AbStrdCt. Elevational patterns of species richness and endemism in birds, mammals, reptiles, amphibians, and butterflies, in two mountain ranges in southern Mexico are analysed. In all five taxonomic groups and both mountain ranges, although species richness is concentrated in the lowlands, endemism is concentrated at interme? diate and high elevations. If conservation efforts are to focus on the preservation of biotic elements unique to Mexico, efforts should be focused on highland habitats instead of on the highly diverse lowlands.