Sometimes the most appropriate form of economic development consists of retaining native forests on steep slopes where other land uses are environmentally destructive and where economic or humanitarian considerations do not override these limitations. This is especially the case when native plant and animal species are diverse and special, as, for example, in many of the forested areas found on the humid eastern slopes of Peru's Andes Mountains. The authors recently evaluated the biological diversity there. They provide a brief outline of their findings and conclusions.