Feeding habits of the endangered Ozark big-eared bat (Corynorhinus townsendii ingens) in eastern Oklahoma, USA, were studied from July 1987 through July 1988. Diets were determined from microscopic analysis of fecal pellets and compared with arthropods collected in Malaise traps. Although lepidopterans comprised only 21.5% of the available prey, they occurred in > 90% of the pellets examined and accounted for > 85% of the volume of prey consumed. Dipterans, coleopterans, and homopterans occurred in 18.3%, 10.6%, and 6.7% of the feces, respectively, but each accounted for < 5% of the volume of prey consumed. Trichopterans, hymenopterans, and neuropterans also were found in feces but in trace amounts. Our results support the classification of C. t. ingens as a moth specialist, but additional insights are needed to fully understand how its feeding tactics conform to the allotonic frequency hypothesis (i.e., avoiding detection by eared moths). Conservation of this highly endangered North American bat will require, in part, maintenance of habitats capable of supporting abundant populations of Lepidoptera.