Used carbon stable-isotope techniques to test the hypothesis that the pallid bat (Chiroptera: Vespertilionidae) obtains substantial amounts of carbon from plants of the Cactaceae and Agavaceae, which employ the crassulacean acid metabolism (CAM) photosynthetic pathway, in areas where there are bat-adapted flowers of cacti and agaves. Analysis revealed significant geographic variation in carbon composition of the pallid bat during the blooming periods of bat-visited cacti and agaves. Although the pallid bat probably visits flowers to eat insects, it is a legitimate pollinator of bat-adapted CAM plants and may represent an early stage in the evolution of nectarivory and frugivory in the Vespertilionidae. -Authors