We determined the foraging range of Mexican free-tailed bats (Tadarida brasiliensis mexicana) that spend summer in Carlsbad Cavern, Carlsbad Caverns National Park, New Mexico. We captured bats at varying distances and directions from the cavern and attached a radiotransmitter to each. During daylight hours, we entered Carlsbad Cavern to determine if bats with radiotransmitters were present in the maternity roost. The distribution of localities where captured bats returned to Carlsbad Cavern indicated a nightly foraging range of at least 56 km from Carlsbad Cavern. Our data indicated that the colony eventually dispersed in every direction after leaving the cavern each evening and foraged in a space nearly 4,000 km³. This study was the first to document use of water sources on property of Carlsbad Caverns and Guadalupe Mountains national parks, the Lincoln National Forest, and other sites in southeastern New Mexico and western Texas by members of the colony of T. b. mexicana that reside in Carlsbad Cavern.