We used stable carbon and nitrogen isotope analyses to test the hypothesis that nectar-feeding bats Leptonycteris curasoae and Glossophaga longirostris depend on cacti and agaves as food sources in Venezuelan arid zones and to compare their trophic positions. We measured the isotopic compositions of muscle tissue in the 2 species during 1 year at 3 arid locations. Overall carbon isotopic composition (∂¹³C) of L. curasoae (−11.76‰) and G. longirostris (−13.28‰) resembled values characteristic of columnar cacti and agaves (−12.47‰), which have in common the crassulacean acid metabolism (CAM) photosynthetic pathway. L. curasoae appears to be more dependent on cacti and agaves (98% CAM in the diet) than G. longirostris (85% CAM in the diet). CAM dependence, as we designate dependence on cacti and agaves, was evidenced across sites. Level of CAM dependence slightly varied over the year only in G. longirostris. We concluded that the 2 species of bats mainly rely on CAM plants in Venezuelan arid zones. Overall nitrogen isotopic composition (∂¹⁵N) did not differ between L. curasoae (15.87‰) and G. longirostris (15.37‰). Although our results suggest that the 2 bats occupy the same trophic position, no conclusive evidence supported this observation. The strong interdependence between these bats and their host CAM plants in northern South America suggests that a disturbance affecting 1 component of the interaction would have a strong effect on the other.