West Chester University, in cooperation with the Amazon Center for Environmental Education and Research, has developed a Phytohabitat Index model for eth-nophamacologically important plants found in the tropical rain forests of the Peruvian Amazon. The Index identifies the most probable locations in the rain forest for these plants. To calculate the Index, a series of numerical weights and ratings are given to the following factors that are important to the spatial distribution of plants: forest types, soils, geology, ecological life zones, physiography, and phases of forest succession. A geographic information system (GIS) was used to process data and calculate the index from digital maps, data from low level aerial photographs, and Landsat TM satellite images. Field data were then collected to verify the predictive accuracy and precision of the index. In each case, the index accurately predicted the occurrence of the most probable habitats for all of the plants in this study. The study was conducted in a 4700 square mile area of northeastern Peru near the city of Iqui-tos, a region with some of the highest plant biodiversity on the planet. The project was aided by the expertise of local ethnobotanists and shamans practicing natural healing in the region using these plants.