this Biological Facilities Center proposal, funds are requested to equip a modern analytical laboratory to serve this growing network of interrelated research efforts. This analytical laboratory with first-rate instrumentation (GIS and standard and state-of-the-art equipment to permit onsite evaluation) will greatly intensify the application of new techniques to the biological study of tropical rain forest. Owing to La Selva's ties to a large proportion of the U.S. academic community, this facility will benefit users from an unusually broad geographic and disciplinary spectrum. The development of technologically advanced infrastructure at a rain forest site with an exceptional record of multidisciplinary research will have a major impact on the next generation of knowledge of tropical ecosystems.